bas van der werk, thomas gerrits & george koolman

Design of a Bi-Directional Fly-back DC/DC ConverterFor a stand-alone solar-powered eBike charging station

Bas van der Werk, Thomas Gerrits & GeorgeKoolman

Bach

elorT

hesis

Design of a Bi-Directional FlybackDC/DC Converter

For a stand-alone solar-powered eBike charging station

Bachelor Thesis

Group B2George Koolman 4270975Bas van der Werk 4346785Thomas Gerrits 4355075

June, 2017

Faculty of Electrical Engineering, Mathematic and Computer Science (EEMCS)Delft University of Technology

Acknowledgements

We would first like to thank our supervisor dr. ir. P. J. van Duijsen for giving us an interestingand technically challenging BAP free elective and also for taking the time from his busy scheduleto intensely help us understand the power concepts and challenges faced in DC/DC converters.It was surely helpful and motivated some of us to consider further pursuing a masters degree inpower engineering.

Secondly, we would like to thank Joris Koeners, Harrie Olsthoorn, Chris Swanink, Bart Roden-burg and the Dream-hall for helping us get the needed equipment and location to successfullywork on our BAP thesis.

Lastly, we would also like to thank Pavel Purgat for his expertise and advice during trou-bleshooting of our prototype and Martin Schumacher for being the administrative contact.

Design of a Bi-Directional Flyback DC/DC Converter

Executive Summary

This document is the bachelor graduation thesis of BAP Group B2. Together with BAP GroupB1 the objective of this project was to create a control network and DC/DC converter implemen-tation capable of fast, analog power management with active, remote-control and -interfacing ofmultiple converter’s energy flows. The system will be designed to function in the solar-poweredeBike charging station on the TU Delft campus.

This document specifically is concerned with the design, simulation and testing of the DC/DCconverter. The thesis presents a bi-directional flyback DC/DC converter design and prototypewith analog power management, universal control signals and high integration potential.

These aspects are accomplished by building upon the traditional flyback DC/DC converter de-sign with respect to circuit topology, power-flow control, connectivity and accessibility. Thedifficult regulation and measurement of DC power flow has been reduced to a set of analogsignals interpretable by any microcontroller, easing the integration of the converter into largerenergy and control networks.

A working prototype is presented and the inner-workings of the electrical circuit are discussedand evaluated in detail. The converter is tested beyond the limit of the design requirements andthe performance is documented. Provided are possible reasons for malfunctioning and guide-lines for future improvements.


Table of Contents

Executive Summary ii

1 Problem Description 11.1 Problem Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Technical Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Design Description 32.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2.1 Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.2.2 Switching Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.2.3 Integrated Circuit PWM controller . . . . . . . . . . . . . . . . . . . . . . . 14

2.3 Topology Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.4 Subsystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.4.1 Peak Current Mode Controller . . . . . . . . . . . . . . . . . . . . . . . . . 172.4.2 Measurement Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192.4.3 Digital to Analog Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.4.4 Direction Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.4.5 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2.5 Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Simulations 24

3.1 Uni-directional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.2 Bi-directional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4 PCB Design 294.1 Design Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5 Evaluation 315.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.2 Prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325.3 Testing and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335.4 Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.5 Next steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

A Appendix 43


Problem Description

1.1 Problem Scope

The current electrical power grids have seen a considerable increase in contributors and recipientsin the form of off-shore wind-farms, enormous solar-fields, electric vehicle (EV) infrastructureand extensive consumer electronics, among others. The growth of these non-conventional powerelements in the distribution chain conflict with the functionality of traditional electrical grids,designed in the 20th century. The traditional grids struggle with the energy surges and droughtsproduced by sustainable energy technologies such as solar and wind, and do not make use ofthe technologies available in the 21st century.

In new, state-of-the-art grids not only power, but also information is generated and exchangedin the infrastructure. This allows analysis of the power flow, and control and scheduling of theenclosed system. Energy demands can be adjusted to meet the available supplies, whereas inthe current systems, demand control is severely lacking.

The purpose of this thesis is to design a robust bi-directional flyback DC/DC converter withfast, analog control and the potential of integration into a vast range of prospective electricalgrids. In it’s most simple form the converter needs to be able to charge Lithium-Ion batteriesof electric bicycles and it will be designed as a key element of the solar-powered eBike chargingstation developed at the TU Delft faculty, EEMCS[19].

1.2 Technical Review

Energy flow Managing and controlling the flow of energy is an important aspect in currentelectrical grids. Small or large grids would benefit from integrated power management on ananalog level. New DC-microgrids, like solar-powered green villages[2] or DC-fed automotiveboardnets, are being designed to function completely free from any external energy source.These grids have a significant amount of varying supplies, loads and hybrid elements like bat-teries. They need to manage their energy flow and storage with complex algorithms in order tofunction efficiently and reliably.

Switch mode power supplies One possible way to do this is with the use of a flyback con-verter. The flyback converter that is proposed is a subcategory of the so called Switch ModePower Supplies (SMPS). In its most basic form a switch mode power supply uses a switchingcomponent, an inductor and a rectifying diode to transfer DC or AC power to DC loads, whileconverting the electrical characteristics of the power flow. or transfer energy from the inputto the output. Currently, SMPS are rapidly replacing linear regulated power supplies in most


1.3 Design Requirements 2

modern electronic devices. They often show higher efficiency, better output voltage regulationand compacter size.

Linear power supplies basically consists of a dissipative series regulator and a transformer.Normally the transformer is a heavy 50/60 Hz transformer which increases the cost, size andweight. Efficiencies of a linear voltage regulator are quite low, often not higher then 60 percent.SMPS however, are able to function at frequencies that range from several hz to several hundredkHz. Especially when looking at frequencies of a few tens of kHz the SMPS shows great results,and efficiencies up 80 or 90 percent can be achieved. Switching at higher frequencies also reducesthe size of filtering components and the transformer[3].

1.3 Design Requirements

The converter will be used in the solar-powered eBike charging station which determines a setof initial design guidelines. A couple of general design requirements(req) and wishes(wish) havebeen formulated to fulfill this intention, while also keeping the door open for future innovationand integration.

• The output power needs to be 110 Watts (req).

• The input voltage can vary between 36 and 48 volts (req).

• Add functionality at low input voltages ranging from 12V and up (wish).

• The required output power needs to be met at an output voltage of 48V (req).

• The flyback converter has a wide output voltage range that can vary between 12V and48V (wish).

• The flyback converter needs to have fast, analog cycle-to-cycle current limiting (req).

• The switching frequency needs to be settable to a maximum of 125 kHz (wish).

• The flyback converter needs to operate in discontinuous current mode (wish).

• The flyback converter needs to be able of bi-directional energy conversion (wish).

• Low ripple on the output voltage line (wish).

• The flyback converter needs to be controlled by a simple microcontroller, while providingmeasurements of the DC power flow (req).

• The flyback converter needs to be applicable in a number of other circumstances, such assmart DC-grids (wish).

• The flyback converter needs to be a robust design to maximize lifetime (wish).


Design Description

2.1 Overview

The bi-directional flyback converter proposed is part of a larger network of multiple DC/DCpower converters and control circuitry shown in figure 2-1. This system is able to effectivelymanage, control and display the energy flow wherever the power converters are implemented.The conversion of the DC power happens on-board by the use of the flyback SMPS circuittopology, controlled by digital commands received from a slave. The master and slave receiverelevant information about the power flow from the converter and determine a course of action.All this information is sent to a server where real-time status can be observed and commandscan be sent back to the converter from any device connected to the internet.

Figure 2-1: Simplified diagram of the complete standalone charging system

Our design focuses explicitly on the power converter block and the implementation of the controlsignals and measurements to and from the slave. The power converters in this block are all bi-directional flyback converters.

These converters are designed keeping all requirements of section 1.3 in mind, while also tryingto fulfill as much of the additional wishes as possible.


2.1 Overview 4

Flyback Topology

The flyback topology is derived from the buck-boost topology. This is achieved by replacing theinductor in a buck-boost converter with a coupled inductor, such as gapped core transformers[21]. The characteristics of the transformer enables the use of less components, while stillretaining the same functionalities. Making the flyback a simpler and cheaper option.

In its simplest form the flyback consist of a switch on the primary side of the transformer anda diode with output capacitor on the secondary side. Bi-directionality is achieved by mirroringthe components on both sides as shown in figure 2-2.

Figure 2-2: Simplified schematic of a bi-directional flyback converter

For the sake of simplicity the flyback topology will be explained with a one directional flyback.The energy transfer is described in two states, the ON and OFF state.

ON state In this state the MOSFET Q1 is turned on, meaning it will conduct and Q2 is turnedoff. The energy from the input is stored inside the transformer as magnetizing inductance. Theoutput diode (internal MOSFET body diode Q2) is off (reverse biased) and energy is suppliedto the load from the output capacitors [12].

OFF state Here MOSFET Q2 is turned off, the energy inside the primary side transfers tothe secondary inductor, the voltage across the secondary inductor reverses and the internalMOSFET body diode Q2 turns on (forward bias). The stored energy is then supplied to theoutput capacitor and load [12].

Figure 2-3: Currents during DCM operation

The flyback converter can operate in twomodes, discontinuous current mode (DCM)and continuous current mode (CCM). InDCM the current in the secondary inductoris fully delivered to the load before the nextswitching cycle. For our transformer design,this requires the duty cycle (D) to be under50% (see figure 2-3 and section 2.2.1). InCCM on the other hand the next switchingcycle begins while the secondary inductor stillhas current running through it [12]. For ourapplication DCM is wishful.


2.1 Overview 5

The advantages of DCM are:

• Higher efficiency.

• Faster transient response.

• Low primary inductance, thus making the transformer smaller [22].

However there are some drawbacks. DCM produces parasitics that cause higher peak currentswhich results in higher peak voltages over the MOSFET that can cause failures[21]. For thisreason extra switching circuitry has been added to promote robustness of our flyback converter.

Converter Power management

Controlling the energy flow, there are PWM (Pulse Width Modulation) control IC’s on eitherside, driving the MOSFETs. These produce the appropriate duty cycle to match the voltage setpoint (Vsetp), current limit (Ilim) and energy directon (DIR), received from the microcontroller.

Figure 2-4: Control and measurement connections to the converter

Furthermore, the PWM controller itself is controlled via multiple subsystems. These subsystemsconsist of a Measurement Bridge, Digital to Analog Converters (DAC) and a Direction Com-parator, and function as the translational step between the converter and the microcontroller.The measurement bridge does four measurements, the current and voltage of both the primaryand the secondary side. These measurement signals are sent to the microcontroller. Using thesemeasurements the microcontroller determines a course of action depending on implemented al-gorithms. The microcontroller initially sends two PWM signals back to the converter, Vsetpand ILim. These digital signals are received by the DAC and converted to an analog signal.The Vsetp signal ’sets’ the output voltage and ILim limits the suppliable current. A third signalis sent from the microcontroller to determine the direction of energy flow through the flyback.Either from left to right or from right to left (see Figures 2-4 and 2-5).

Figure 2-5: PCB signal conversion subsystems


2.2 Components 6

2.2 Components

To obtain a properly functioning flyback converter it is essential to obtain components that workaccurately and effectively. Especially the choices regarding the switching component, PWMcontroller and the transformer are crucial. For each of these component design parameters needto be established. This section gives an overview of the considerations made concerning thesethree components.

2.2.1 Transformer

In flyback converters, the transformer is a crucial component that needs to be carefully designed.The transformer needs to combine the functions of power transfer, energy storage, and galvanicisolation[12]. Many facets come into play when designing the coupled inductor. For macro-circuit design and operation, the turn ratio

(Np

Ns

)and magnetic core saturation (Bsat) are the

most important factors. These aspects determine the input and output voltage and currentcharacteristics of the overall circuit, as well as frequency limitations and ripple current[8].A variety of other parameters are inherent to coupled inductors that influence the efficiency,stability and complexity. These include, but are not limited to; the primary and secondarycoil inductance and turns, the parasitic inductance, the resistive winding and magnetic corelosses, the core shape and air-gap. These parameters are a subject of initial design and haveconsiderable importance, as they are a key factor in the overall performance and lifetime of theconverter. This section gives insight in the design of a transformer[11].

Requirements

Besides the general requirements stated in section 1.3 there are a couple of requirements andwishes established specifically for the transformer.

• The transformer winding ratio is 1:1 in order to keep the currents on both primary andsecondary side the same (wish).

• Leakage inductance needs to be as low as possible in order to prevent high over-voltagespikes, ringing and losses (wish).

• The maximal flux density is set to 300 mT. The flux density determines how much en-ergy can be moved through a transformer. High flux density means more power can bemoved through the transformer, however when the value is too high, power losses will risedrastically. 300 mT is often used as a rule of thumb[5] (req).

• The inductance value needs to be chosen as big as possible in order to minimize peakcurrents (wish).

• The core needs to be chosen as small as possible in order to have as few losses as possible(wish).

• The calculated number of turns necessary needs to fit on the coil former (req).

• The air gap should be as wide as possible in order to increase the inductance factor thusminimizing the number of layers and core size needed (wish).


2.2 Components 7

Design

The design process of a transformer can be subdivided into several steps. The first step thatneeds to be made is picking a core type and size. Important requirements that need to be takeninto account when looking at the core size are the flux density and the maximum output power.These will give a rough estimation on the type and size, however this does not mean that theoriginally chosen core is the correct one, since there is a possibility that a requirement will notbe met and a different core needs to be chosen.There is a wide variety of cores ranging from the magnetically superior POT cores to the morecheaper E and EE cores[9]. Since the E and EE cores offer the lowest cost with respect to othercore types the focus will initially be on these type of cores.The size of the core is based on an estimation of the amount of turns and output power. Fur-thermore, it is better to pick a bigger gap before picking a bigger core size. A smaller core hasless heat radiation, lower losses and lower parasitic capacitances[10].

Next step is to calculate the number of turns. The following formula applies for the fluxdensity,

B = AL · n · Ip,peakAcore

(2-1)

with,

• n, the number of turns.

• Ip,peak(A), the peak current at the primary side of the transformer.

• AL(H), the inductance factor.

• B(T), the flux density.

• Acore(m2), the core area.

Rewriting this to the number of turns results in,

n = B ·AcoreAL · Ip,peak

(2-2)

The peak current of formula 2-2 is still unknown, which means that other parameters need tobe looked into first before making an assumption on the number of turns.For the output power the following formula applies,

Pout = 0.5 · Lp · I2p,peak · f (2-3)

with:

• Pout(W), the output power.

• Lp(H), the primary inductance.

• f(Hz), the frequency.

Keeping in mind the required output power of 110 W, the peak current can be determined.Rewriting formula 2-3 to the peak current results in,

Ip,peak =√

2 · PoutLp · f

(2-4)


2.2 Components 8

This results in another unknown parameter, the primary inductance. The primary inductanceis related to the peak current via the following equation,

Ip,peak ≤VB ·D · T

Lp(2-5)

with,

• D, the duty cycle.

• T(s), the period.

• VB(V), the input voltage.

Rewriting this to an expression for the primary inductance results in,

Lp ≤VB ·D · TIp, peak

(2-6)

Substituting equation 2-6 into equation 2-4 results in,

Ip,peak ≤2 · PoutVB ·D

(2-7)

Taking into account that the input voltage can vary between 12V and 48V and the duty cycleis less then 50 percent, the peak current and number of turns can be calculated.The number of turns is related to the inductance via the following formula,

Lp = n2 ·AL (2-8)

with,

• AL(H), the inductance factor

The inductance factor is the inductance of the coil when n is equal to 1 and can be found inthe datasheet of the core type[7]. Since one of the established requirements is a turns ratio of1:1, the primary inductance will be equal to the secondary inductance(Lp = Ls = L). The peakcurrent and the inductance value are important parameters to consider when looking at theduty cycle, since the current rises with a factor di

dt = V/L. If it is not able to reach the necessarypeak current within it’s duty cycle, the desired output power cannot be achieved. Which meansthat the peak current needs to be raised and/or the inductance needs to be reduced[10]. Takingthis data into account a core size is picked with a certain gap length. The number of turns canbe calculated and the peak current can be measured. These values are used to check whetherthe flux density is below 300 mT. When the flux density is above 300 mT, a bigger gap is chosen.When this isn’t enough, a bigger core is used. When the flux density has the correct value onehas to check if the number of turns needed to gain the specified value of the flux density fitson the core, which could have an effect on the inductance value. Lastly the inductance value iscalculated using equation 2-8.

After the steps described above have been done, the winding method needs to be determinedand the DC resistance needs to be estimated. The second of which is done using the followingequation,

R = ρ · lA

(2-9)

with,


2.2 Components 9

• R(Ω), the DC resistance of the wire.

• l(m) = 2π · r · n, the length of the wire.

• A(m2) = π · r2, the surface of the wire.

• ρ(Ω ·m), the resistivity of the material.

Rewriting equation 2-9 gives,R = ρ · 2 · π · rcore · n

π · r2wire

(2-10)

with,

• rcore, the radius of the middle shaft of the core

• rwire, the radius of the wire

With respect to the winding method it is important to decide how many layers are needed.When it is necessary to have multiple layers it is possible to make use of interleaving[5]. In-terleaving is a winding method at which the secondary winding is ’interleaved’ in between theprimary winding. For instance when using four layers, two primary and two secondary, theorder of layers would be P-S-S-P. The benefit of this method is that there will be no magneticfield at the boundaries of the different sections.Based on the given formulas stated above the transformer parameters can be determined.

Component selection As already mentioned the choice has been made to use the E coretype. Preferably a core with low leakage and wide windows. A viable option that meets thesespecifications would be the ETD core. The size can be relatively small for the application itwill be designed for. The first core that will be looked at is the ETD29. Basically the smallestETD core type there is on the market right now. The air gap is taken as big as possible, whichin this case is 1 mm. This gives an inductance factor of 124 ·10−9 (H/turn) and a core area of71 ·10−6(m2)Now that the core type and size is determined the other parameters need to be established inorder to check whether the transformer meets the requirements. First of all equation 2-7 is usedto determine the peak current before the inductance value is calculated. This value is maximalat a low input voltage of 36V and at an output power of 110 Watt resulting in a peak currentof 12.2 Ampere. Using this value the number of turns can be determined using equation 2-1resulting in n equal to 14 turns. Using equation 2-8 the inductance is determined at 24 uH.Lastly, the core needs to be winded. Initially the selected material for winding is copper,which has a resistivity of 1.68 ·10−8 (Ω·m). Using equation 2-9, a rough estimation of the DCresistance can be made. Using n equal to 14 results in a DC resistance of 5.5 mΩ over theprimary and secondary side. In order to fit the number of turns on the core a wire thickness ispicked of 1.25mm. The available space for the winding is equal to 22, dividing 22 by 1.25 equalsapproximately 17 turns. The transformer consist of one primary layer and one secondary layer.Both winded in the same direction in order to meet the polarity of the transformer.After the transformer has been winded, the transformer should be connected to the spectrumanalyzer. This device determines the inductance value, the leakage inductance and the ACresistance. Section 5.3 describes the results.


2.2 Components 10

Remarks

Skin effect and with it the skin depth are also factors that can be of importance for the trans-former. Skin effect is the tendency of AC currents to distribute itself in such a way that the cur-rent density at the surface is higher than at the center, see figure 2-6.

Figure 2-6: Skin effect in a round wire

The parameter δ, called the skin depth, de-termines how close the current flows along thesurface of the conductor[20]. Ideally, all thewindings should have a single layer. Whenusing a single layer for both the primaryand secondary layer, the layers can be muchthicker than the skin depth without adverseeffects[18]. The proximity effect should alsobe mentioned. The proximity effect occurswhen an AC current in a conductor causeseddy currents in close by conductors[13].Both factors need to be taken into accountwhen testing the transformer with the se-lected wires. For instance, when the AC resistance of the transformer is unexpectedly highperhaps other winding material needs to be used to counteract this.For the determination of the AC resistance the formula of Dowel can be used. This formulais used since it takes into account, among other elements, the skin effect and the proximityeffect[27].


2.2 Components 11

2.2.2 Switching Component

The switching component of a flyback converter is one of the most vulnerable parts within aflyback. For maximum system robustness and reliability a properly rated power MOSFET hasto be selected along with a high efficiency. The MOS family has two main branches, the PMOSand the NMOS. The basic functionality is the same, but the operation modes and applicationsdiffer between the two. In most cases the NMOS is a better choice due to the orientation ofits internal body diode, and better circuit performance and efficiency compared to the PMOS,therefore this type of MOSFET will be used[6]. Things to consider with the selection are;blocking voltage, on-state current, switching frequency, switching losses, internal body diodeand more.

Requirements

Besides the requirements stated in 2.3, the specific requirements for the the switching MOSFETsare:

• Breakdown voltage (VDSS) of the MOSFET has to be able to withstand the high voltagesencountered during the switch in OFF state (req).

• The maximum drain to source current (ID) of the MOSFET needs to be rated for themaximum current flowing during the ON state (req).

• The MOSFET has to be robust, meaning being avalanche rated and should be accompa-nied by fail safe circuits (wish).

• Low power losses within the MOSFET (wish).

• The MOSFET has to be able to switch at 125 KHz (wish).

• Gate-to-source voltage VGS has to be compatible with the PWM controller (req).

Component selection

First step in determining the right switching component or NMOS to choose for a flybackrealization is to take a look at the ON and OFF states of our switch. In the ON state, the voltageacross the MOSFET drops to nearly zero, current flows linearly into the primary inductor ofthe transformer and energy gets stored into the transformer. Here the rating to take intoconsideration is the maximum drain to source current ID. This would have to be larger thanthe maximum current flowing in the primary side of the transformer which is for our transformer12.2A, mentioned in 2.2.1. When the MOSFET turns off, an extremely high voltage is generatedacross the device as shown in figure 2-7. It is because of this that the break-down voltage VDSS isa crucial parameter to consider in flyback power supply design[24]. This high voltage generatedconsists of the (maximum) output voltage across the secondary reflected back through thetransformer and multiplied by the turns ratio (nV o), (maximum) input voltage (VinMAX) anda spike voltage due to the effects of parasitics caused by the primary leakage inductance (Llk1)and MOSFET output capacitor (Coss) labeled as VLleak (detailed explaination of this resonanceis found in [21]). All these voltages are in series with each other making the calculation forminimum VDSS :

VDSSmin = nV oMAX + VinMAX + VLleak (2-11)


2.2 Components 12

For our flyback nV oMAX +VinMAX is around 96V to leave some room for the leakage inductionspike a double of the minimum VDSS is recommended. Thus, a VDSS in the range of 150V-200Vshould be sufficient.

Figure 2-7: Resonance caused during DCM operation [21]

Second step in selecting a MOSFET is to take generated power losses into consideration. Thepower loss in a MOSFETmostly comes from two sources, the conduction losses and the switchinglosses. Conduction losses are caused by the resistive element in the MOSFET RDS(on). Thiselement dissipates power as the current is conducted through the MOSFET and is inverselyproportional to the size of the device [23]. Also a high VDSS has some influence as theseMOSFETs tend to have higher conduction losses [24]. Switching losses, on the other hand, arecaused by the output capacitance Coss of the MOSFET. During each switching cycle the energystored in Coss is dissipated in the MOSFET. Thus, for high switching frequency, a small Cossis preferred. The equations for switching and conduction losses are [23] [34]:

Pswitching = 12 · Coss · V

2DS · fswitch (2-12)

Pconduction = RDS(on) · I2DS(rms) (2-13)

IDS(rms) = Ip,peak ·

√D

3 (2-14)

Plosses = Pswitching + Pconduction (2-15)

With the considerations mentioned above, the AUIRFR4620 MOSFET was selected. This powerMOSFET is automotive qualified to Infineon standards, which makes it low in switching andconduction losses thus making it good for fast switching and operating at high temperatures[14]. It is also rated for repetitive avalanche, which allows the MOSFET to dispense the surgevoltage into heat. Together these features contributes to overall system robustness. The relevantdatasheet values are the following [29]:

• VDSS = 200V

• ID = 24A

• RDS(on) = 64mΩ

• Coss = 125pF

• VSD = 1.3V

• Operating Temperature of 175 °C

• VGS(max) = ±20V with Vth = 3-5V


2.2 Components 13

Compared to other power MOSFETs in this VDSS range the AUIRFR4620 has a low outputcapacitance Coss, yet retains a reasonable Rds(on), leading to lower switching losses consideringthat the system would be switching at medium-high frequency. Using the functions 2-12, 2-13and 2-15 this leads to an estimated MOSFET loss of 1.6W assuming the system is running atmaximum power output, D = 0.49 and maximum switching frequency of 125 KHz.

Switching Circuit Design

However, a drawback of this MOSFET is that the body diode voltage is considerably high(1.3V). This leads to further losses on the secondary side of the flyback when the MOSFET isin flyback diode mode. To avoid this we placed a schottky-diode (V20202G-M3/4W) in parallelwith the MOSFET (figure 2-8) with a lower diode voltage drop of 0.71V. This way most of thecurrent flows through this diode instead of the inefficient MOSFET body diode.

Figure 2-8: Switching circuit adjustments with clamp and schottky

For further robustness of the system it is recommended to ensure that the power MOSFETswill not go into avalanche mode [24]. This is accomplished by adding a clamp circuit over thetransformer as shown in figure 2-8. The clamp circuitry considered for our flyback is a zenerdiode clamp because of its simplicity and amount of component. Clamp circuits absorb theparasitic excessive voltage produced by the leakage inductance. This is accomplished when theclamp diode (Dsn) turns on when Vclamp exceeds Vin + nV o. Vz (zener clamp voltage) shouldbe chosen based on a voltage Vmax, sufficiently lower than the maximum VDS of the MOSFETand the input voltage V in.

Vz = Vmax − Vin (2-16)

Making the power dissipated in the zener diode [24]:

Pz = 12Lleak · i

2peak ·

VclampVclamp − nVo

· fs (2-17)

Remarks

Figure 2-9:AUIRFR4620 [29]

Lastly, another factor to take into consideration while selecting a MOSFETis the body package. Different types of packages have their own character-istics. For our application a reasonable sized D-pak (2-9) was chosen dueto ease of prototyping, but choosing smaller packages can result in betterefficiency performance. Heat dissipation is also something to acknowledge,MOSFETs performance decreases and becomes less efficient at high tem-peratures. The AUIRFR4620 however has a high operating temperatureof 175 °C and a heat sink was not considered necessary in this design,although the option to add one later on has been left open.


2.2 Components 14

2.2.3 Integrated Circuit PWM controller

There are multiple ways to implement the control of the converter’s MOSFETs. One is byusing a microcontroller, performing voltage and current measurements and generating a PWMsignal based on a PI-controller. The upside of this approach is the degree of freedom when onewrites their own code and control loop, and having the ability to use the microcontroller’s otherperipherals like I2C, UART, etc. for direct communication, feedback and in-circuit debugging.

Another approach is to use an Integrated Circuit (IC) PWM controller. An IC PWM controlleris basically a hardware implementation of a certain control-loop, designed to perform one spe-cific task. The upside in this case is that the entire flyback converter control can be implementedthrough a single, purchasable IC, and thus reducing the complexity of the control circuit sig-nificantly as compared to the microcontroller realization. Therefore, the choice has been madeto design our converter with an IC as controlling element. The complexity of the converter andthe available time played an important role in the decision. With the IC implementation theconverter can be controlled with just a few analog signals that any microcontroller or develop-ment board is able to interpret and generate, thus creating a very robust and accessible flybackconverter with power management capability.

Requirements

The IC is a crucial component in the design, since it performs all measurements and control ofthe MOSFETs. The IC must be well-chosen in combination with the switching component, asthe collaboration of these two components form the basis of the control system. The IC must bestable, reliable, efficient and easy to control. As the component choice in this case is generally notsubject to fundamentally different operating approaches, the IC choice is determined by othercharacteristics with respect to; control method, working frequencies, operating temperatures,voltage limits and IC packaging, which are variable for each manufacturer and product family.Some actual requirements are:

• Vcc must be above the gate threshold of the MOSFET (req).

• Operating mode must be compatible with our bi-directional flyback topology (req).

• IC must be compatible with the switching of a low-side FET (req).

Design

When seeking for suitable IC’s one starts with narrowing the search to a control method appli-cable to the desired converter topology. For our flyback converter topology the available controlmethods are: Current control, Voltage control, Feed Forward control, Valley Current controland Peak Current control [17]. All of these methods can be used to control our circuit, so thechoice was based on the stability, complexity and accessibility of the control IC. Both currentand voltage control are proven, reliable control methods as they are the oldest and most usedmethods in SMPS design, based on simple PID control loops. Feed Forward is a more recentcontrol method that builds upon the classical PID-controller by adding terms that predict thebehaviour of the converter, making the controller proactive instead of reactive. Lastly, Peakcurrent control and Valley current control are two methods that add extra features to the es-tablished current-mode control method. Peak current control features an extra control loopbased on trailing-edge modulation that senses the current through the inductor and allows ananalog signal to set the maximum allowed current. Valley current control adds loss-less currentsensing and a leading-edge modulation control loop that makes it suitable for high frequency,


2.2 Components 15

high current buck conversion with small duty cycle variation.

Figure 2-10: PDIP-8 IC

For our converter the peak current control method is an excel-lent choice. It implements the standard control needed for normalconverter operation, and adds current limiting in a robust andaccessible manner. Now that the search has been limited to fly-back topology, peak current control IC’s the choice lies with thelast parameters regarding switching frequency, Vin, Vout, gatedrive current, and duty cycle limits. Our switching frequency,Vin and Vout are reasonably standard values and any IC will becompatible. Furthermore, the gate drive current does not have tobe very large as the MOSFET does not require it when switchedin the electrical circumstances of our converter. Lastly, the dutycycle maximum is an added feature that limits the duty cycle to apredetermined value. Choosing this value at 50% is a convenientaddition to the converter as it reduces the converter behaviourto purely Discontinuous Current Mode (DCM).

With these design parameters the UCx84x family seemed promising. The final choice landedon the UC2845 by Texas Instruments due to its duty cycle limit, operating temperature andturn-on voltage, making the converter suitable for voltages as low as 12V, which is the standardbattery voltage level.

Remarks

The PWM controller IC is a good choice for fast, analog control of our flyback converter.However, care must be taken when designing a PCB because the analog control circuitry issensitive to noise and consists of a few critical current paths.


2.3 Topology Design 16

2.3 Topology Design

Keeping all previously mentioned subjects in mind, the final converter topology has been de-signed and the schematic can be found in figure 2-11. The entire schematic, together with allsubsystems is depicted in appendix A figure A-1. The essential components needed for thebi-directional functioning of a flyback converter are all present in the form of the transformer,the MOSFETs and capacitors C19/C22.

The switching of the MOSFET introduces noise onto the input and output voltage lines, addi-tional capacitors (C20,C21,C23,C24) have therefore been added to function as high-frequencynoise paths to stabilize the output, as well as increase accuracy of the measurements [33].

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

D D

C C

B B

A A

Title

Number RevisionSizeA3

Date: 20/06/2017 Sheet ofFile: C:\Users\..\BEP_BiDirectionalFlyback.SchDocDrawn By:

6.8K

R29

2.2nFC37

R28

C31

C33

Q3

12V

R35R34

C365V

0.01ΩR23

1k

R18

1nFC28

Imeas1

Imeas1

R48R47

C455V

0.01ΩR24

1k

R19

1nFC27

Imeas2

Imeas2

300kR11

30kR17

300kR13

30kR21

300kR10

30kR16

300kR12

30kR20

47pFC21

47pFC20

47pFC24

47pFC23Vsense1.1

Vsense2.1

Vsense2.1820uFC22

R44

C43

C44

6.8K

R45

2.2nFC46

Q4Vsense1.1

12V

R27ILim

R40ILim

20k

R46Vsetp

20k

R30Vsetp

GateOut1

GateOut2

Vsense1.2Vsense2.2

100kR33

100kR43

5V

6.7uF C38

6.7uF C47

1KR39 2.2K

R36DIR

ON/OFF2

ON/OFF1

ON/OFF2

ON/OFF1

Vref1

Vref2

Vref2

Vref1

10KR25

Vsense1.2100nF

C30

5V

5V

10KR37

Vsense2.2100nF

C39

Vout1

Vout2

V1+

V1-

V2+

V2-

Direction ComparatorCurrent Mode Control Circuit

VsetpPWM

ILimPWM

5V

5V

1K

R8

1K

R22

330nFC29

330nFC18

Vsetp

ILim

DAC's

Isense2

Isense1

5V

5V

Imeas1

Imeas2

R42

C41R41

R32C34

R31

10K

R26

10K

R38

100nFC32

100nFC40

Iout1

Iout2

Measurement Bridge

Bi-Directional Flyback Converter Topology

10Ω

R14

10Ω

R15GateOut1

GateOut2

V1

Bi-Directional Flyback Converter - Groep B

Transformer

V1+

V2+L1 12V

C5C4C3 C8

Power Distribution

3

21

84 U4A

MCP602-I/P

3

21

84 U5A

MCP602-I/P

75

6

84 U4B

MCP602-I/P

75

6

84 U5B

MCP602-I/P

3

21

84

U7A

3

21

84

U8A

330uFC2

C7

12

V1

12

V2

V1+V1-

V2-V2+

820uFC19

1 23 45 67 89 1011 1213 14

Control Signals

Header 7X2

Vout1Vout2Iout1Iout2VsetpPWMILimPWMDIR

Connectors

C48 C49 C50

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U6

UC2845N

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U9

UC2845N

31

84

2 1 U12ALM393P

6

572

84

U12BLM393P

5V

5V

31

84

2 1U3ALM393P

6

572

84

U3BLM393P

1V56

1V56

1V56

2.7k R9

2.7kR7

5V

D69

12V

V1 V2

Gate1 Gate2

GND1 GND6

DIR1

DIR2

Vsetp

ILim

1MR49

1MR50

5V

GND2 GND3 GND4GND5

D10LED1

R51

GateOut1 GateOut2

5V

V1-Shield S

VCC 1D- 2

D+ 3GND 4

J1

USB B

R52R53

R54

VsetpPWMILimPWM

DIR

5V

Input1G

ND

3

ON

/OFF

5

Output 2

Feedback 4

U2 LM2575HVT-12

100uFC10

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U1 LM2575HVT-5

100uFC1

330uFC9

L2 PI5V01 CO5V

PI12V01 CO12V

PIC101

PIC102 COC1 PIC201 PIC202

COC2 PIC301

PIC302 COC3 PIC401

PIC402 COC4 PIC501

PIC502 COC5

PIC701 PIC702 COC7 PIC801

PIC802 COC8

PIC901 PIC902

COC9 PIC1001

PIC1002 COC10

PIC1801

PIC1802 COC18

PIC1901

PIC1902

COC19

PIC2001

PIC2002 COC20

PIC2101

PIC2102 COC21 PIC2201

PIC2202

COC22 PIC2301

PIC2302 COC23

PIC2401

PIC2402 COC24

PIC2701

PIC2702 COC27

PIC2801

PIC2802 COC28

PIC2901

PIC2902 COC29

PIC3001


COC31

PIC3201

PIC3202 COC32

PIC3301 PIC3302

COC33

PIC3401 PIC3402 COC34

PIC3601 PIC3602

COC36

PIC3701

PIC3702 COC37

PIC3801

PIC3802 COC38

PIC3901

PIC3902 COC39

PIC4001

PIC4002 COC40


PIC4301 PIC4302

COC43

PIC4401 PIC4402

COC44

PIC4501 PIC4502

COC45

PIC4601

PIC4602 COC46

PIC4701 PIC4702

COC47

PIC4801



PIC5002 COC50

PIControl Signals01 PIControl Signals02







COControl Signals

PID101 PID102

COD1

PID201 PID202

COD2

PID301 PID302

COD3

PID401 PID402

COD4

PID501 PID502

COD5

PID601 PID602

COD6

PID701 PID702

COD7

PID801 PID802

COD8 PID901 PID902

COD9

PID1001 PID1002

COD10 PID1101 PID1102

COD11

PID6901 PID6902

COD69

PIDIR101 CODIR1

PIDIR201 CODIR2

PIGate101 COGate1

PIGate201 COGate2

PIGND101 COGND1

PIGND201 COGND2

PIGND301 COGND3

PIGND401 COGND4

PIGND501 COGND5

PIGND601 COGND6

PIILim01 COILim

PIInput01

COInput

PIJ101

PIJ102

PIJ103

PIJ104

PIJ10S

COJ1

PIL101 PIL102

COL1 PIL201 PIL202

COL2

PIQ101 PIQ102

PIQ103 COQ1

PIQ201 PIQ202

PIQ203 COQ2

PIQ301 PIQ302

PIQ303

COQ3

PIQ401 PIQ402

PIQ403

COQ4

PIR701

PIR702

COR7

PIR801 PIR802

COR8

PIR901

PIR902

COR9

PIR1001

PIR1002 COR10

PIR1101

PIR1102 COR11

PIR1201

PIR1202 COR12

PIR1301

PIR1302 COR13

PIR1401 PIR1402

COR14 PIR1501 PIR1502

COR15

PIR1601

PIR1602 COR16

PIR1701

PIR1702 COR17

PIR1801 PIR1802


COR19 PIR2001

PIR2002 COR20

PIR2101

PIR2102 COR21

PIR2201 PIR2202

COR22

PIR2301

PIR2302 COR23

PIR2401

PIR2402 COR24

PIR2501 PIR2502

COR25

PIR2601 PIR2602 COR26


PIR2801 PIR2802


COR29

PIR3001 PIR3002

COR30 PIR3101 PIR3102 COR31

PIR3201 PIR3202

COR32

PIR3301

PIR3302

COR33

PIR3401 PIR3402


COR35

PIR3601 PIR3602

COR36

PIR3701 PIR3702

COR37


PIR3901

PIR3902

COR39

PIR4001 PIR4002

COR40


PIR4201 PIR4202

COR42

PIR4301

PIR4302 COR43

PIR4401 PIR4402


COR45




PIR4901

PIR4902

COR49 PIR5001

PIR5002

COR50

PIR5101

PIR5102 COR51

PIR5201

PIR5202

COR52 PIR5301

PIR5302

COR53 PIR5401

PIR5402

COR54

PITransformer00

PITransformer01

PITransformer02

PITransformer03 COTransformer

PIU101 PIU102

PIU103

PIU104

PIU105

COU1

PIU201 PIU202

PIU203

PIU204

PIU205

COU2

PIU301

PIU302

PIU303

PIU304

PIU308

COU3A

PIU304

PIU305

PIU306

PIU307

PIU308

COU3B

PIU401

PIU402

PIU403

PIU404

PIU408

COU4A

PIU404 PIU405

PIU406

PIU407

PIU408

COU4B

PIU501

PIU502

PIU503

PIU504

PIU508

COU5A

PIU504 PIU505

PIU506

PIU507

PIU508

COU5B

PIU601

PIU602 PIU603

PIU604

PIU605

PIU606

PIU607

PIU608

COU6

PIU701

PIU702

PIU703

PIU704

PIU708 COU7A

PIU801

PIU802

PIU803

PIU804

PIU808 COU8A

PIU901

PIU902 PIU903

PIU904

PIU905

PIU906

PIU907

PIU908

COU9

PIU1201

PIU1202

PIU1203

PIU1204

PIU1208

COU12A

PIU1204

PIU1205

PIU1206

PIU1207

PIU1208

COU12B

PIV101 COV1

PIV101

PIV102

PIV201 COV2

PIV201

PIV202

PIVsetp01 COVsetp

PIR3602 PIR3901

PIU302

PIU306

PIU1202

PIU1205

NL1V56

PI5V01

PIC302 PIC402 PIC502 PIC701 PIC802 PIC901 PIC4802 PIC4902 PIC5002

PIJ101

PIL202

PIR701

PIR901

PIR3302 PIR3601

PIR4302

PIR5101

PIR5302

PIU104

PIU308

PIU408

PIU508

PIU708

PIU808

PIU1208

NL5V

PI12V01 PIC201

PIC3801

PIC4701

PIL102

PIU204

PIU607

PIU907


PIR5401

PIU1203

PIU1206

NLDIR

PIGate101

PIR1401

PIU606

NLGateOut1 PIGate201

PIR1502

PIU906

NLGateOut2

PIC2902

PIILim01 PIR2201

PIR2702

PIR4002

NLILim


PIR5301

PIU305

NLILimPWM

PIC2802 PIR1802

PIR2701

PIU405

PIU703

NLImeas1

PIC2702 PIR1901

PIR4001

PIU505

PIU803

NLImeas2

PIC3202


PIR2602 NLIout1

PIC4002


PIR3802 NLIout2

PIC3602

PIQ303

PIR3401

PIU603 PIU701

NLIsense1

PIC4501

PIQ403

PIR4701

PIU801 PIU903

NLIsense2

PIC101 PIC1001

PID102

PID202

PIInput01

PIU101

PIU201

PIC3002 PIR2501 PIU403

PIC3102

PIC3302

PIU601

PIC3301 PIR2801

PIC3401

PIR3102 PIR3201

PIU406

PIC3402

PIR2601

PIR3202

PIU407

PIC3601

PIR3402 PIR3501

PIU702

PIC3702

PIR2902

PIU604


PIC4101

PIR4102 PIR4201

PIU506

PIC4102

PIR3801

PIR4202

PIU507

PIC4302

PIC4402

PIU901

PIC4401 PIR4401

PIC4502

PIR4702 PIR4801

PIU802

PIC4602

PIR4502

PIU904

PID302 PIL101 PIU202

PID401

PID602 PIQ101 PITransformer02 PID402

PID802 PID501


PID902

PID601 PIQ103 PIR1801

PIR2302


PIR2402

PID1001 PIR5102


PIJ102

PIJ103

PIJ104

PIQ102

PIR1402

PIR5001 PIQ202

PIR1501

PIR4901

PIR702 PIR802 PIU301


PIDIR101 PIQ302

PIR3301 PIU1201

NLON0OFF1

PIDIR201 PIQ402

PIR4301

PIU1207 NLON0OFF2

PIC1901 PIC2002 PIC2102

PID101

PID801

PIR1002 PIR1102

PITransformer03 PIV101

PIV102 NLV10

PIC2201 PIC2302 PIC2402

PID201

PID901

PIR1202 PIR1302

PITransformer01

PIV201 NLV20

PIC102 PIC202

PIC301 PIC401 PIC501 PIC702 PIC801 PIC902 PIC1002

PIC1801

PIC1902 PIC2001 PIC2101 PIC2202

PIC2301 PIC2401

PIC2701 PIC2801 PIC2901

PIC3001 PIC3201

PIC3701

PIC3802

PIC3901 PIC4001

PIC4601 PIC4702

PIC4801 PIC4901 PIC5001 PID301 PID1002

PID1101

PID6901

PIGND101 PIGND201 PIGND301 PIGND401 PIGND501 PIGND601

PIJ10S

PIR1601 PIR1701 PIR2001 PIR2101

PIR2301 PIR2401

PIR3101

PIR3502

PIR3902

PIR4101

PIR4802

PIR4902 PIR5002

PIR5202 PIR5402

PIU103 PIU105 PIU203 PIU205

PIU304

PIU404

PIU504 PIU605

PIU704

PIU804

PIU905

PIU1204

PIV101

PIV202

NLV10

NLV20


PIU401

PIU402

NLVout1


PIU501

PIU502

NLVout2

PIQ301

PIR2901 PIU608

NLVref1

PIQ401

PIR4501 PIU908

NLVref2

PIC4301

PIR1001

PIR1602

PIR4402

PIR4602

PIU902

NLVsense101 PIR1101

PIR1702

PIR2502

NLVsense102 PIC3101

PIR1201

PIR2002

PIR2802

PIR3002

PIU602

NLVsense201

PIR1301

PIR2102

PIR3702

NLVsense202

PIC1802 PID6902 PIR801

PIR3001

PIR4601

PIVsetp01 NLVsetp


PIR5201

PIU303

NLVsetpPWM

Figure 2-11: Bi-Directional flyback converter topology

R14/R15 are two small resistors added to the MOSFET gates to limit the current on thesepaths from PWM controller to MOSFET. R50/R49 are two large resistors connected from theMOSFET gates to ground to function as a pull-down path when the MOSFET gate signal isleft floating.

The Schottky diodes discussed in section 2.2.2 are present in the design as well.

Voltage measurement Four resistor divider networks (R10/R16, R11/R17, R12/R20, R13/R21)have been added to the V1 and V2 rails to function as voltage measurements. The 300K-30Kdivider ensures that the entire input and output voltage range gets divided by ten to make itusable for the microcontroller and the other subsystems. (12V-48V → 1.2V-4.8V)

Current measurement R23 and R24 are two shunt resistors placed between the source of theMOSFETs and GND, and are used for measuring the primary and secondary current. Since theresistance is so small, all of the current through the MOSFETs will pass through these resistorsto ground. The current through the shunts creates a potential difference over the resistors whichis directly proportional to the current passing through, making it an ideal place to measure thecurrent. The voltage over the resistor however, is very small compared to the noise of the powerline. To counter this, a small low-pass filter (R18/C28 and R19/C27) has been attached to bothcurrent measurements to filter out some of this noise.


2.4 Subsystems 17

2.4 Subsystems

2.4.1 Peak Current Mode Controller

The PWM control IC needs some components to be able to function[30]. Figure 2-12 shows thedesign from our Altium schematic. Both IC circuits are identical, and are the foundation of thebi-directional nature of the converter as they each control one MOSFET. The transistors Q3and Q4 control which IC is being used, and thus controlling the direction of the energy flow.

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

D D

C C

B B

A A

Title



6.8K

R29

2.2nFC37

R28

C31

C33

Q3

12V

R35R34

C365V

0.01ΩR23

1k

R18

1nFC28

Imeas1

Imeas1

R48R47

C455V

0.01ΩR24

1k

R19

1nFC27

Imeas2

Imeas2

300kR11

30kR17

300kR13

30kR21

300kR10

30kR16

300kR12

30kR20

47pFC21

47pFC20

47pFC24

47pFC23Vsense1.1

Vsense2.1

Vsense2.1820uFC22

R44

C43

C44

6.8K

R45

2.2nFC46

Q4Vsense1.1

12V

R27ILim

R40ILim

20k

R46Vsetp

20k

R30Vsetp

GateOut1

GateOut2

Vsense1.2Vsense2.2

100kR33

100kR43

5V

6.7uF C38

6.7uF C47

1KR39 2.2K

R36DIR

ON/OFF2

ON/OFF1

ON/OFF2

ON/OFF1

Vref1

Vref2

Vref2

Vref1

10KR25

Vsense1.2100nF

C30

5V

5V

10KR37

Vsense2.2100nF

C39

Vout1

Vout2

V1+

V1-

V2+

V2-


VsetpPWM

ILimPWM

5V

5V

1K

R8

1K

R22

330nFC29

330nFC18

Vsetp

ILim

DAC's

Isense2

Isense1

5V

5V

Imeas1

Imeas2

R42

C41R41

R32C34

R31

10K

R26

10K

R38

100nFC32

100nFC40

Iout1

Iout2

Measurement Bridge


10Ω

R14

10Ω

R15GateOut1

GateOut2

V1


Transformer

V1+

V2+L1 12V

C5C4C3 C8

Power Distribution

3

21

84 U4A

MCP602-I/P

3

21

84 U5A

MCP602-I/P

75

6

84 U4B

MCP602-I/P

75

6

84 U5B

MCP602-I/P

3

21

84

U7A

3

21

84

U8A

330uFC2

C7

12

V1

12

V2

V1+V1-

V2-V2+

820uFC19

1 23 45 67 89 1011 1213 14

Control Signals

Header 7X2


Connectors

C48 C49 C50

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U6

UC2845N

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U9

UC2845N

31

84

2 1 U12ALM393P

6

572

84

U12BLM393P

5V

5V

31

84

2 1U3ALM393P

6

572

84

U3BLM393P

1V56

1V56

1V56

2.7k R9

2.7kR7

5V

D69

12V

V1 V2

Gate1 Gate2

GND1 GND6

DIR1

DIR2

Vsetp

ILim

1MR49

1MR50

5V

GND2 GND3 GND4GND5

D10LED1

R51

GateOut1 GateOut2

5V

V1-Shield S

VCC 1D- 2

D+ 3GND 4

J1

USB B

R52R53

R54

VsetpPWMILimPWM

DIR

5V

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U2 LM2575HVT-12

100uFC10

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U1 LM2575HVT-5

100uFC1

330uFC9

L2 PI5V01 CO5V

PI12V01 CO12V

PIC101


COC2 PIC301

PIC302 COC3 PIC401

PIC402 COC4 PIC501

PIC502 COC5


PIC802 COC8

PIC901 PIC902

COC9 PIC1001

PIC1002 COC10

PIC1801

PIC1802 COC18

PIC1901

PIC1902

COC19

PIC2001

PIC2002 COC20

PIC2101


PIC2202

COC22 PIC2301

PIC2302 COC23

PIC2401

PIC2402 COC24

PIC2701

PIC2702 COC27

PIC2801

PIC2802 COC28

PIC2901

PIC2902 COC29

PIC3001


COC31

PIC3201

PIC3202 COC32

PIC3301 PIC3302

COC33


PIC3601 PIC3602

COC36

PIC3701

PIC3702 COC37

PIC3801

PIC3802 COC38

PIC3901

PIC3902 COC39

PIC4001

PIC4002 COC40


PIC4301 PIC4302

COC43

PIC4401 PIC4402

COC44

PIC4501 PIC4502

COC45

PIC4601

PIC4602 COC46

PIC4701 PIC4702

COC47

PIC4801



PIC5002 COC50








COControl Signals

PID101 PID102

COD1

PID201 PID202

COD2

PID301 PID302

COD3

PID401 PID402

COD4

PID501 PID502

COD5

PID601 PID602

COD6

PID701 PID702

COD7

PID801 PID802

COD8 PID901 PID902

COD9

PID1001 PID1002


COD11

PID6901 PID6902

COD69

PIDIR101 CODIR1

PIDIR201 CODIR2

PIGate101 COGate1

PIGate201 COGate2

PIGND101 COGND1

PIGND201 COGND2

PIGND301 COGND3

PIGND401 COGND4

PIGND501 COGND5

PIGND601 COGND6

PIILim01 COILim

PIInput01

COInput

PIJ101

PIJ102

PIJ103

PIJ104

PIJ10S

COJ1

PIL101 PIL102

COL1 PIL201 PIL202

COL2

PIQ101 PIQ102

PIQ103 COQ1

PIQ201 PIQ202

PIQ203 COQ2

PIQ301 PIQ302

PIQ303

COQ3

PIQ401 PIQ402

PIQ403

COQ4

PIR701

PIR702

COR7

PIR801 PIR802

COR8

PIR901

PIR902

COR9

PIR1001

PIR1002 COR10

PIR1101

PIR1102 COR11

PIR1201

PIR1202 COR12

PIR1301

PIR1302 COR13

PIR1401 PIR1402


COR15

PIR1601

PIR1602 COR16

PIR1701

PIR1702 COR17

PIR1801 PIR1802


COR19 PIR2001

PIR2002 COR20

PIR2101

PIR2102 COR21

PIR2201 PIR2202

COR22

PIR2301

PIR2302 COR23

PIR2401

PIR2402 COR24

PIR2501 PIR2502

COR25



PIR2801 PIR2802


COR29

PIR3001 PIR3002


PIR3201 PIR3202

COR32

PIR3301

PIR3302

COR33

PIR3401 PIR3402


COR35

PIR3601 PIR3602

COR36

PIR3701 PIR3702

COR37


PIR3901

PIR3902

COR39

PIR4001 PIR4002

COR40


PIR4201 PIR4202

COR42

PIR4301

PIR4302 COR43

PIR4401 PIR4402


COR45




PIR4901

PIR4902

COR49 PIR5001

PIR5002

COR50

PIR5101

PIR5102 COR51

PIR5201

PIR5202

COR52 PIR5301

PIR5302

COR53 PIR5401

PIR5402

COR54

PITransformer00

PITransformer01

PITransformer02


PIU101 PIU102

PIU103

PIU104

PIU105

COU1

PIU201 PIU202

PIU203

PIU204

PIU205

COU2

PIU301

PIU302

PIU303

PIU304

PIU308

COU3A

PIU304

PIU305

PIU306

PIU307

PIU308

COU3B

PIU401

PIU402

PIU403

PIU404

PIU408

COU4A

PIU404 PIU405

PIU406

PIU407

PIU408

COU4B

PIU501

PIU502

PIU503

PIU504

PIU508

COU5A

PIU504 PIU505

PIU506

PIU507

PIU508

COU5B

PIU601

PIU602 PIU603

PIU604

PIU605

PIU606

PIU607

PIU608

COU6

PIU701

PIU702

PIU703

PIU704

PIU708 COU7A

PIU801

PIU802

PIU803

PIU804

PIU808 COU8A

PIU901

PIU902 PIU903

PIU904

PIU905

PIU906

PIU907

PIU908

COU9

PIU1201

PIU1202

PIU1203

PIU1204

PIU1208

COU12A

PIU1204

PIU1205

PIU1206

PIU1207

PIU1208

COU12B

PIV101 COV1

PIV101

PIV102

PIV201 COV2

PIV201

PIV202

PIVsetp01 COVsetp

PIR3602 PIR3901

PIU302

PIU306

PIU1202

PIU1205

NL1V56

PI5V01


PIJ101

PIL202

PIR701

PIR901

PIR3302 PIR3601

PIR4302

PIR5101

PIR5302

PIU104

PIU308

PIU408

PIU508

PIU708

PIU808

PIU1208

NL5V

PI12V01 PIC201

PIC3801

PIC4701

PIL102

PIU204

PIU607

PIU907


PIR5401

PIU1203

PIU1206

NLDIR

PIGate101

PIR1401

PIU606


PIR1502

PIU906

NLGateOut2

PIC2902

PIILim01 PIR2201

PIR2702

PIR4002

NLILim


PIR5301

PIU305

NLILimPWM

PIC2802 PIR1802

PIR2701

PIU405

PIU703

NLImeas1

PIC2702 PIR1901

PIR4001

PIU505

PIU803

NLImeas2

PIC3202


PIR2602 NLIout1

PIC4002


PIR3802 NLIout2

PIC3602

PIQ303

PIR3401

PIU603 PIU701

NLIsense1

PIC4501

PIQ403

PIR4701

PIU801 PIU903

NLIsense2

PIC101 PIC1001

PID102

PID202

PIInput01

PIU101

PIU201


PIC3102

PIC3302

PIU601

PIC3301 PIR2801

PIC3401

PIR3102 PIR3201

PIU406

PIC3402

PIR2601

PIR3202

PIU407

PIC3601

PIR3402 PIR3501

PIU702

PIC3702

PIR2902

PIU604


PIC4101

PIR4102 PIR4201

PIU506

PIC4102

PIR3801

PIR4202

PIU507

PIC4302

PIC4402

PIU901

PIC4401 PIR4401

PIC4502

PIR4702 PIR4801

PIU802

PIC4602

PIR4502

PIU904


PID401


PID802 PID501


PID902


PIR2302


PIR2402

PID1001 PIR5102


PIJ102

PIJ103

PIJ104

PIQ102

PIR1402

PIR5001 PIQ202

PIR1501

PIR4901



PIDIR101 PIQ302

PIR3301 PIU1201

NLON0OFF1

PIDIR201 PIQ402

PIR4301

PIU1207 NLON0OFF2

PIC1901 PIC2002 PIC2102

PID101

PID801

PIR1002 PIR1102


PIV102 NLV10

PIC2201 PIC2302 PIC2402

PID201

PID901

PIR1202 PIR1302

PITransformer01

PIV201 NLV20

PIC102 PIC202


PIC1801

PIC1902 PIC2001 PIC2101 PIC2202

PIC2301 PIC2401

PIC2701 PIC2801 PIC2901

PIC3001 PIC3201

PIC3701

PIC3802

PIC3901 PIC4001

PIC4601 PIC4702


PID1101

PID6901


PIJ10S

PIR1601 PIR1701 PIR2001 PIR2101

PIR2301 PIR2401

PIR3101

PIR3502

PIR3902

PIR4101

PIR4802

PIR4902 PIR5002

PIR5202 PIR5402


PIU304

PIU404

PIU504 PIU605

PIU704

PIU804

PIU905

PIU1204

PIV101

PIV202

NLV10

NLV20


PIU401

PIU402

NLVout1


PIU501

PIU502

NLVout2

PIQ301

PIR2901 PIU608

NLVref1

PIQ401

PIR4501 PIU908

NLVref2

PIC4301

PIR1001

PIR1602

PIR4402

PIR4602

PIU902

NLVsense101 PIR1101

PIR1702

PIR2502

NLVsense102 PIC3101

PIR1201

PIR2002

PIR2802

PIR3002

PIU602

NLVsense201

PIR1301

PIR2102

PIR3702

NLVsense202


PIR3001

PIR4601

PIVsetp01 NLVsetp


PIR5201

PIU303

NLVsetpPWM

Figure 2-12: Peak Current mode control circuit implementation with UC2845

RT/CT The RT/CT pin of the IC determines the operating frequency of the IC. The resistorand capacitor implementation of R29/C37 and R45/C46 set the IC operating frequency to 125KHz.

ISENSE The voltage over the shunt resistor is measured and fed into the control circuitthrough connections Imeas1 and Imeas2. The shunt resistor has a value of 0.01Ω, meaningthat a peak current of 20A results in a voltage of 0.2V over the shunt. The IC uses a max.1V reference voltage, to which it compares ISENSE to determine the maximum current. Thismeans an amplifying op-amp circuit is needed to scale the shunt resistor voltage range to max.1V. This is implemented by U7A and U8A respectively for each side, operating in non-invertingtopology. C36 and C45 are added to the feedback network to function as an active low-pass filterto help reduce noise and increase accuracy. The analog current limit signal ILim, originatingfrom the microcontroller, is super-positioned onto the current measurement through resistorsR27 and R40. This raises the voltage level of the current measurement higher than it actuallyis, tricking the IC into detecting max current and switching off the MOSFET while the actualcurrent is not actually maximum.


2.4 Subsystems 18

VFB/COMP These pins function as voltage measurements and control inputs. The resistordivided voltage of the output (Vout) is fed into the control circuit through connections Vsense1.1and Vsense2.1. The components placed between VFB and COMP determine the transfer func-tion of the error amplifier feedback network. The type of compensation and its influence willbe discussed in section 3. The analog input signal Vsetp, originating from the microcontroller,is super-positioned onto the VFB pin through resistors R30 and R46. If no voltage is appliedonto VFB (leave out Vsetp and R30), the IC will try to regulate the output voltage so that theVFB pin equals the standard internal value of 2.5V. Depending on the resistor divider ratio onthe output this results in a fixed Vout. By adding Vsetp, VFB is pushed above or below 2.5V,meaning the IC will regulate the output voltage until VFB is back to 2.5V. Since the resistordivider on the output is no longer a standard 2 resistor network, but has another resistor andan analog signal in the structure (Vsetp and R30/R46), the 2.5V at VFB no longer correspondsto only one fixed Vout, but can be any voltage that is within the macro-circuit design parameters.

The OUTPUT pin is the signal that goes to the MOSFET gate. This is either 0 V, whenthe MOSFET should be closed, or VCC (12V) when the MOSFET should be open. The signalis fed through a 10Ω resistor to limit the current spikes of the IC and increase the switchingstability.

C38 and C47 function as a local energy buffer for the IC’s. When the gate signal is switchedfrom low to high, peak currents up to 1A can flow because the IC wants to turn the MOSFETon as fast as possible. Instead of building a power supply capable of delivering 2 × 1A to theIC’s, the capacitors provide the necessary peak current. The IC’s are decoupled from the supplyand no longer rely on it for high peak current. A smaller power supply can be used. It is ofimportance that the capacitor is big enough to provide the current for as long as needed percycle, whilst also retaining the voltage level of VCC. Choose the capacitor too large though,and the start-up time and current draw increases rapidly.


2.4 Subsystems 19

2.4.2 Measurement Bridge

The measurement bridge is the section of the converter that translates the converter’s noisy,analog signals into steady DC signals that the microcontroller can sample with its ADC. Themeasurements that are of interest to the microcontroller are the voltage and current on bothsides of the converter. Figure 2-13 shows the op-amp implementation of these measurements.To measure the voltage, a resistor divider has been placed on both sides of the converter’s powertraces. This signal is passed to the measurement bridge through Vsense1.2 and Vsense2.2, andfed to voltage-followers U4A and U5A. Note that this is a different resistor divider networkas is used for the IC voltage measurement. This is done because the IC forces its resistordivider to 2.5V, thus rendering it useless for the purpose of voltage sensing off-board. R25/C30and R37/C39 form a passive low-pass filter (LPF). This is implemented to filter out the highfrequency switching noise that the converter introduces onto the high-power path.

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

D D

C C

B B

A A

Title



6.8K

R29

2.2nFC37

R28

C31

C33

Q3

12V

R35R34

C365V

0.01ΩR23

1k

R18

1nFC28

Imeas1

Imeas1

R48R47

C455V

0.01ΩR24

1k

R19

1nFC27

Imeas2

Imeas2

300kR11

30kR17

300kR13

30kR21

300kR10

30kR16

300kR12

30kR20

47pFC21

47pFC20

47pFC24

47pFC23Vsense1.1

Vsense2.1

Vsense2.1820uFC22

R44

C43

C44

6.8K

R45

2.2nFC46

Q4Vsense1.1

12V

R27ILim

R40ILim

20k

R46Vsetp

20k

R30Vsetp

GateOut1

GateOut2

Vsense1.2Vsense2.2

100kR33

100kR43

5V

6.7uF C38

6.7uF C47

1KR39 2.2K

R36DIR

ON/OFF2

ON/OFF1

ON/OFF2

ON/OFF1

Vref1

Vref2

Vref2

Vref1

10KR25

Vsense1.2100nF

C30

5V

5V

10KR37

Vsense2.2100nF

C39

Vout1

Vout2

V1+

V1-

V2+

V2-


VsetpPWM

ILimPWM

5V

5V

1K

R8

1K

R22

330nFC29

330nFC18

Vsetp

ILim

DAC's

Isense2

Isense1

5V

5V

Imeas1

Imeas2

R42

C41R41

R32C34

R31

10K

R26

10K

R38

100nFC32

100nFC40

Iout1

Iout2

Measurement Bridge


10Ω

R14

10Ω

R15GateOut1

GateOut2

V1


Transformer

V1+

V2+L1 12V

C5C4C3 C8

Power Distribution

3

21

84 U4A

MCP602-I/P

3

21

84 U5A

MCP602-I/P

75

6

84 U4B

MCP602-I/P

75

6

84 U5B

MCP602-I/P

3

21

84

U7A

3

21

84

U8A

330uFC2

C7

12

V1

12

V2

V1+V1-

V2-V2+

820uFC19

1 23 45 67 89 1011 1213 14

Control Signals

Header 7X2


Connectors

C48 C49 C50

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U6

UC2845N

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U9

UC2845N

31

84

2 1 U12ALM393P

6

572

84

U12BLM393P

5V

5V

31

84

2 1U3ALM393P

6

572

84

U3BLM393P

1V56

1V56

1V56

2.7k R9

2.7kR7

5V

D69

12V

V1 V2

Gate1 Gate2

GND1 GND6

DIR1

DIR2

Vsetp

ILim

1MR49

1MR50

5V

GND2 GND3 GND4GND5

D10LED1

R51

GateOut1 GateOut2

5V

V1-Shield S

VCC 1D- 2

D+ 3GND 4

J1

USB B

R52R53

R54

VsetpPWMILimPWM

DIR

5V

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U2 LM2575HVT-12

100uFC10

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U1 LM2575HVT-5

100uFC1

330uFC9

L2 PI5V01 CO5V

PI12V01 CO12V

PIC101


COC2 PIC301

PIC302 COC3 PIC401

PIC402 COC4 PIC501

PIC502 COC5


PIC802 COC8

PIC901 PIC902

COC9 PIC1001

PIC1002 COC10

PIC1801

PIC1802 COC18

PIC1901

PIC1902

COC19

PIC2001

PIC2002 COC20

PIC2101


PIC2202

COC22 PIC2301

PIC2302 COC23

PIC2401

PIC2402 COC24

PIC2701

PIC2702 COC27

PIC2801

PIC2802 COC28

PIC2901

PIC2902 COC29

PIC3001


COC31

PIC3201

PIC3202 COC32

PIC3301 PIC3302

COC33


PIC3601 PIC3602

COC36

PIC3701

PIC3702 COC37

PIC3801

PIC3802 COC38

PIC3901

PIC3902 COC39

PIC4001

PIC4002 COC40


PIC4301 PIC4302

COC43

PIC4401 PIC4402

COC44

PIC4501 PIC4502

COC45

PIC4601

PIC4602 COC46

PIC4701 PIC4702

COC47

PIC4801



PIC5002 COC50








COControl Signals

PID101 PID102

COD1

PID201 PID202

COD2

PID301 PID302

COD3

PID401 PID402

COD4

PID501 PID502

COD5

PID601 PID602

COD6

PID701 PID702

COD7

PID801 PID802

COD8 PID901 PID902

COD9

PID1001 PID1002


COD11

PID6901 PID6902

COD69

PIDIR101 CODIR1

PIDIR201 CODIR2

PIGate101 COGate1

PIGate201 COGate2

PIGND101 COGND1

PIGND201 COGND2

PIGND301 COGND3

PIGND401 COGND4

PIGND501 COGND5

PIGND601 COGND6

PIILim01 COILim

PIInput01

COInput

PIJ101

PIJ102

PIJ103

PIJ104

PIJ10S

COJ1

PIL101 PIL102

COL1 PIL201 PIL202

COL2

PIQ101 PIQ102

PIQ103 COQ1

PIQ201 PIQ202

PIQ203 COQ2

PIQ301 PIQ302

PIQ303

COQ3

PIQ401 PIQ402

PIQ403

COQ4

PIR701

PIR702

COR7

PIR801 PIR802

COR8

PIR901

PIR902

COR9

PIR1001

PIR1002 COR10

PIR1101

PIR1102 COR11

PIR1201

PIR1202 COR12

PIR1301

PIR1302 COR13

PIR1401 PIR1402


COR15

PIR1601

PIR1602 COR16

PIR1701

PIR1702 COR17

PIR1801 PIR1802


COR19 PIR2001

PIR2002 COR20

PIR2101

PIR2102 COR21

PIR2201 PIR2202

COR22

PIR2301

PIR2302 COR23

PIR2401

PIR2402 COR24

PIR2501 PIR2502

COR25



PIR2801 PIR2802


COR29

PIR3001 PIR3002


PIR3201 PIR3202

COR32

PIR3301

PIR3302

COR33

PIR3401 PIR3402


COR35

PIR3601 PIR3602

COR36

PIR3701 PIR3702

COR37


PIR3901

PIR3902

COR39

PIR4001 PIR4002

COR40


PIR4201 PIR4202

COR42

PIR4301

PIR4302 COR43

PIR4401 PIR4402


COR45




PIR4901

PIR4902

COR49 PIR5001

PIR5002

COR50

PIR5101

PIR5102 COR51

PIR5201

PIR5202

COR52 PIR5301

PIR5302

COR53 PIR5401

PIR5402

COR54

PITransformer00

PITransformer01

PITransformer02


PIU101 PIU102

PIU103

PIU104

PIU105

COU1

PIU201 PIU202

PIU203

PIU204

PIU205

COU2

PIU301

PIU302

PIU303

PIU304

PIU308

COU3A

PIU304

PIU305

PIU306

PIU307

PIU308

COU3B

PIU401

PIU402

PIU403

PIU404

PIU408

COU4A

PIU404 PIU405

PIU406

PIU407

PIU408

COU4B

PIU501

PIU502

PIU503

PIU504

PIU508

COU5A

PIU504 PIU505

PIU506

PIU507

PIU508

COU5B

PIU601

PIU602 PIU603

PIU604

PIU605

PIU606

PIU607

PIU608

COU6

PIU701

PIU702

PIU703

PIU704

PIU708 COU7A

PIU801

PIU802

PIU803

PIU804

PIU808 COU8A

PIU901

PIU902 PIU903

PIU904

PIU905

PIU906

PIU907

PIU908

COU9

PIU1201

PIU1202

PIU1203

PIU1204

PIU1208

COU12A

PIU1204

PIU1205

PIU1206

PIU1207

PIU1208

COU12B

PIV101 COV1

PIV101

PIV102

PIV201 COV2

PIV201

PIV202

PIVsetp01 COVsetp

PIR3602 PIR3901

PIU302

PIU306

PIU1202

PIU1205

NL1V56

PI5V01


PIJ101

PIL202

PIR701

PIR901

PIR3302 PIR3601

PIR4302

PIR5101

PIR5302

PIU104

PIU308

PIU408

PIU508

PIU708

PIU808

PIU1208

NL5V

PI12V01 PIC201

PIC3801

PIC4701

PIL102

PIU204

PIU607

PIU907


PIR5401

PIU1203

PIU1206

NLDIR

PIGate101

PIR1401

PIU606


PIR1502

PIU906

NLGateOut2

PIC2902

PIILim01 PIR2201

PIR2702

PIR4002

NLILim


PIR5301

PIU305

NLILimPWM

PIC2802 PIR1802

PIR2701

PIU405

PIU703

NLImeas1

PIC2702 PIR1901

PIR4001

PIU505

PIU803

NLImeas2

PIC3202


PIR2602 NLIout1

PIC4002


PIR3802 NLIout2

PIC3602

PIQ303

PIR3401

PIU603 PIU701

NLIsense1

PIC4501

PIQ403

PIR4701

PIU801 PIU903

NLIsense2

PIC101 PIC1001

PID102

PID202

PIInput01

PIU101

PIU201


PIC3102

PIC3302

PIU601

PIC3301 PIR2801

PIC3401

PIR3102 PIR3201

PIU406

PIC3402

PIR2601

PIR3202

PIU407

PIC3601

PIR3402 PIR3501

PIU702

PIC3702

PIR2902

PIU604


PIC4101

PIR4102 PIR4201

PIU506

PIC4102

PIR3801

PIR4202

PIU507

PIC4302

PIC4402

PIU901

PIC4401 PIR4401

PIC4502

PIR4702 PIR4801

PIU802

PIC4602

PIR4502

PIU904


PID401


PID802 PID501


PID902


PIR2302


PIR2402

PID1001 PIR5102


PIJ102

PIJ103

PIJ104

PIQ102

PIR1402

PIR5001 PIQ202

PIR1501

PIR4901



PIDIR101 PIQ302

PIR3301 PIU1201

NLON0OFF1

PIDIR201 PIQ402

PIR4301

PIU1207 NLON0OFF2

PIC1901 PIC2002 PIC2102

PID101

PID801

PIR1002 PIR1102


PIV102 NLV10

PIC2201 PIC2302 PIC2402

PID201

PID901

PIR1202 PIR1302

PITransformer01

PIV201 NLV20

PIC102 PIC202


PIC1801

PIC1902 PIC2001 PIC2101 PIC2202

PIC2301 PIC2401

PIC2701 PIC2801 PIC2901

PIC3001 PIC3201

PIC3701

PIC3802

PIC3901 PIC4001

PIC4601 PIC4702


PID1101

PID6901


PIJ10S

PIR1601 PIR1701 PIR2001 PIR2101

PIR2301 PIR2401

PIR3101

PIR3502

PIR3902

PIR4101

PIR4802

PIR4902 PIR5002

PIR5202 PIR5402


PIU304

PIU404

PIU504 PIU605

PIU704

PIU804

PIU905

PIU1204

PIV101

PIV202

NLV10

NLV20


PIU401

PIU402

NLVout1


PIU501

PIU502

NLVout2

PIQ301

PIR2901 PIU608

NLVref1

PIQ401

PIR4501 PIU908

NLVref2

PIC4301

PIR1001

PIR1602

PIR4402

PIR4602

PIU902

NLVsense101 PIR1101

PIR1702

PIR2502

NLVsense102 PIC3101

PIR1201

PIR2002

PIR2802

PIR3002

PIU602

NLVsense201

PIR1301

PIR2102

PIR3702

NLVsense202


PIR3001

PIR4601

PIVsetp01 NLVsetp


PIR5201

PIU303

NLVsetpPWM

Figure 2-13: Measurement bridge op-amp circuit implementation

The current measurements are done with the same analog signals that are passed to the currentmode control circuit, namely Imeas1 and Imeas2. These can be re-purposed for this use becausethe IC does not force the signal to any value as it does with the voltage sense signals. In orderto not disturb the current sense signal, the signal is fed directly into the op-amp without anyadditional passive filtering. The filtering is done by an active LPF, implemented through C34and C41, and by a passive LPF directly after the op-amp with R26/C32 and R38/C40. Thesefilters are needed because the current sense signal has the shape of a saw-tooth, while the rmsvalue is the only relevant piece of information. The resistors R31/R32 and R41/R42 provide anon-inverting feedback network that sets a gain for the op-amp, scaling the current sense signalto a value between 0V and 3.3V, which is the input range of the microcontroller’s ADC.


2.4 Subsystems 20

2.4.3 Digital to Analog Converter

The Digital to Analog converters (DACs) on the PCB have as function to convert a PWMsignal from the microcontroller into a steady DC signal. The reason behind this is that notall microcontrollers have analog output capabilities, while most do have PWM outputs. Thecircuit represents a comparator that compares the PWM signal to 1.56V. The comparator is fedwith 5V, thus producing the same PWM signal at the output, but switching between 0V and5V instead of the normal 3.3V that most microcontrollers use. The PWM is passed through aLPF that smooths the PWM signal to a steady voltage between 0V and 5V, depending on theduty cycle of the signal.

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

D D

C C

B B

A A

Title



6.8K

R29

2.2nFC37

R28

C31

C33

Q3

12V

R35R34

C365V

0.01ΩR23

1k

R18

1nFC28

Imeas1

Imeas1

R48R47

C455V

0.01ΩR24

1k

R19

1nFC27

Imeas2

Imeas2

300kR11

30kR17

300kR13

30kR21

300kR10

30kR16

300kR12

30kR20

47pFC21

47pFC20

47pFC24

47pFC23Vsense1.1

Vsense2.1

Vsense2.1820uFC22

R44

C43

C44

6.8K

R45

2.2nFC46

Q4Vsense1.1

12V

R27ILim

R40ILim

20k

R46Vsetp

20k

R30Vsetp

GateOut1

GateOut2

Vsense1.2Vsense2.2

100kR33

100kR43

5V

6.7uF C38

6.7uF C47

1KR39 2.2K

R36DIR

ON/OFF2

ON/OFF1

ON/OFF2

ON/OFF1

Vref1

Vref2

Vref2

Vref1

10KR25

Vsense1.2100nF

C30

5V

5V

10KR37

Vsense2.2100nF

C39

Vout1

Vout2

V1+

V1-

V2+

V2-


VsetpPWM

ILimPWM

5V

5V

1K

R8

1K

R22

330nFC29

330nFC18

Vsetp

ILim

DAC's

Isense2

Isense1

5V

5V

Imeas1

Imeas2

R42

C41R41

R32C34

R31

10K

R26

10K

R38

100nFC32

100nFC40

Iout1

Iout2

Measurement Bridge


10Ω

R14

10Ω

R15GateOut1

GateOut2

V1


Transformer

V1+

V2+L1 12V

C5C4C3 C8

Power Distribution

3

21

84 U4A

MCP602-I/P

3

21

84 U5A

MCP602-I/P

75

6

84 U4B

MCP602-I/P

75

6

84 U5B

MCP602-I/P

3

21

84

U7A

3

21

84

U8A

330uFC2

C7

12

V1

12

V2

V1+V1-

V2-V2+

820uFC19

1 23 45 67 89 1011 1213 14

Control Signals

Header 7X2


Connectors

C48 C49 C50

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U6

UC2845N

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U9

UC2845N

31

84

2 1 U12ALM393P

6

572

84

U12BLM393P

5V

5V

31

84

2 1U3ALM393P

6

572

84

U3BLM393P

1V56

1V56

1V56

2.7k R9

2.7kR7

5V

D69

12V

V1 V2

Gate1 Gate2

GND1 GND6

DIR1

DIR2

Vsetp

ILim

1MR49

1MR50

5V

GND2 GND3 GND4GND5

D10LED1

R51

GateOut1 GateOut2

5V

V1-Shield S

VCC 1D- 2

D+ 3GND 4

J1

USB B

R52R53

R54

VsetpPWMILimPWM

DIR

5V

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U2 LM2575HVT-12

100uFC10

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U1 LM2575HVT-5

100uFC1

330uFC9

L2 PI5V01 CO5V

PI12V01 CO12V

PIC101


COC2 PIC301

PIC302 COC3 PIC401

PIC402 COC4 PIC501

PIC502 COC5


PIC802 COC8

PIC901 PIC902

COC9 PIC1001

PIC1002 COC10

PIC1801

PIC1802 COC18

PIC1901

PIC1902

COC19

PIC2001

PIC2002 COC20

PIC2101


PIC2202

COC22 PIC2301

PIC2302 COC23

PIC2401

PIC2402 COC24

PIC2701

PIC2702 COC27

PIC2801

PIC2802 COC28

PIC2901

PIC2902 COC29

PIC3001


COC31

PIC3201

PIC3202 COC32

PIC3301 PIC3302

COC33


PIC3601 PIC3602

COC36

PIC3701

PIC3702 COC37

PIC3801

PIC3802 COC38

PIC3901

PIC3902 COC39

PIC4001

PIC4002 COC40


PIC4301 PIC4302

COC43

PIC4401 PIC4402

COC44

PIC4501 PIC4502

COC45

PIC4601

PIC4602 COC46

PIC4701 PIC4702

COC47

PIC4801



PIC5002 COC50








COControl Signals

PID101 PID102

COD1

PID201 PID202

COD2

PID301 PID302

COD3

PID401 PID402

COD4

PID501 PID502

COD5

PID601 PID602

COD6

PID701 PID702

COD7

PID801 PID802

COD8 PID901 PID902

COD9

PID1001 PID1002


COD11

PID6901 PID6902

COD69

PIDIR101 CODIR1

PIDIR201 CODIR2

PIGate101 COGate1

PIGate201 COGate2

PIGND101 COGND1

PIGND201 COGND2

PIGND301 COGND3

PIGND401 COGND4

PIGND501 COGND5

PIGND601 COGND6

PIILim01 COILim

PIInput01

COInput

PIJ101

PIJ102

PIJ103

PIJ104

PIJ10S

COJ1

PIL101 PIL102

COL1 PIL201 PIL202

COL2

PIQ101 PIQ102

PIQ103 COQ1

PIQ201 PIQ202

PIQ203 COQ2

PIQ301 PIQ302

PIQ303

COQ3

PIQ401 PIQ402

PIQ403

COQ4

PIR701

PIR702

COR7

PIR801 PIR802

COR8

PIR901

PIR902

COR9

PIR1001

PIR1002 COR10

PIR1101

PIR1102 COR11

PIR1201

PIR1202 COR12

PIR1301

PIR1302 COR13

PIR1401 PIR1402


COR15

PIR1601

PIR1602 COR16

PIR1701

PIR1702 COR17

PIR1801 PIR1802


COR19 PIR2001

PIR2002 COR20

PIR2101

PIR2102 COR21

PIR2201 PIR2202

COR22

PIR2301

PIR2302 COR23

PIR2401

PIR2402 COR24

PIR2501 PIR2502

COR25



PIR2801 PIR2802


COR29

PIR3001 PIR3002


PIR3201 PIR3202

COR32

PIR3301

PIR3302

COR33

PIR3401 PIR3402


COR35

PIR3601 PIR3602

COR36

PIR3701 PIR3702

COR37


PIR3901

PIR3902

COR39

PIR4001 PIR4002

COR40


PIR4201 PIR4202

COR42

PIR4301

PIR4302 COR43

PIR4401 PIR4402


COR45




PIR4901

PIR4902

COR49 PIR5001

PIR5002

COR50

PIR5101

PIR5102 COR51

PIR5201

PIR5202

COR52 PIR5301

PIR5302

COR53 PIR5401

PIR5402

COR54

PITransformer00

PITransformer01

PITransformer02


PIU101 PIU102

PIU103

PIU104

PIU105

COU1

PIU201 PIU202

PIU203

PIU204

PIU205

COU2

PIU301

PIU302

PIU303

PIU304

PIU308

COU3A

PIU304

PIU305

PIU306

PIU307

PIU308

COU3B

PIU401

PIU402

PIU403

PIU404

PIU408

COU4A

PIU404 PIU405

PIU406

PIU407

PIU408

COU4B

PIU501

PIU502

PIU503

PIU504

PIU508

COU5A

PIU504 PIU505

PIU506

PIU507

PIU508

COU5B

PIU601

PIU602 PIU603

PIU604

PIU605

PIU606

PIU607

PIU608

COU6

PIU701

PIU702

PIU703

PIU704

PIU708 COU7A

PIU801

PIU802

PIU803

PIU804

PIU808 COU8A

PIU901

PIU902 PIU903

PIU904

PIU905

PIU906

PIU907

PIU908

COU9

PIU1201

PIU1202

PIU1203

PIU1204

PIU1208

COU12A

PIU1204

PIU1205

PIU1206

PIU1207

PIU1208

COU12B

PIV101 COV1

PIV101

PIV102

PIV201 COV2

PIV201

PIV202

PIVsetp01 COVsetp

PIR3602 PIR3901

PIU302

PIU306

PIU1202

PIU1205

NL1V56

PI5V01


PIJ101

PIL202

PIR701

PIR901

PIR3302 PIR3601

PIR4302

PIR5101

PIR5302

PIU104

PIU308

PIU408

PIU508

PIU708

PIU808

PIU1208

NL5V

PI12V01 PIC201

PIC3801

PIC4701

PIL102

PIU204

PIU607

PIU907


PIR5401

PIU1203

PIU1206

NLDIR

PIGate101

PIR1401

PIU606


PIR1502

PIU906

NLGateOut2

PIC2902

PIILim01 PIR2201

PIR2702

PIR4002

NLILim


PIR5301

PIU305

NLILimPWM

PIC2802 PIR1802

PIR2701

PIU405

PIU703

NLImeas1

PIC2702 PIR1901

PIR4001

PIU505

PIU803

NLImeas2

PIC3202


PIR2602 NLIout1

PIC4002


PIR3802 NLIout2

PIC3602

PIQ303

PIR3401

PIU603 PIU701

NLIsense1

PIC4501

PIQ403

PIR4701

PIU801 PIU903

NLIsense2

PIC101 PIC1001

PID102

PID202

PIInput01

PIU101

PIU201


PIC3102

PIC3302

PIU601

PIC3301 PIR2801

PIC3401

PIR3102 PIR3201

PIU406

PIC3402

PIR2601

PIR3202

PIU407

PIC3601

PIR3402 PIR3501

PIU702

PIC3702

PIR2902

PIU604


PIC4101

PIR4102 PIR4201

PIU506

PIC4102

PIR3801

PIR4202

PIU507

PIC4302

PIC4402

PIU901

PIC4401 PIR4401

PIC4502

PIR4702 PIR4801

PIU802

PIC4602

PIR4502

PIU904


PID401


PID802 PID501


PID902


PIR2302


PIR2402

PID1001 PIR5102


PIJ102

PIJ103

PIJ104

PIQ102

PIR1402

PIR5001 PIQ202

PIR1501

PIR4901



PIDIR101 PIQ302

PIR3301 PIU1201

NLON0OFF1

PIDIR201 PIQ402

PIR4301

PIU1207 NLON0OFF2

PIC1901 PIC2002 PIC2102

PID101

PID801

PIR1002 PIR1102


PIV102 NLV10

PIC2201 PIC2302 PIC2402

PID201

PID901

PIR1202 PIR1302

PITransformer01

PIV201 NLV20

PIC102 PIC202


PIC1801

PIC1902 PIC2001 PIC2101 PIC2202

PIC2301 PIC2401

PIC2701 PIC2801 PIC2901

PIC3001 PIC3201

PIC3701

PIC3802

PIC3901 PIC4001

PIC4601 PIC4702


PID1101

PID6901


PIJ10S

PIR1601 PIR1701 PIR2001 PIR2101

PIR2301 PIR2401

PIR3101

PIR3502

PIR3902

PIR4101

PIR4802

PIR4902 PIR5002

PIR5202 PIR5402


PIU304

PIU404

PIU504 PIU605

PIU704

PIU804

PIU905

PIU1204

PIV101

PIV202

NLV10

NLV20


PIU401

PIU402

NLVout1


PIU501

PIU502

NLVout2

PIQ301

PIR2901 PIU608

NLVref1

PIQ401

PIR4501 PIU908

NLVref2

PIC4301

PIR1001

PIR1602

PIR4402

PIR4602

PIU902

NLVsense101 PIR1101

PIR1702

PIR2502

NLVsense102 PIC3101

PIR1201

PIR2002

PIR2802

PIR3002

PIU602

NLVsense201

PIR1301

PIR2102

PIR3702

NLVsense202


PIR3001

PIR4601

PIVsetp01 NLVsetp


PIR5201

PIU303

NLVsetpPWM

Figure 2-14: Digital to Analog circuit implementation

This implementation allows the converter to be controlled by almost any PWM signal which ispresent on nearly all microcontrollers, and the generation of the DC signal is independent ofthe voltage of the PWM signal, as long as its digital high is above 1.56V. The zener diode D69has been added to add the feature to limit Vsetp, and thus Vout, in hardware on the converteritself, adding another level of safety.


2.4 Subsystems 21

2.4.4 Direction Comparator

The direction comparator section of the converter takes a digital signal from the microcontroller(0V or 3V) and converts it into two inverted signals (0V or 5V) used to control the transistorsQ3 and Q4 in the current mode control circuit, described in subsection 2.4.1. This way themicrocontroller can determine the energy flow direction of the converter by the use of a singledigital output signal.

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

D D

C C

B B

A A

Title



6.8K

R29

2.2nFC37

R28

C31

C33

Q3

12V

R35R34

C365V

0.01ΩR23

1k

R18

1nFC28

Imeas1

Imeas1

R48R47

C455V

0.01ΩR24

1k

R19

1nFC27

Imeas2

Imeas2

300kR11

30kR17

300kR13

30kR21

300kR10

30kR16

300kR12

30kR20

47pFC21

47pFC20

47pFC24

47pFC23Vsense1.1

Vsense2.1

Vsense2.1820uFC22

R44

C43

C44

6.8K

R45

2.2nFC46

Q4Vsense1.1

12V

R27ILim

R40ILim

20k

R46Vsetp

20k

R30Vsetp

GateOut1

GateOut2

Vsense1.2Vsense2.2

100kR33

100kR43

5V

6.7uF C38

6.7uF C47

1KR39 2.2K

R36DIR

ON/OFF2

ON/OFF1

ON/OFF2

ON/OFF1

Vref1

Vref2

Vref2

Vref1

10KR25

Vsense1.2100nF

C30

5V

5V

10KR37

Vsense2.2100nF

C39

Vout1

Vout2

V1+

V1-

V2+

V2-


VsetpPWM

ILimPWM

5V

5V

1K

R8

1K

R22

330nFC29

330nFC18

Vsetp

ILim

DAC's

Isense2

Isense1

5V

5V

Imeas1

Imeas2

R42

C41R41

R32C34

R31

10K

R26

10K

R38

100nFC32

100nFC40

Iout1

Iout2

Measurement Bridge


10Ω

R14

10Ω

R15GateOut1

GateOut2

V1


Transformer

V1+

V2+L1 12V

C5C4C3 C8

Power Distribution

3

21

84 U4A

MCP602-I/P

3

21

84 U5A

MCP602-I/P

75

6

84 U4B

MCP602-I/P

75

6

84 U5B

MCP602-I/P

3

21

84

U7A

3

21

84

U8A

330uFC2

C7

12

V1

12

V2

V1+V1-

V2-V2+

820uFC19

1 23 45 67 89 1011 1213 14

Control Signals

Header 7X2


Connectors

C48 C49 C50

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U6

UC2845N

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U9

UC2845N

31

84

2 1 U12ALM393P

6

572

84

U12BLM393P

5V

5V

31

84

2 1U3ALM393P

6

572

84

U3BLM393P

1V56

1V56

1V56

2.7k R9

2.7kR7

5V

D69

12V

V1 V2

Gate1 Gate2

GND1 GND6

DIR1

DIR2

Vsetp

ILim

1MR49

1MR50

5V

GND2 GND3 GND4GND5

D10LED1

R51

GateOut1 GateOut2

5V

V1-Shield S

VCC 1D- 2

D+ 3GND 4

J1

USB B

R52R53

R54

VsetpPWMILimPWM

DIR

5V

Input1G

ND

3

ON

/OFF

5Output 2

Feedback 4

U2 LM2575HVT-12

100uFC10

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U1 LM2575HVT-5

100uFC1

330uFC9

L2 PI5V01 CO5V

PI12V01 CO12V

PIC101


COC2 PIC301

PIC302 COC3 PIC401

PIC402 COC4 PIC501

PIC502 COC5


PIC802 COC8

PIC901 PIC902

COC9 PIC1001

PIC1002 COC10

PIC1801

PIC1802 COC18

PIC1901

PIC1902

COC19

PIC2001

PIC2002 COC20

PIC2101


PIC2202

COC22 PIC2301

PIC2302 COC23

PIC2401

PIC2402 COC24

PIC2701

PIC2702 COC27

PIC2801

PIC2802 COC28

PIC2901

PIC2902 COC29

PIC3001


COC31

PIC3201

PIC3202 COC32

PIC3301 PIC3302

COC33


PIC3601 PIC3602

COC36

PIC3701

PIC3702 COC37

PIC3801

PIC3802 COC38

PIC3901

PIC3902 COC39

PIC4001

PIC4002 COC40


PIC4301 PIC4302

COC43

PIC4401 PIC4402

COC44

PIC4501 PIC4502

COC45

PIC4601

PIC4602 COC46

PIC4701 PIC4702

COC47

PIC4801



PIC5002 COC50








COControl Signals

PID101 PID102

COD1

PID201 PID202

COD2

PID301 PID302

COD3

PID401 PID402

COD4

PID501 PID502

COD5

PID601 PID602

COD6

PID701 PID702

COD7

PID801 PID802

COD8 PID901 PID902

COD9

PID1001 PID1002


COD11

PID6901 PID6902

COD69

PIDIR101 CODIR1

PIDIR201 CODIR2

PIGate101 COGate1

PIGate201 COGate2

PIGND101 COGND1

PIGND201 COGND2

PIGND301 COGND3

PIGND401 COGND4

PIGND501 COGND5

PIGND601 COGND6

PIILim01 COILim

PIInput01

COInput

PIJ101

PIJ102

PIJ103

PIJ104

PIJ10S

COJ1

PIL101 PIL102

COL1 PIL201 PIL202

COL2

PIQ101 PIQ102

PIQ103 COQ1

PIQ201 PIQ202

PIQ203 COQ2

PIQ301 PIQ302

PIQ303

COQ3

PIQ401 PIQ402

PIQ403

COQ4

PIR701

PIR702

COR7

PIR801 PIR802

COR8

PIR901

PIR902

COR9

PIR1001

PIR1002 COR10

PIR1101

PIR1102 COR11

PIR1201

PIR1202 COR12

PIR1301

PIR1302 COR13

PIR1401 PIR1402


COR15

PIR1601

PIR1602 COR16

PIR1701

PIR1702 COR17

PIR1801 PIR1802


COR19 PIR2001

PIR2002 COR20

PIR2101

PIR2102 COR21

PIR2201 PIR2202

COR22

PIR2301

PIR2302 COR23

PIR2401

PIR2402 COR24

PIR2501 PIR2502

COR25



PIR2801 PIR2802


COR29

PIR3001 PIR3002


PIR3201 PIR3202

COR32

PIR3301

PIR3302

COR33

PIR3401 PIR3402


COR35

PIR3601 PIR3602

COR36

PIR3701 PIR3702

COR37


PIR3901

PIR3902

COR39

PIR4001 PIR4002

COR40


PIR4201 PIR4202

COR42

PIR4301

PIR4302 COR43

PIR4401 PIR4402


COR45




PIR4901

PIR4902

COR49 PIR5001

PIR5002

COR50

PIR5101

PIR5102 COR51

PIR5201

PIR5202

COR52 PIR5301

PIR5302

COR53 PIR5401

PIR5402

COR54

PITransformer00

PITransformer01

PITransformer02


PIU101 PIU102

PIU103

PIU104

PIU105

COU1

PIU201 PIU202

PIU203

PIU204

PIU205

COU2

PIU301

PIU302

PIU303

PIU304

PIU308

COU3A

PIU304

PIU305

PIU306

PIU307

PIU308

COU3B

PIU401

PIU402

PIU403

PIU404

PIU408

COU4A

PIU404 PIU405

PIU406

PIU407

PIU408

COU4B

PIU501

PIU502

PIU503

PIU504

PIU508

COU5A

PIU504 PIU505

PIU506

PIU507

PIU508

COU5B

PIU601

PIU602 PIU603

PIU604

PIU605

PIU606

PIU607

PIU608

COU6

PIU701

PIU702

PIU703

PIU704

PIU708 COU7A

PIU801

PIU802

PIU803

PIU804

PIU808 COU8A

PIU901

PIU902 PIU903

PIU904

PIU905

PIU906

PIU907

PIU908

COU9

PIU1201

PIU1202

PIU1203

PIU1204

PIU1208

COU12A

PIU1204

PIU1205

PIU1206

PIU1207

PIU1208

COU12B

PIV101 COV1

PIV101

PIV102

PIV201 COV2

PIV201

PIV202

PIVsetp01 COVsetp

PIR3602 PIR3901

PIU302

PIU306

PIU1202

PIU1205

NL1V56

PI5V01


PIJ101

PIL202

PIR701

PIR901

PIR3302 PIR3601

PIR4302

PIR5101

PIR5302

PIU104

PIU308

PIU408

PIU508

PIU708

PIU808

PIU1208

NL5V

PI12V01 PIC201

PIC3801

PIC4701

PIL102

PIU204

PIU607

PIU907


PIR5401

PIU1203

PIU1206

NLDIR

PIGate101

PIR1401

PIU606


PIR1502

PIU906

NLGateOut2

PIC2902

PIILim01 PIR2201

PIR2702

PIR4002

NLILim


PIR5301

PIU305

NLILimPWM

PIC2802 PIR1802

PIR2701

PIU405

PIU703

NLImeas1

PIC2702 PIR1901

PIR4001

PIU505

PIU803

NLImeas2

PIC3202


PIR2602 NLIout1

PIC4002


PIR3802 NLIout2

PIC3602

PIQ303

PIR3401

PIU603 PIU701

NLIsense1

PIC4501

PIQ403

PIR4701

PIU801 PIU903

NLIsense2

PIC101 PIC1001

PID102

PID202

PIInput01

PIU101

PIU201


PIC3102

PIC3302

PIU601

PIC3301 PIR2801

PIC3401

PIR3102 PIR3201

PIU406

PIC3402

PIR2601

PIR3202

PIU407

PIC3601

PIR3402 PIR3501

PIU702

PIC3702

PIR2902

PIU604


PIC4101

PIR4102 PIR4201

PIU506

PIC4102

PIR3801

PIR4202

PIU507

PIC4302

PIC4402

PIU901

PIC4401 PIR4401

PIC4502

PIR4702 PIR4801

PIU802

PIC4602

PIR4502

PIU904


PID401


PID802 PID501


PID902


PIR2302


PIR2402

PID1001 PIR5102


PIJ102

PIJ103

PIJ104

PIQ102

PIR1402

PIR5001 PIQ202

PIR1501

PIR4901



PIDIR101 PIQ302

PIR3301 PIU1201

NLON0OFF1

PIDIR201 PIQ402

PIR4301

PIU1207 NLON0OFF2

PIC1901 PIC2002 PIC2102

PID101

PID801

PIR1002 PIR1102


PIV102 NLV10

PIC2201 PIC2302 PIC2402

PID201

PID901

PIR1202 PIR1302

PITransformer01

PIV201 NLV20

PIC102 PIC202


PIC1801

PIC1902 PIC2001 PIC2101 PIC2202

PIC2301 PIC2401

PIC2701 PIC2801 PIC2901

PIC3001 PIC3201

PIC3701

PIC3802

PIC3901 PIC4001

PIC4601 PIC4702


PID1101

PID6901


PIJ10S

PIR1601 PIR1701 PIR2001 PIR2101

PIR2301 PIR2401

PIR3101

PIR3502

PIR3902

PIR4101

PIR4802

PIR4902 PIR5002

PIR5202 PIR5402


PIU304

PIU404

PIU504 PIU605

PIU704

PIU804

PIU905

PIU1204

PIV101

PIV202

NLV10

NLV20


PIU401

PIU402

NLVout1


PIU501

PIU502

NLVout2

PIQ301

PIR2901 PIU608

NLVref1

PIQ401

PIR4501 PIU908

NLVref2

PIC4301

PIR1001

PIR1602

PIR4402

PIR4602

PIU902

NLVsense101 PIR1101

PIR1702

PIR2502

NLVsense102 PIC3101

PIR1201

PIR2002

PIR2802

PIR3002

PIU602

NLVsense201

PIR1301

PIR2102

PIR3702

NLVsense202


PIR3001

PIR4601

PIVsetp01 NLVsetp


PIR5201

PIU303

NLVsetpPWM

Figure 2-15: Direction signal comparator implementation

The 1.56V compare voltage is generated using a resistor divider network of 2.2K and 1K,implemented through R36 and R39. The digital signal is fed into a different input of eithercomparator, ensuring that the output signals ON/OFF1 and ON/OFF2 are inverted. R33and R43 function as pull-up resistors for the comparator as these do not have any internalpull-ups.


2.4 Subsystems 22

2.4.5 Power Supply

The voltages needed for the converter subsystems are 12V and 5V. Both of these are generatedby the power distribution section of the converter. The LM2575HVT IC family is used as theyhave a large input voltage range and an easy direct feedback network, which makes it easy toimplement. Specific models used are the LM2575HVT-12 and LM2575HVT-5, corresponding tothe 12V and 5V direct feedback variant of the general IC family. The IC’s inputs are connectedthrough diodes to both sides of the converters high-power path. This results in the powerdistribution being fed from whichever of the sides has the highest voltage, negating the needfor a separate power input. The large input range of the IC’s also ensures that the convertercan be powered throughout the whole input and output range specifications of 12V to 48V.

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

D D

C C

B B

A A

Title



6.8K

R29

2.2nFC37

R28

C31

C33

Q3

12V

R35R34

C365V

0.01ΩR23

1k

R18

1nFC28

Imeas1

Imeas1

R48R47

C455V

0.01ΩR24

1k

R19

1nFC27

Imeas2

Imeas2

300kR11

30kR17

300kR13

30kR21

300kR10

30kR16

300kR12

30kR20

47pFC21

47pFC20

47pFC24

47pFC23Vsense1.1

Vsense2.1

Vsense2.1820uFC22

R44

C43

C44

6.8K

R45

2.2nFC46

Q4Vsense1.1

12V

R27ILim

R40ILim

20k

R46Vsetp

20k

R30Vsetp

GateOut1

GateOut2

Vsense1.2Vsense2.2

100kR33

100kR43

5V

6.7uF C38

6.7uF C47

1KR39 2.2K

R36DIR

ON/OFF2

ON/OFF1

ON/OFF2

ON/OFF1

Vref1

Vref2

Vref2

Vref1

10KR25

Vsense1.2100nF

C30

5V

5V

10KR37

Vsense2.2100nF

C39

Vout1

Vout2

V1+

V1-

V2+

V2-


VsetpPWM

ILimPWM

5V

5V

1K

R8

1K

R22

330nFC29

330nFC18

Vsetp

ILim

DAC's

Isense2

Isense1

5V

5V

Imeas1

Imeas2

R42

C41R41

R32C34

R31

10K

R26

10K

R38

100nFC32

100nFC40

Iout1

Iout2

Measurement Bridge


10Ω

R14

10Ω

R15GateOut1

GateOut2

V1


Transformer

V1+

V2+L1 12V

C5C4C3 C8

Power Distribution

3

21

84 U4A

MCP602-I/P

3

21

84 U5A

MCP602-I/P

75

6

84 U4B

MCP602-I/P

75

6

84 U5B

MCP602-I/P

3

21

84

U7A

3

21

84

U8A

330uFC2

C7

12

V1

12

V2

V1+V1-

V2-V2+

820uFC19

1 23 45 67 89 1011 1213 14

Control Signals

Header 7X2


Connectors

C48 C49 C50

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U6

UC2845N

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U9

UC2845N

31

84

2 1 U12ALM393P

6

572

84

U12BLM393P

5V

5V

31

84

2 1U3ALM393P

6

572

84

U3BLM393P

1V56

1V56

1V56

2.7k R9

2.7kR7

5V

D69

12V

V1 V2

Gate1 Gate2

GND1 GND6

DIR1

DIR2

Vsetp

ILim

1MR49

1MR50

5V

GND2 GND3 GND4GND5

D10LED1

R51

GateOut1 GateOut2

5V

V1-Shield S

VCC 1D- 2

D+ 3GND 4

J1

USB B

R52R53

R54

VsetpPWMILimPWM

DIR

5V

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U2 LM2575HVT-12

100uFC10

Input1G

ND

3

ON

/OFF

5

Output 2

Feedback 4

U1 LM2575HVT-5

100uFC1

330uFC9

L2 PI5V01 CO5V

PI12V01 CO12V

PIC101


COC2 PIC301

PIC302 COC3 PIC401

PIC402 COC4 PIC501

PIC502 COC5


PIC802 COC8

PIC901 PIC902

COC9 PIC1001

PIC1002 COC10

PIC1801

PIC1802 COC18

PIC1901

PIC1902

COC19

PIC2001

PIC2002 COC20

PIC2101


PIC2202

COC22 PIC2301

PIC2302 COC23

PIC2401

PIC2402 COC24

PIC2701

PIC2702 COC27

PIC2801

PIC2802 COC28

PIC2901

PIC2902 COC29

PIC3001


COC31

PIC3201

PIC3202 COC32

PIC3301 PIC3302

COC33


PIC3601 PIC3602

COC36

PIC3701

PIC3702 COC37

PIC3801

PIC3802 COC38

PIC3901

PIC3902 COC39

PIC4001

PIC4002 COC40


PIC4301 PIC4302

COC43

PIC4401 PIC4402

COC44

PIC4501 PIC4502

COC45

PIC4601

PIC4602 COC46

PIC4701 PIC4702

COC47

PIC4801



PIC5002 COC50








COControl Signals

PID101 PID102

COD1

PID201 PID202

COD2

PID301 PID302

COD3

PID401 PID402

COD4

PID501 PID502

COD5

PID601 PID602

COD6

PID701 PID702

COD7

PID801 PID802

COD8 PID901 PID902

COD9

PID1001 PID1002


COD11

PID6901 PID6902

COD69

PIDIR101 CODIR1

PIDIR201 CODIR2

PIGate101 COGate1

PIGate201 COGate2

PIGND101 COGND1

PIGND201 COGND2

PIGND301 COGND3

PIGND401 COGND4

PIGND501 COGND5

PIGND601 COGND6

PIILim01 COILim

PIInput01

COInput

PIJ101

PIJ102

PIJ103

PIJ104

PIJ10S

COJ1

PIL101 PIL102

COL1 PIL201 PIL202

COL2

PIQ101 PIQ102

PIQ103 COQ1

PIQ201 PIQ202

PIQ203 COQ2

PIQ301 PIQ302

PIQ303

COQ3

PIQ401 PIQ402

PIQ403

COQ4

PIR701

PIR702

COR7

PIR801 PIR802

COR8

PIR901

PIR902

COR9

PIR1001

PIR1002 COR10

PIR1101

PIR1102 COR11

PIR1201

PIR1202 COR12

PIR1301

PIR1302 COR13

PIR1401 PIR1402


COR15

PIR1601

PIR1602 COR16

PIR1701

PIR1702 COR17

PIR1801 PIR1802


COR19 PIR2001

PIR2002 COR20

PIR2101

PIR2102 COR21

PIR2201 PIR2202

COR22

PIR2301

PIR2302 COR23

PIR2401

PIR2402 COR24

PIR2501 PIR2502

COR25



PIR2801 PIR2802


COR29

PIR3001 PIR3002


PIR3201 PIR3202

COR32

PIR3301

PIR3302

COR33

PIR3401 PIR3402


COR35

PIR3601 PIR3602

COR36

PIR3701 PIR3702

COR37


PIR3901

PIR3902

COR39

PIR4001 PIR4002

COR40


PIR4201 PIR4202

COR42

PIR4301

PIR4302 COR43

PIR4401 PIR4402


COR45




PIR4901

PIR4902

COR49 PIR5001

PIR5002

COR50

PIR5101

PIR5102 COR51

PIR5201

PIR5202

COR52 PIR5301

PIR5302

COR53 PIR5401

PIR5402

COR54

PITransformer00

PITransformer01

PITransformer02


PIU101 PIU102

PIU103

PIU104

PIU105

COU1

PIU201 PIU202

PIU203

PIU204

PIU205

COU2

PIU301

PIU302

PIU303

PIU304

PIU308

COU3A

PIU304

PIU305

PIU306

PIU307

PIU308

COU3B

PIU401

PIU402

PIU403

PIU404

PIU408

COU4A

PIU404 PIU405

PIU406

PIU407

PIU408

COU4B

PIU501

PIU502

PIU503

PIU504

PIU508

COU5A

PIU504 PIU505

PIU506

PIU507

PIU508

COU5B

PIU601

PIU602 PIU603

PIU604

PIU605

PIU606

PIU607

PIU608

COU6

PIU701

PIU702

PIU703

PIU704

PIU708 COU7A

PIU801

PIU802

PIU803

PIU804

PIU808 COU8A

PIU901

PIU902 PIU903

PIU904

PIU905

PIU906

PIU907

PIU908

COU9

PIU1201

PIU1202

PIU1203

PIU1204

PIU1208

COU12A

PIU1204

PIU1205

PIU1206

PIU1207

PIU1208

COU12B

PIV101 COV1

PIV101

PIV102

PIV201 COV2

PIV201

PIV202

PIVsetp01 COVsetp

PIR3602 PIR3901

PIU302

PIU306

PIU1202

PIU1205

NL1V56

PI5V01


PIJ101

PIL202

PIR701

PIR901

PIR3302 PIR3601

PIR4302

PIR5101

PIR5302

PIU104

PIU308

PIU408

PIU508

PIU708

PIU808

PIU1208

NL5V

PI12V01 PIC201

PIC3801

PIC4701

PIL102

PIU204

PIU607

PIU907


PIR5401

PIU1203

PIU1206

NLDIR

PIGate101

PIR1401

PIU606


PIR1502

PIU906

NLGateOut2

PIC2902

PIILim01 PIR2201

PIR2702

PIR4002

NLILim


PIR5301

PIU305

NLILimPWM

PIC2802 PIR1802

PIR2701

PIU405

PIU703

NLImeas1

PIC2702 PIR1901

PIR4001

PIU505

PIU803

NLImeas2

PIC3202


PIR2602 NLIout1

PIC4002


PIR3802 NLIout2

PIC3602

PIQ303

PIR3401

PIU603 PIU701

NLIsense1

PIC4501

PIQ403

PIR4701

PIU801 PIU903

NLIsense2

PIC101 PIC1001

PID102

PID202

PIInput01

PIU101

PIU201


PIC3102

PIC3302

PIU601

PIC3301 PIR2801

PIC3401

PIR3102 PIR3201

PIU406

PIC3402

PIR2601

PIR3202

PIU407

PIC3601

PIR3402 PIR3501

PIU702

PIC3702

PIR2902

PIU604


PIC4101

PIR4102 PIR4201

PIU506

PIC4102

PIR3801

PIR4202

PIU507

PIC4302

PIC4402

PIU901

PIC4401 PIR4401

PIC4502

PIR4702 PIR4801

PIU802

PIC4602

PIR4502

PIU904


PID401


PID802 PID501


PID902


PIR2302


PIR2402

PID1001 PIR5102


PIJ102

PIJ103

PIJ104

PIQ102

PIR1402

PIR5001 PIQ202

PIR1501

PIR4901



PIDIR101 PIQ302

PIR3301 PIU1201

NLON0OFF1

PIDIR201 PIQ402

PIR4301

PIU1207 NLON0OFF2

PIC1901 PIC2002 PIC2102

PID101

PID801

PIR1002 PIR1102


PIV102 NLV10

PIC2201 PIC2302 PIC2402

PID201

PID901

PIR1202 PIR1302

PITransformer01

PIV201 NLV20

PIC102 PIC202


PIC1801

PIC1902 PIC2001 PIC2101 PIC2202

PIC2301 PIC2401

PIC2701 PIC2801 PIC2901

PIC3001 PIC3201

PIC3701

PIC3802

PIC3901 PIC4001

PIC4601 PIC4702


PID1101

PID6901


PIJ10S

PIR1601 PIR1701 PIR2001 PIR2101

PIR2301 PIR2401

PIR3101

PIR3502

PIR3902

PIR4101

PIR4802

PIR4902 PIR5002

PIR5202 PIR5402


PIU304

PIU404

PIU504 PIU605

PIU704

PIU804

PIU905

PIU1204

PIV101

PIV202

NLV10

NLV20


PIU401

PIU402

NLVout1


PIU501

PIU502

NLVout2

PIQ301

PIR2901 PIU608

NLVref1

PIQ401

PIR4501 PIU908

NLVref2

PIC4301

PIR1001

PIR1602

PIR4402

PIR4602

PIU902

NLVsense101 PIR1101

PIR1702

PIR2502

NLVsense102 PIC3101

PIR1201

PIR2002

PIR2802

PIR3002

PIU602

NLVsense201

PIR1301

PIR2102

PIR3702

NLVsense202


PIR3001

PIR4601

PIVsetp01 NLVsetp


PIR5201

PIU303

NLVsetpPWM

Figure 2-16: Power supply IC implementation

The IC has a built in switching component, and together with a diode, inductor and capacitoron the output it forms a simple and robust buck-converter [31]. A LED has been added on the5V rail to serve as visual feedback on the power state of the converter. The capacitors on the5V rail serve as bypass capacitors for all the other subsystems working with 5V [33].


2.5 Use 23

2.5 Use

Initially, the flyback converter is designed for the eBike solar charging station located at thecampus of the TU Delft. The charging station next to the EEMCS tower is equipped with 8solar panels, capable of a total peak power of 2.3 kW, see figure 2-17 [19]. The flyback converterwill be a small but important link in this chain, capable of regulating a load voltage and limitingthe output current, while being fed from an input DC voltage varying between 36V and 48V.The regulating and bi-directional aspect is put in place in order to make the converter applicablein other areas as well, for instance DC microgrids.

Figure 2-17: eBike solar charging station

The implemented control and measurementsignals ensure easy operation of the converterwhen integrated into a larger system. Foran example of the control network, the thesis"Control Network of Bi-Directional DC/DCConverters" by BAP group B1 can be con-sulted [35]. The proposed control networkfeatures a slave in the form of the OlimexLPC1343 development board, and the mas-ter as an ODROID C1+. The control net-work design use is best illustrated with theintended functionality of charging eBikes. Auser deposits their eBike at the charging sta-tion and accesses a website used for track-ing and controlling the charging functionali-ties. Any command sent by the user is passedon through server, master and slave, to fi-nally arrive at the the corresponding con-verter. All measurements are readily availableto the user, unbounded of location.


Simulations

3.1 Uni-directional

To illustrate the workings of a flyback converter implementation with the UC2845 IC, a simpler,uni-directional simulation has been provided in figure 3-1. This circuit topology consists of theswitching MOSFET on the primary side of the circuit, and the MOSFET on the secondary sideacting as the flyback diode. The voltage set-point and current limit have been left out to focuson the fundamental operation first. The working of the simulated UC3842 is identical to theUC2845.

High Power

IC measurements

Filtering

Feedback Network

Vfb

Isense

RtCt

Vref

Vcc

Out

Gnd

UC3842

-

+

OA

RLOAD 200

LP 20uH LS 20uH

R5 1k

R6

9k

R3 0.01

R4

1k

C1 820uF

V1 20

+

-

C4 2.2n

C3 0.1uFC2 820uFR2 30k

R1 300k

R31 0.01

K 0.95

R10

7.5kImeas

Imeas

VOUTVIN

Vgate

Vgate

Figure 3-1: Uni-directional flyback converter implementation with UC2845


3.1 Uni-directional 25

Figure 3-2 shows the gate signal, output of the IC, and the Isense signal, input of the IC. TheIC will generate a PWM signal of a certain frequency according to the resistor and capacitorvalues R10/C4. The duty cycle is internally limited to 50% for ease of operation. The internalerror amplifier and PWM comparator determine the duty cycle of the PWM signal through themeasurements of the voltage at Vfb and the shunt resistor (R3 ) voltage at Isense. Figure 3-2evidently shows the gate signal falling to zero when the current measurement at Isense equals1V. A simulation of the block diagram can be seen in appendix A figure A-3.

Figure 3-2: UC2845 MOSFET gate signal regulating.

Figure 3-3 shows the start-up of the converter. The current is not limited, and the voltage set-point has not been attached. The distinction can be made between the start-up and regulatedload scenarios. When the IC does not measure its desired voltage output, it will allow maximumcurrent to flow until the voltage rises enough to fulfill that criteria (0-5ms). When the voltagedemand has been met, the IC will actively keep the voltage level steady while supplying currentto the load (5-10ms). In this operating mode the IC will supply as much current as needed bythe load until it reaches its maximum, which is set by the current limit.

Figure 3-3: Power converter start-up and regulated load electrical characteristics.


3.1 Uni-directional 26

Although the design of the feedback compensation network of the IC isn’t the main objectiveof this thesis, it is still of considerable importance to the functioning of the converter. The taskof the feedback compensation network is to shape the loop gain such that it has a crossoverfrequency at a desired place with enough phase and gain margins for good dynamic response,line and load regulation, and stability [15]. For this bi-directional flyback converter a type-II compensation network is more than sufficient, with an integrator, one pole, and one zero.The values of the compensation network determine the actual transfer function parameters andshould be calculated to achieve the desired cross-over frequency and gain- and phase-margin[16]. Figures 3-4 and 3-5 show the difference between a well-calculated feedback compensationnetwork and a poorly-chosen one.

Figure 3-4: Settling characteristics of regulating IC with poorly-chosen feedback compensationnetwork.

Figure 3-5: Settling characteristics of regulating IC with well-chosen feedback compensation net-work.


3.2 Bi-directional 27

3.2 Bi-directional

Figure 3-6 illustrates the bi-directional implementation of the converter. A second UC2845and corresponding circuitry has been added, as well as a NPN transistor on both Isense lines.The signal DIR is provided to the base of one transistor, while the inverted signal notDIR isprovided to the other transistor. This ensures that only one IC will be active at all times, andthe other will be inactive as Isense is pulled to Vref.

Lastly, the voltage set-point and current limit have been implemented in the form of V5 andV6. The signals are applied to both IC’s, as they are only of influence on the active IC.

Feedback Network

Filtering

IC measurements

High Power

R8 30k

R5 300k

V3

+-V4

+-

C31 0.1uF C1 820uF

LP 20uH

R3 0.01

R4

1k

C3 0.1uFC2 820uFR2 30k

R1 300k

R7 0.01

LS 20uH

K1 0.95

R9

1k

V6

3+-

V5

+-

R10 1k

R11

9kVfb

Isense

RtCt

Vref

Vcc

Out

Gnd

UC3842-

+

OA

R12 1k

R13

9k

-

+

OA

Vfb

Isense

RtCt

Vref

Vcc

Out

Gnd

UC3842

V1 48

+

-RLOAD 200R

RLOAD1 200R V2 12

+

-

V2

notDIR

notDIR

DIR

Vgate1

Vsense2

Vgate2

Vsense1

Imeas2Imeas1

V1

Imeas1

Vsense2

Vsense1

Imeas2

Vref

Imeas1

Vsense1

Vgate1

DIR

Imeas2

Vsense2

Vgate2

Vref

notDIRDIRnotDIRDIR

Figure 3-6: Bi-directional flyback converter implementation with UC2845


3.2 Bi-directional 28

Figure 3-7 is a simulation of the converter switching energy direction. The direction signal isalternated, periodically switching source and load side, as well as the active IC. Evident in thesimulation is the alternating current direction and the corresponding load voltage regulation.

Figure 3-7: Alternating energy direction in bi-directional flyback converter


PCB Design

Printed Circuit Board (PCB) layout is important for switch-mode power supplies since thereare high switching currents and sensitive control signals in the vicinity. A well-designed PCBleads to better performance, lower cost, higher reliability and reduced electromagnetic interfer-ence(EMI). There are a couple of general guidelines that have to be met: the current carryingtraces must be as thick, short and direct as possible, the board must have a low-impedanceground and sensitive signals must be shielded from interference by noisy traces[11].

4.1 Design Layout

There are a few critical current paths in our flyback converter. An overview of the entire layoutcan be found in Appendix A figure A-2. The high power traces and transformer connectionpads are critical to the working of the switching converter. Some of these traces have high di

dt

and dvdt originating from pulsating currents, while others have high RMS continuous current.

These traces will introduce a significant amount of noise if not filtered and handled correctly.The high dv

dt traces and the transformers will also contribute considerably to the generatedEMI. Therefore, these are ideally placed well away from sensitive, analog signals on-board,as well as away from the microcontroller board. An illustration of these paths and the PCBimplementation on our converter can be seen in figure 4-1 and figure 4-2, respectively.Both the pulsating and continuous current traces are placed distant from other sensitive, analogcontrol signals. Furthermore, the traces consist of big copper pads to more effectively managehigher currents by providing a larger thermal mass and less resistance. The ground connectionis done through a ground plane on the bottom layer. Due to this layout, there are four inevitablemeasurement hazards, encircled blue in figure 4-2, where the measurement will pick up extranoise due to the noisy ground plane directly underneath it.

Figure 4-1: Pulsating and continuous current paths in flyback converter


4.1 Design Layout 30

Figure 4-2: Pulsating and continuous current paths in flyback converter PCB

Figure 4-3: MOSFET gate signal currentreturn path

Another critical current path is the MOSFET gate sig-nal path. The IC decides whether to turn on or offthe MOSFET depending on the internal circuitry. Ifthe IC decides to turn the MOSFET on, it will try todo so as fast as possible. If no gate resistance is used,the IC’s output is not current limited and might re-sult in an unstable system. The current peaks up to500mA that the IC draws when opening the gate aredrawn from the bypass capacitor C38, which is thereforeplaced close to the IC’s pins. The current is returned tothe IC through the shunt resistor and the ground plane.Ideally this path is as short and compact as possible toreduce noise picked up by the current loop and increasestability [28].


Evaluation

5.1 Overview

In order to test the design of the flyback converter a testplan was made. The main goal is tocheck whether the requirements stated in section 1.3 are met. However, before the requirementscan be looked at, it is important to populate and test the design’s subsystems independently,before looking at the system performance as a whole.

First of all, the components of the power supply are placed on the PCB. To check whetherthe 5V and 12V line are working properly, the test-points 5V and 12V are used. When thispart functions adequately the peak current mode control subsystem of both sides, including theMOSFETs are soldered onto the PCB. Here the gate of both the MOSFETs are measured toverify whether the gate receives the expected PWM signal of around 12V. This is initially donewhile the current(Ilim) and voltage(Vsetp) are not connected. After this the transformer andclamp circuit are placed on the PCB. This is the first time to check whether the regulating partis working correctly. Since the voltage setpoint isn’t connected the output is supposed to takeon a constant value based on the voltage divider, described in section 2.1.

When the systems above are all working properly the other subsystems, described in section2.4 can be soldered onto the PCB. First, the direction comparator is connected, as alreadydescribed this subsystem has the function to control the direction of charging for the flyback.To check this the test-points DIR1 and DIR2 can be consulted, and based on the value of thesepins one of the IC’s needs to be turned off, while the other is in normal operation.

Secondly, the DAC is put in place. A reference PWM signal should be provided to check thelow pass filter of this system. Lastly, the measurement bridge is verified. To check whether thesystem is working properly the scale reduction and noise filtering needs to be checked.

If the board’s elements and subsystems are all working, the next step is verifying the require-ments. To serve as input and outputs of the converter, a power supply capable of 0-48V/3A isrequired, as well as some sort of dummy load as an electronic load or variable power resistorfor the output.

First of all, the large input/output voltage range and current limiting needs to be tested. Thisis done by supplying the input with a voltage that is slowly increased from 0V to 48V. Theconverter needs to switch on at 12V. A voltage between 0 and 5V is supplied to Vsetp in order tocheck the output voltage range. The current limiting needs to be tested by supplying an analogsignal to ILim. Other design specific requirements can be validated by checking various criticalvoltage signals as the shunt resistor voltage and the drain source voltage over the MOSFETs,as well as measuring overall system performance and efficiency


5.2 Prototype 32

5.2 Prototype

Figure 5-1 shows the prototype of the bi-directional flyback converter. The prototype consistsof the elements described in chapters 2 and 4. The input and output can be found at the 2screw terminals(A). The key components as described in chapter 2 are found near the centerof the board. The MOSFETs(B), the transformer(C) and the ICs(D) are all placed relativelyclose to each other. The subsystems are placed around these key elements. The power supplyis placed on the left side of the PCB(E), the measurement bridge can be found at (F), the di-rection comparator can be found at (G) and the Digital to Analog converter can be found at (H).

The prototype has a couple of items that should be mentioned before delving further intoevaluation of the circuit. First of all, the ground plane is missing, meaning that the groundconnections of the components needed to be soldered manually. Secondly, some footprintsappeared to be too small. This involved the shunt resistor, power supply capacitors and thetransformer. Thirdly, the prototype uses simple headers to connect the converter with themicrocontroller, which isn’t preferable when looking at mass production. Lastly, connections ofVsense1.1 and Vsense2.1 were switched and the placement of some test-points are odd.

Figure 5-1: Prototype of the flyback converter


5.3 Testing and Results 33

5.3 Testing and ResultsThe design requirements of section 1.3 are evaluated in this section and the results of thetransformer are shown.

Transformer results A transformer was winded according to the design described in section2.2.1. Using an impedance spectrum analyzer both the inductance, leakage inductance andAC resistance of both sides were measured. In the appendix the figures regarding these resultscan be found. The primary inductance was measured at 19.49 uH, the primary resistance at340 mΩ, the secondary inductance was measured at 19.77 uH and the secondary resistance at402mΩ.To measure the leakage inductance the secondary side of the transformer was short circuited asshown in figure 5-2. This way the reflected voltage is zero and the inductance measured is theleakage inductance. Same can be done for the secondary leakage inductance. The measurementresulted in Llk1 = 389, 3nH and Llk2 = 390, 4nH.

Figure 5-2: Measurement circuit for leakage inductance [26].

Voltage range and Current limit One of the first requirements to test is the large input andoutput voltage range. In order to be able to charge a variety of different batteries, as well asprovide versatility in application the range requirement was chosen from 12V to 48V. Ideally,the switching noise produced by the converter topology is filtered out as well. The converterstarts up when either one of the sides is fed with a voltage higher than 12V. The voltage appliedto the Vsetp input subsequently determines the output voltage that the IC regulates to. Figures5-3 and 5-4 show the input and output voltage lines. Evident is that the range requirementhas been met and it has been determined that the range is controllable with an analog signalbetween 0 and 5V. The ripple in the output voltage line is limited to an acceptable level, whichis a decent result.

Figure 5-3: Vin=48V, Vout=12V Figure 5-4: Vin=12V, Vout=48V

The current limit signal has been tested by connecting an analog DC signal to the ILim inputof the converter. The DC signal is super positioned onto the current measurement entering theIC. The current is successfully limited, and consequentially the converter does not turn on whenthe limit is set to minimum.



DCM operation The second requirement to test is the discontinuous operating mode of theconverter. This can be examined by looking at the current sense voltages over both shunt resis-tors.

Figure 5-5: DCM operation, Vin=24V, Vout=48V

Figure 5-5 shows these voltages with corre-sponding current axis. Yellow represents theprimary inductor current, and blue the sec-ondary inductor current. The switching fre-quency is 125kHz, the duty cycle is 50% (max)and the input and output voltages are 24Vand 48V respectively. The secondary currentdrops to zero well before the cycle ends, andthus the converter is working in DCM. Thesignal is very noise, which is probably due toa combination of factors including the groundplane, the measurement tools and the over-all PCB layout. According to equation 2-5:Ip,peak = V in·D

Lp·f = 24V ·0.520uH·125kHz = 4.8A

Which coincides with the actual current en-tering the primary inductor. If the K-factorwas 1, Ip,peak would equal Is,peak with the specifications of our transformer, N1 = N2 and Lp= Ls. This would result in a current fall-time duty cycle of:

D = Is,peak·Ls·fV out = 4.8A·20uH·125kHz

48V = 0.25

Subsequently, one would expect an RMS current at the secondary side of [34]:

IRMS = Is,peak ·√t13T = Is,peak ·

√D

3 = 1.39A (5-1)

Although the results show a promising waveform, Is,peak and D are not quite equal to thecalculated value. It can be concluded that the K-factor is probably not unity, the turns rationot equal to 1 and the primary and secondary inductance not equivalent. This is a result of themanual winding of the transformer.

Switching frequency The IC output gate signal and corresponding current sense input can beseen in figure 5-6. The IC has no trouble with a switching frequency of 125kHz, thus meeting oneof our wishes. The cause of the noise on the gate signal when it is low has not been found yet, butthe culprit is probably the bad ground connections and a too large pull-down resistor on the gate.

Figure 5-6: Vgs output and current sense signal

The current sense signal corre-sponds to the simulated signal insection 3 figure 3-2. Once again thenoise during switching is extremelyhigh due to the ground connectionsamong possible other origins, the ac-tive filter however does filter out asignificant amount of the noise, ifcompared to figure 5-5. In this mea-surement the current does not ex-ceed the maximum allowed current,and consequentially the IC outputsa maximum duty cycle PWM.



Power output The available power and voltage range of the converter largely determines thefunctionality and relevance of the product. As a requirement we wanted our converter to be ableto deliver at least 110W/48V. The obvious test to perform to measure the power performanceis to load the converter while the output voltage is set to 48V. Figure 5-7 shows the measuredI-V curve of this trial.

Evident is that the converter does not perform up to the required 110W (48V × 2A = 96W).As the current goes up, it reaches a point where the IC can no longer regulate the output to48V, and the output voltage starts to drop according to current drawn. The reason for thisvoltage drop is that the IC is at its maximum duty cycle limit of 50%, so the power transferfrom primary to secondary side can no longer increase without increasing the input voltage.Using the equations for power transfer in a flyback converter stated in section 2.2.1 and equa-tion 5-1, one can calculate the RMS output current at which the power transfer should saturate.

Figure 5-7: Power transfer saturation, Vin=48V

Our calculated RMS current andcorresponding power output far ex-ceeds the actual performance. Thus,the RMS current at the secondaryside is lower than expected, with agiven input voltage and 50% maxduty cycle. The cause of this prob-lem could be a number of things.First off, the current entering theprimary inductor during the ON-state could be less than predicted,resulting in an overall lower powertransfer saturation limit.Secondly, the resulting current inthe secondary inductor during theOFF-state could also prove to beless than calculated. This could becaused by unforeseen losses in thetransformer or MOSFET, or a higher secondary inductance than calculated and measured.This, in turn, would also explain the lower power transfer saturation of the converter.



Start-up and output signals The start-up procedure simulated in section 2-15 figure 3-3 wasreproduced during a test with the actual converter and can be seen in figures 5-8 and 5-9.The measurements were done on the analog output signals destined to connect to a micro-controller. The measurement bridge does its job and the analog voltage measurement signals(yellow) are fairly stable and noise-free. The analog current measurement signals (blue) arequite stable as well, filtering and amplifying the current sense voltages of figure 5-5. Evidentin the start-up figures is the output voltage being regulated to its final value, with a currentpeak coinciding with the rising edge of the output voltage. After the settling of the voltage, thenominal output current drops to a constant 0.2A. This clearly shows the likeness of the actualstart-up behaviour to the simulated behaviour. The secondary current measurement (I2) doesnot function as expected.

Vin=V1, Vout=V2

Figure 5-8: Start-up behaviour, V1/I1 Figure 5-9: Start-up behaviour, V2/I2

Bi-directional functionality A major driving force behind a large part of our converter designwas the bi-directional power transfer functionality. To realize this on the converter PCB, bothICs and MOSFETs have to work identically, the power transfer in the transformer should behaveindependent of direction, and the generated direction signal should turn off one of the IC’s whilerelinquishing control of the other. Figures 5-10 and 5-11 show the same start-up measurementsas figure 5-8 and 5-9, but performed in the other direction. Evident is the duality betweenV1/V2 and I1/I2, clearly illustrating the bi-directional functionality.

Vin=V2, Vout=V1

Figure 5-10: Start-up behaviour, V1/I1 Figure 5-11: Start-up behaviour, V2/I2



Controllability and Application The converter was designed in such a way that it would becontrollable by any type of microcontroller, and was also stated as a requirement in section1.3. The analog measurement output signals from the measurement bridge have been discussedand deemed functioning. The direction comparator subsystem has been tested and consideredworking. The last signal translation block is the DAC. Figures 5-12 and 5-13 show the DAC’sworking, smoothing out the ILim and Vsetp PWM signals to a steady DC-value between 0 and5V. The converter functions as expected with the DC control signals.

Figure 5-12: DAC of ILim Figure 5-13: DAC of Vsetp

This feature together with the bi-directionality satisfies another wish stated, which was thatthe converter is applicable in a variety of different circumstances, such as DC-smart grids orthe automotive industry. The relatively easy control makes the converter suitable for low-cost,highly-integrated smart DC-grids, as well as for novel, high-speed power control in automotivevehicles. The power output however, limits the functionality significantly.

Robustness and Durability A critical parameter and driving force of the design of the flybackconverter as stated in section 2.2.2, is the Vds over each MOSFET.

Figure 5-14: Vds over each MOSFET, Vin=48V,Vout=48V

Figure 5-14 shows the characteristic voltagesduring multiple switching cycles of our con-verter. The converter was tested with maxi-mum electrical conditions of Vin = 48V andVout = 48V, where the reflected Vds on theswitching MOSFET is highest (blue curve).The peak voltage measured is 154V, and oc-curs right after switching off the MOSFET.This is also the peak that one wants to clampfor a robust system. In our case, the cho-sen MOSFET can easily withstand this volt-age and we have therefore tested it withoutthe clamp circuit in place. For robustness itcould be considered to place the clamp circuitanyway, as this adds another level of safety.



For the sake of component durability we inspected our converter with a thermal camera. Theimage can be seen in figure 5-15, with the corresponding electrical conditions. Evident are 3hot spots, which coincide with the MOSFETs and the transformer (figure 5-1). The energy flowwas from right to left, so it is the switching MOSFET that is getting considerably warm. Theheat generated is directly proportional to the efficiency of the converter, so the temperature ofthe MOSFET would ideally be lower, but is not disastrous for the converter as the MOSFEThas a rated operating temperature of 175°C.

Figure 5-15: Thermal image, Vin=24V, Vout=24V, I=1AEfficiency The efficiency of the converter has not been stated as a requirement or wish and thedesign has therefore not been centered around efficiency. However, the efficiency of a converteris of interest to the circuit design and pcb layout subsystems as it provides feedback on theeffectiveness of the components, the placing of the components and traces, and yields someinsight into the operating environments and applications the converter will be suitable for. Arough estimation of the efficiency of our converter under different electrical circumstances canbe found in figures 5-16 and 5-17. Note that the efficiency does not exceed 80%, which can beseen as a fairly standard efficiency for non-optimized flyback converters [32].

Figure 5-16: Converter efficiency vs. outputcurrent, Vin=48V

Figure 5-17: Converter efficiency vs. outputcurrent, Vin=24V


5.4 Assessment 39

5.4 Assessment

Overall the design works fairly decent. Some requirements have been achieved, yet others remainto be met. The accomplishment are the following:

• Working bi-directional flyback SMPS topology.

• Full input and output voltage range of 12V to 48V, controllable by a single PWM signal.

• Fast, analog cycle-to-cycle current limiting.

• SMPS operating at 125kHz.

• Stable voltage measurements of input and output.

• Stable primary side current measurement.

• Maximum power transfer of 96W.

The requirements and wishes that remain to be met:

• Maximum power rating of 110W at Vin=48V, Vout=48V.

• Stable current measurement on the secondary side.

• High Efficiency

• General robustness and reliability.

The current prototype works with any input and output ranging from 12V to 48V. However, thepower output is still limited due to the power transfer saturation, and is not constant over theentire voltage range. The maximum power output lies at 96W with 48V input and output, withan efficiency of 75%. This is fairly close to the 110W target, but the efficiency is not as high asexpected. As for the measurements supplied to the microcontroller, all but the secondary sidecurrent measurements work. Due to the flyback topology, it is possible to reflect the primaryside measurements to the output by factoring in the non-ideal transformer and the circuit losses.

As for the high temperature produced by the MOSFET, it is not a major problem since theMOSFET can handle this, but for overall system efficiency, reliability and robustness it mightbe considered to add heat-sinks to the prototype. As for the general prototype robustness, theAUIRFR4620 MOSFET holds up to the high reflected voltages really well, but could be furtherprotected by adding the proposed clamp circuit design.

The power rating requirement has not been met. The causes discussed in section 5.3 are at-tributed to prototype design, but some mistakes could have been made in an earlier step ofmacro-circuit design or transformer design.

The secondary-side current measurement failed to work. After inspection it was discovered thatbecause of the current direction in the secondary shunt, the voltage potential of the currentmeasurement is negative with respect to ground. Since our op-amp measurement implementa-tion does not support negative voltages, the measurements are non-existent.


5.5 Next steps 40

5.5 Next steps

Considering what has been achieved up to this point, there is still more work to be done beforethis converter can be considered as a viable option for the solar-powered eBike charging station.

Fulfill remaining requirements The most important requirement to fulfill is to reach the powerrating of 110W. A possible solution to this, while not completely fixing the problem, is to lowerthe switching frequency. This increases the maximum power transfer of the converter. Thenegative side is that this is realized by increasing the peak currents in the transformer, thusproducing more electrical stress to the circuit.

Secondly, it is of importance to check what is affecting the efficiency and robustness. By takingthe generated heat and location into account, the source of the power loss can be detected.Using a more efficient MOSFET or transformer design might resolve this problem. Robustness,can be improved by applying the designed clamp circuit to the prototype and studying if thismight improve the high temperatures measured at the MOSFET.

As for the current measurement on the secondary side, to solve this problem a method wouldhave to be found with which the measurement bridge is also capable of measuring the negativevoltages of the secondary shunt, and consequentially producing a usable current measurement.

Prototype improvements There are surely four points where the current prototype PCB canbe improved; the ground-plane, footprints/components, heat dissipation and electrical connec-tions. For the ground-plane, make sure that it is included in the prototype seeing that a goodground connection has a big influence on the noise reduction, IC stability and overall systemfunctioning. Furthermore, it is important to make sure the footprints on the PCB are all correctand easy to perform tests on. Some of our footprints were designed wrong, making the solderingand testing more difficult than it could be.Some traces on the prototype were connected falsely on the PCB design. This can of coursealways occur when designing the first prototype of a PCB, but these must be noticed and dealtwith accordingly. Lastly, making the MOSFET on the PCB compatible with a heatsink wouldbe ideal for optimizing the system in further stages.

Manufacturing considerations Although it is essential to first get the design completely work-ing, for further production of this converter the following might be essential in making the designmanufacturing ready.

• The PCB size, and simultaneously the manufacturing price can be reduced by replacing allof the components by their surface-mount device (SMD) variant. This not only decreasessize, but also positively influences the functioning of the converter by optimizing criticalcurrent paths.

• A housing should be designed, together with standardized connectors if the converter isto be used in the field.

• If the converter is to be brought on the market, EMI tests have to be passed. This involvesa critical rethinking of the EMI reduction on the PCB.


Bibliography

[1] Sergio Saponara, Luca Fanucci, Edoardo Biagi and Riccardo Serventi Hard macrocells forDC/DC converter in automotive embedded mechatronic systems, EURASIP Journal onEmbedded Systems, 2016

[2] TU Delft Campus Green Village, http://www.sustainability.tudelft.nl/projects/campus/

[3] Mr.S.Dhanasekaran, Mr.E.Sowdesh Kumar and Mr.R.Vijaybalaji, Multiple Output SMPSwith Improved Input Power Quality, Department of Electrical Engineering, Indian Instituteof Technology, Delhi,2010

[4] G. M. Ponzo, G. Capponi, P. Scalia and V. Boscaino, An Improved Flyback Converter,University of Palermo, May 2009

[5] Jean Picard, Under the hood of flyback SMPS design Texas Instruments Power SupplyDesign Seminar, 2010

[6] J. Formenti and R. Martinez, Design Trade-offs for Switch-Mode Battery Charger, TexasInstrument, 2004, pg. 1-2.

[7] Transformer datasheet EPCOS,https://en.tdk.eu/inf/80/db/fer_07/etd_29_16_10.pdf

[8] Colonel Wm. T. McLyman, Transformer and Inductor Design Handbook, 3rd ed., MarcelDekker, Inc, 2004.

[9] Dr.-Ing. Arthur Seibt, Vienna, The Flyback DC-DC Converter, Bodo’s Power Systems,October 2016, pg. 62-69.

[10] Dr.-Ing. Arthur Seibt, Vienna, The Flyback DC-DC Converter, Bodo’s Power Systems,November 2016, pg. 70-83.

[11] Henry J. Zhang, PCB Layout Considerations for Non-Isolated Switching Power Supplies,Application note 136, Linear Technology, June 2012

[12] Sameer Kelkar, The Fundamentals of Flyback Power Supply Design, Power Integrations,Inc. (San Jose, CA) , 2012.

[13] Wikipedia, the free encyclopediahttps://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)


http://www.sustainability.tudelft.nl/projects/campus/

http://www.sustainability.tudelft.nl/projects/campus/

https://en.tdk.eu/inf/80/db/fer_07/etd_29_16_10.pdf

https://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)

42

[14] Infineon Technologies, Automotive MOSFETs: Prouct Overview, 2016

[15] Hangseok Choi, Ph. D, Practical Feedback Loop Design Considerations for Switched ModePower Supplies, Fairchild Semiconductor Power Seminar, 2010 - 2011.

[16] H. Dean Venable, The K Factor: A new mathematical tool for stability analysis and syn-thesis, Venable Industries, Inc, 1983.

[17] Introduction to SMPS Control Techniques, Microchip Technology, inc., WebSeminar, 2006.

[18] Loyd Dixon, Designing planar magnetics, Texas Instruments.

[19] Delta, TU Delft,http://www.ridleyengineering.com/design-center-ridley-engineering.html

[20] Loyd H. Dixon, Jr Eddy Current Losses in Transformer Windings and Circuit Wiring,Texas Instruments, 2003.

[21] Gwan-Bon Koo/ Ph. D Application Note AN-4147: Design Guidelines for RCD Snubberof Flyback Converters, Fairchild Semiconductor, 2006.

[22] Ashraf A. Mohammed and Samah M. Nafie Flyback Converter Design for Low PowerApplication, Sudenese Electricity Distribution Company.

[23] Andrew Smith Calculating power loss in switching MOSFETs, Power Integrations, Inc.,2011.

[24] Toshiba Corporation. Power MOSFET: Selecting MOSFETs and Consideration for CircuitDesing, 2016.

[25] Gurkan Tosun, Omer Cihan Kivanc, Ender Oguz, Ozgur Ustun, and R. Nejat TuncayDevelopment of High Efficiency Multi-Output Flyback Converter for Industrial Applications

[26] VOLTECHNOTES Measuring Leakage Inductance, Voltech Instruments Ltd., 2001.

[27] Hector Ortega Jimenez AC resistance evaluation of foil, round and Litz conductors,Chalmer’s university of technology, 2013.

[28] Henry J. Zhang, PCB Layout Considerations for Non-Isolated Switching Power Supplies,Linear Technology, Application note 136, June 2012.

[29] Infineon Technologies, HEXFET power MOSFETs, AUIRFR4620 datasheet, May 2015.

[30] Texas Instruments, Current Mode PWM Controller, UC2845N datasheet, May 2002.

[31] Texas Instruments, Switching Voltage Regulators, LM2575HV datasheet, April 2013.

[32] Brian Huffman, Efficiency and Power Characteristics of Switching Regulator Circuits, Lin-ear Technology, Application note 46, November 1991.

[33] Ken Kundert, Power Supply Noise Reduction, The Designer’s Guide Community, Version4, January 2004.

[34] Adrian Nastase, https://masteringelectronicsdesign.com/how-to-derive-the-rms-value-of-a-triangle-waveform/.

[35] BAP group B1, Control Network of Bi-Directional DC/DC Converters, TU Delft, June2017.


http://www.ridleyengineering.com/design-center-ridley-engineering.html

http://www.ridleyengineering.com/design-center-ridley-engineering.html

https://masteringelectronicsdesign.com/how-to-derive-the-rms-value-of-a-triangle-waveform/

https://masteringelectronicsdesign.com/how-to-derive-the-rms-value-of-a-triangle-waveform/

Appendix

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

D D

C C

B B

A A

Title



6.8K

R29

2.2nFC37

R28

C31

C33

Q3

12V

R35R34

C365V

0.01ΩR23

1k

R18

1nFC28

Imeas1

Imeas1

R48R47

C455V

0.01ΩR24

1k

R19

1nFC27

Imeas2

Imeas2

300kR11

30kR17

300kR13

30kR21

300kR10

30kR16

300kR12

30kR20

47pFC21

47pFC20

47pFC24

47pFC23Vsense1.1

Vsense2.1

Vsense2.1820uFC22

R44

C43

C44

6.8K

R45

2.2nFC46

Q4Vsense1.1

12V

R27ILim

R40ILim

20k

R46Vsetp

20k

R30Vsetp

GateOut1

GateOut2

Vsense1.2Vsense2.2

100kR33

100kR43

5V

6.7uF C38

6.7uF C47

1KR39 2.2K

R36DIR

ON/OFF2

ON/OFF1

ON/OFF2

ON/OFF1

Vref1

Vref2

Vref2

Vref1

10KR25

Vsense1.2100nF

C30

5V

5V

10KR37

Vsense2.2100nF

C39

Vout1

Vout2

V1+

V1-

V2+

V2-


VsetpPWM

ILimPWM

5V

5V

1K

R8

1K

R22

330nFC29

330nFC18

Vsetp

ILim

DAC's

Isense2

Isense1

5V

5V

Imeas1

Imeas2

R42

C41R41

R32C34

R31

10K

R26

10K

R38

100nFC32

100nFC40

Iout1

Iout2

Measurement Bridge


10Ω

R14

10Ω

R15GateOut1

GateOut2

V1


Transformer

V1+

V2+L1 12V

C5C4C3 C8

Power Distribution

3

21

84 U4A

MCP602-I/P

3

21

84 U5A

MCP602-I/P

75

6

84 U4B

MCP602-I/P

75

6

84 U5B

MCP602-I/P

3

21

84

U7A

3

21

84

U8A

330uFC2

C7

12

V1

12

V2

V1+V1-

V2-V2+

820uFC19

1 23 45 67 89 1011 1213 14

Control Signals

Header 7X2


Connectors

C48 C49 C50

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U6

UC2845N

COMP1

VFB2 ISENSE 3

RT/CT 4

GROUND 5

OUTPUT 6

VCC7

VREF 8

U9

UC2845N

31

84

2 1 U12ALM393P

6

572

84

U12BLM393P

5V

5V

31

84

2 1U3ALM393P

6

572

84

U3BLM393P

1V56

1V56

1V56

2.7k R9

2.7kR7

5V

D69

12V

V1 V2

Gate1 Gate2

GND1 GND6

DIR1

DIR2

Vsetp

ILim

1MR49

1MR50

5V

GND2 GND3 GND4GND5

D10LED1

R51

GateOut1 GateOut2

5V

V1-Shield S

VCC 1D- 2

D+ 3GND 4

J1

USB B

R52R53

R54

VsetpPWMILimPWM

DIR

5V

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U2 LM2575HVT-12

100uFC10

Input1

GN

D3

ON

/OFF

5

Output 2

Feedback 4

U1 LM2575HVT-5

100uFC1

330uFC9

L2 PI5V01 CO5V

PI12V01 CO12V

PIC101


COC2 PIC301

PIC302 COC3 PIC401

PIC402 COC4 PIC501

PIC502 COC5


PIC802 COC8

PIC901 PIC902

COC9 PIC1001

PIC1002 COC10

PIC1801

PIC1802 COC18

PIC1901

PIC1902

COC19

PIC2001

PIC2002 COC20

PIC2101


PIC2202

COC22 PIC2301

PIC2302 COC23

PIC2401

PIC2402 COC24

PIC2701

PIC2702 COC27

PIC2801

PIC2802 COC28

PIC2901

PIC2902 COC29

PIC3001


COC31

PIC3201

PIC3202 COC32

PIC3301 PIC3302

COC33


PIC3601 PIC3602

COC36

PIC3701

PIC3702 COC37

PIC3801

PIC3802 COC38

PIC3901

PIC3902 COC39

PIC4001

PIC4002 COC40


PIC4301 PIC4302

COC43

PIC4401 PIC4402

COC44

PIC4501 PIC4502

COC45

PIC4601

PIC4602 COC46

PIC4701 PIC4702

COC47

PIC4801



PIC5002 COC50








COControl Signals

PID101 PID102

COD1

PID201 PID202

COD2

PID301 PID302

COD3

PID401 PID402

COD4

PID501 PID502

COD5

PID601 PID602

COD6

PID701 PID702

COD7

PID801 PID802

COD8 PID901 PID902

COD9

PID1001 PID1002


COD11

PID6901 PID6902

COD69

PIDIR101 CODIR1

PIDIR201 CODIR2

PIGate101 COGate1

PIGate201 COGate2

PIGND101 COGND1

PIGND201 COGND2

PIGND301 COGND3

PIGND401 COGND4

PIGND501 COGND5

PIGND601 COGND6

PIILim01 COILim

PIInput01

COInput

PIJ101

PIJ102

PIJ103

PIJ104

PIJ10S

COJ1

PIL101 PIL102

COL1 PIL201 PIL202

COL2

PIQ101 PIQ102

PIQ103 COQ1

PIQ201 PIQ202

PIQ203 COQ2

PIQ301 PIQ302

PIQ303

COQ3

PIQ401 PIQ402

PIQ403

COQ4

PIR701

PIR702

COR7

PIR801 PIR802

COR8

PIR901

PIR902

COR9

PIR1001

PIR1002 COR10

PIR1101

PIR1102 COR11

PIR1201

PIR1202 COR12

PIR1301

PIR1302 COR13

PIR1401 PIR1402


COR15

PIR1601

PIR1602 COR16

PIR1701

PIR1702 COR17

PIR1801 PIR1802


COR19 PIR2001

PIR2002 COR20

PIR2101

PIR2102 COR21

PIR2201 PIR2202

COR22

PIR2301

PIR2302 COR23

PIR2401

PIR2402 COR24

PIR2501 PIR2502

COR25



PIR2801 PIR2802


COR29

PIR3001 PIR3002


PIR3201 PIR3202

COR32

PIR3301

PIR3302

COR33

PIR3401 PIR3402


COR35

PIR3601 PIR3602

COR36

PIR3701 PIR3702

COR37


PIR3901

PIR3902

COR39

PIR4001 PIR4002

COR40


PIR4201 PIR4202

COR42

PIR4301

PIR4302 COR43

PIR4401 PIR4402


COR45




PIR4901

PIR4902

COR49 PIR5001

PIR5002

COR50

PIR5101

PIR5102 COR51

PIR5201

PIR5202

COR52 PIR5301

PIR5302

COR53 PIR5401

PIR5402

COR54

PITransformer00

PITransformer01

PITransformer02


PIU101 PIU102

PIU103

PIU104

PIU105

COU1

PIU201 PIU202

PIU203

PIU204

PIU205

COU2

PIU301

PIU302

PIU303

PIU304

PIU308

COU3A

PIU304

PIU305

PIU306

PIU307

PIU308

COU3B

PIU401

PIU402

PIU403

PIU404

PIU408

COU4A

PIU404 PIU405

PIU406

PIU407

PIU408

COU4B

PIU501

PIU502

PIU503

PIU504

PIU508

COU5A

PIU504 PIU505

PIU506

PIU507

PIU508

COU5B

PIU601

PIU602 PIU603

PIU604

PIU605

PIU606

PIU607

PIU608

COU6

PIU701

PIU702

PIU703

PIU704

PIU708 COU7A

PIU801

PIU802

PIU803

PIU804

PIU808 COU8A

PIU901

PIU902 PIU903

PIU904

PIU905

PIU906

PIU907

PIU908

COU9

PIU1201

PIU1202

PIU1203

PIU1204

PIU1208

COU12A

PIU1204

PIU1205

PIU1206

PIU1207

PIU1208

COU12B

PIV101 COV1

PIV101

PIV102

PIV201 COV2

PIV201

PIV202

PIVsetp01 COVsetp

PIR3602 PIR3901

PIU302

PIU306

PIU1202

PIU1205

NL1V56

PI5V01


PIJ101

PIL202

PIR701

PIR901

PIR3302 PIR3601

PIR4302

PIR5101

PIR5302

PIU104

PIU308

PIU408

PIU508

PIU708

PIU808

PIU1208

NL5V

PI12V01 PIC201

PIC3801

PIC4701

PIL102

PIU204

PIU607

PIU907


PIR5401

PIU1203

PIU1206

NLDIR

PIGate101

PIR1401

PIU606


PIR1502

PIU906

NLGateOut2

PIC2902

PIILim01 PIR2201

PIR2702

PIR4002

NLILim


PIR5301

PIU305

NLILimPWM

PIC2802 PIR1802

PIR2701

PIU405

PIU703

NLImeas1

PIC2702 PIR1901

PIR4001

PIU505

PIU803

NLImeas2

PIC3202


PIR2602 NLIout1

PIC4002


PIR3802 NLIout2

PIC3602

PIQ303

PIR3401

PIU603 PIU701

NLIsense1

PIC4501

PIQ403

PIR4701

PIU801 PIU903

NLIsense2

PIC101 PIC1001

PID102

PID202

PIInput01

PIU101

PIU201


PIC3102

PIC3302

PIU601

PIC3301 PIR2801

PIC3401

PIR3102 PIR3201

PIU406

PIC3402

PIR2601

PIR3202

PIU407

PIC3601

PIR3402 PIR3501

PIU702

PIC3702

PIR2902

PIU604


PIC4101

PIR4102 PIR4201

PIU506

PIC4102

PIR3801

PIR4202

PIU507

PIC4302

PIC4402

PIU901

PIC4401 PIR4401

PIC4502

PIR4702 PIR4801

PIU802

PIC4602

PIR4502

PIU904


PID401


PID802 PID501


PID902


PIR2302


PIR2402

PID1001 PIR5102


PIJ102

PIJ103

PIJ104

PIQ102

PIR1402

PIR5001 PIQ202

PIR1501

PIR4901



PIDIR101 PIQ302

PIR3301 PIU1201

NLON0OFF1

PIDIR201 PIQ402

PIR4301

PIU1207 NLON0OFF2

PIC1901 PIC2002 PIC2102

PID101

PID801

PIR1002 PIR1102


PIV102 NLV10

PIC2201 PIC2302 PIC2402

PID201

PID901

PIR1202 PIR1302

PITransformer01

PIV201 NLV20

PIC102 PIC202


PIC1801

PIC1902 PIC2001 PIC2101 PIC2202

PIC2301 PIC2401

PIC2701 PIC2801 PIC2901

PIC3001 PIC3201

PIC3701

PIC3802

PIC3901 PIC4001

PIC4601 PIC4702


PID1101

PID6901


PIJ10S

PIR1601 PIR1701 PIR2001 PIR2101

PIR2301 PIR2401

PIR3101

PIR3502

PIR3902

PIR4101

PIR4802

PIR4902 PIR5002

PIR5202 PIR5402


PIU304

PIU404

PIU504 PIU605

PIU704

PIU804

PIU905

PIU1204

PIV101

PIV202

NLV10

NLV20


PIU401

PIU402

NLVout1


PIU501

PIU502

NLVout2

PIQ301

PIR2901 PIU608

NLVref1

PIQ401

PIR4501 PIU908

NLVref2

PIC4301

PIR1001

PIR1602

PIR4402

PIR4602

PIU902

NLVsense101 PIR1101

PIR1702

PIR2502

NLVsense102 PIC3101

PIR1201

PIR2002

PIR2802

PIR3002

PIU602

NLVsense201

PIR1301

PIR2102

PIR3702

NLVsense202


PIR3001

PIR4601

PIVsetp01 NLVsetp


PIR5201

PIU303

NLVsetpPWM

Figure A-1: Altium schematic of the bi-directional flyback converter


44

PA5V01 CO5V

PA12V01 CO12V

PAC101

PAC102 COC1

PAC201

PAC202

COC2

PAC301

PAC302 COC3

PAC401 PAC402

COC4

PAC501 PAC502 COC5

PAC701

PAC702

COC7

PAC801

PAC802 COC8

PAC902

PAC901 COC9

PAC1002

PAC1001

COC10

PAC1801 PAC1802

COC18

PAC1902

PAC1901

COC19

PAC2001

PAC2002 COC20

PAC2101

PAC2102

COC21

PAC2202

PAC2201

COC22

PAC2302

PAC2301 COC23

PAC2402

PAC2401 COC24

PAC2702

PAC2701

COC27

PAC2801 PAC2802 COC28



PAC3102 PAC3101

COC31


PAC3302 PAC3301

COC33

PAC3402

PAC3401 COC34


PAC3702 PAC3701

COC37 PAC3802

PAC3801 COC38


PAC4002 PAC4001

COC40


PAC4302

PAC4301

COC43 PAC4402

PAC4401

COC44

PAC4502

PAC4501 COC45

PAC4602 PAC4601

COC46

PAC4702

PAC4701 COC47


PAC4902

PAC4901 COC49

PAC5002

PAC5001

COC50

PAControl Signals01

PAControl Signals02

PAControl Signals03

PAControl Signals04

PAControl Signals05

PAControl Signals06

PAControl Signals07

PAControl Signals08

PAControl Signals09

PAControl Signals010





COControl Signals

PAD102 PAD101 COD1

PAD202 PAD201 COD2

PAD302

PAD301

COD3

PAD402

PAD401

COD4

PAD502

PAD501

COD5

PAD603

PAD602

PAD601

COD6

PAD703

PAD702

PAD701

COD7

PAD801

PAD802

COD8

PAD901

PAD902

COD9

PAD1002

PAD1001 COD10

PAD1101

PAD1102

COD11

PAD6901

PAD6902 COD69

PADIR101

CODIR1

PADIR201

CODIR2

PAGate101

COGate1

PAGate201

COGate2

PAGND101 COGND1

PAGND201 COGND2

PAGND301

COGND3

PAGND401

COGND4

PAGND501

COGND5

PAGND601

COGND6

PAILim01 COILim

PAInput01

COInput

PAJ10M

PAJ10S PAJ105 PAJ104 PAJ101 PAJ102 PAJ103

COJ1

PAL101

PAL102

COL1

PAL201

PAL202

COL2 PAQ102 PAQ103

PAQ101 COQ1

PAQ202 PAQ203

PAQ201 COQ2

PAQ301 PAQ302

PAQ303 COQ3

PAQ401 PAQ402

PAQ403 COQ4

PAR702 PAR701 COR7

PAR802 PAR801 COR8

PAR902 PAR901 COR9

PAR1002

PAR1001

COR10

PAR1102

PAR1101

COR11

PAR1201

PAR1202 COR12

PAR1301

PAR1302 COR13

PAR1402

PAR1401

COR14

PAR1501

PAR1502

COR15

PAR1602

PAR1601

COR16

PAR1702

PAR1701

COR17

PAR1802

PAR1801 COR18

PAR1901 PAR1902 COR19

PAR2001

PAR2002

COR20

PAR2101

PAR2102

COR21

PAR2202 PAR2201

COR22

PAR2302

PAR2301

COR23 PAR2401 PAR2402 COR24


PAR2601

PAR2602

COR26 PAR2701 PAR2702 COR27

PAR2801

PAR2802

COR28

PAR2901

PAR2902

COR29

PAR3001

PAR3002

COR30

PAR3101

PAR3102

COR31

PAR3201

PAR3202 COR32





PAR3702

PAR3701

COR37



PAR4001

PAR4002 COR40

PAR4101 PAR4102

COR41




PAR4501

PAR4502

COR45

PAR4601

PAR4602

COR46

PAR4701

PAR4702

COR47





PAR5202 PAR5201 COR52 PAR5302 PAR5301 COR53

PAR5402

PAR5401

COR54

PATransformer03

PATransformer01

PATransformer00

PATransformer02

COTransformer

PAU105 PAU104

PAU103

PAU101 PAU102

COU1

PAU205 PAU204

PAU203

PAU201 PAU202

COU2

PAU301

PAU302

PAU303

PAU304

PAU308

PAU307

PAU306

PAU305

COU3

PAU405

PAU406

PAU407

PAU408

PAU404

PAU403

PAU402

PAU401

COU4

PAU505

PAU506

PAU507

PAU508

PAU504

PAU503

PAU502

PAU501 COU5

PAU605

PAU606

PAU607

PAU608

PAU604

PAU603

PAU602

PAU601

COU6

PAU705

PAU706

PAU707

PAU708

PAU704

PAU703

PAU702

PAU701

COU7

PAU805

PAU806

PAU807

PAU808

PAU804

PAU803

PAU802

PAU801

COU8 PAU905

PAU906

PAU907

PAU908

PAU904

PAU903

PAU902

PAU901 COU9

PAU1201

PAU1202

PAU1203

PAU1204

PAU1208

PAU1207

PAU1206

PAU1205

COU12

PAV102

PAV101

COV1

PAV101

PAV202

PAV201 COV2

PAV201

PAVsetp01

COVsetp

PAR3602

PAR3901

PAU302

PAU306

PAU1202

PAU1205

PA5V01

PAC302

PAC402

PAC502

PAC701 PAC802

PAC901

PAC4802

PAC4902

PAC5002

PAJ101

PAL202

PAR701

PAR901

PAR3302

PAR3601

PAR4302

PAR5101

PAR5302

PAU104

PAU308

PAU408

PAU508

PAU708

PAU808

PAU1208

PA12V01

PAC201

PAC3801

PAC4701

PAL102

PAU204

PAU607

PAU907



PAR5401

PAU1203 PAU1206

PAGate101

PAR1401 PAU606

PAGate201

PAR1502 PAU906

PAC2902

PAILim01

PAR2201

PAR2702

PAR4002



PAR5301

PAU305

PAC2802

PAR1802

PAR2701 PAU405

PAU703

PAC2702

PAR1901

PAR4001

PAU505

PAU803

PAC3202

PAControl Signals05

PAControl Signals06

PAR2602

PAC4002

PAControl Signals07

PAControl Signals08

PAR3802 PAC3602

PAQ303

PAR3401

PAU603

PAU701

PAC4501

PAQ403

PAR4701 PAU801 PAU903

PAC101

PAC1001

PAD102

PAD202

PAInput01

PAU101

PAU201

PAC3002

PAR2501 PAU403

PAC3102

PAC3302

PAU601

PAC3301 PAR2801

PAC3401

PAR3102

PAR3201

PAU406 PAC3402

PAR2601 PAR3202 PAU407

PAC3601

PAR3402

PAR3501

PAU702 PAC3702 PAR2902

PAU604

PAC3902

PAR3701

PAU503

PAC4101

PAR4102

PAR4201 PAU506

PAC4102

PAR3801

PAR4202

PAU507

PAC4302 PAC4402

PAU901

PAC4401

PAR4401

PAC4502

PAR4702

PAR4801

PAU802

PAC4602

PAR4502 PAU904

PAD302

PAL101

PAU202

PAD401 PAD801

PAD501 PAD901

PAD601

PAQ103 PAR1801 PAR2302

PAD602

PAD802

PAQ101

PATransformer02

PAD701

PAQ203 PAR1902

PAR2402

PAD702

PAD902

PAQ201

PATransformer00

PAD1001

PAR5102

PAD1102 PAL201 PAU102

PAQ102 PAR1402

PAR5001

PAQ202 PAR1501

PAR4901

PAR702

PAR802

PAU301

PAR902

PAR2202 PAU307

PADIR101

PAQ302

PAR3301

PAU1201 PADIR201

PAQ402

PAR4301 PAU1207

PAC1901 PAC2002 PAC2102

PAD101

PAD402 PAR1002 PAR1102

PATransformer03

PAV101

PAV102

PAC102

PAC202

PAC301

PAC401

PAC501

PAC702 PAC801

PAC902

PAC1002

PAC1801

PAC1902 PAC2001 PAC2101

PAC2202 PAC2301 PAC2401

PAC2701

PAC2801

PAC2901

PAC3001 PAC3201

PAC3701

PAC3802

PAC3901

PAC4001

PAC4601

PAC4702

PAC4801

PAC4901

PAC5001

PAD301

PAD1002

PAD1101 PAD6901

PAGND101 PAGND201

PAGND301 PAGND401

PAGND501

PAGND601

PAJ10S

PAR1601 PAR1701 PAR2001 PAR2101

PAR2301

PAR2401

PAR3101

PAR3502

PAR3902

PAR4101

PAR4802

PAR4902

PAR5002

PAR5202

PAR5402

PAU103

PAU105

PAU203

PAU205

PAU304

PAU404

PAU504

PAU605

PAU704

PAU804

PAU905

PAU1204

PAV101 PAV202

PAC2201 PAC2302 PAC2402

PAD201

PAD502 PAR1202 PAR1302

PATransformer01

PAV201

PAControl Signals01

PAControl Signals02

PAU401

PAU402

PAControl Signals03

PAControl Signals04

PAU501

PAU502

PAQ301

PAR2901 PAU608

PAQ401 PAR4501

PAU908

PAC3101

PAR1001 PAR1602

PAR2802 PAR3002 PAU602

PAR1101 PAR1702

PAR2502

PAC4301

PAR1201 PAR2002

PAR4402

PAR4602 PAU902

PAR1301 PAR2102

PAR3702

PAC1802

PAD6902

PAR801

PAR3001

PAR4601

PAVsetp01

PAControl Signals09


PAR5201

PAU303

Figure A-2: Altium PCB of the bi-directional flyback converter


45

UC2845 block diagram

R15 10k

ROAD 200RV1 48

+

-

R14 9k

-+OA

+

-

Comp -

+

OA

R

S

Q

Vea

Vpeak

A

Figure A-3: Block diagram implementation of the UC2845 internal control loop

Figure A-4: Measurement of primary inductance at 125KHz L1 = 19, 49µH and R1 = 340, 69mΩ


46

Figure A-5: Measurement of secondary inductance at 125KHz L2 = 19, 77µH and R2 =402, 35mΩ


Errata

1. From the appendix, figures A-4 and A-5 have been corrected to figures A-6 and A-7.

Figure A-6: Copper, 1.25mm, primary inductance, @125KHz, L1 = 19, 49µH and R1 =340, 69mΩ


48

Figure A-7: Copper, 1.25mm, secondary inductance, @125KHz, L2 = 19, 77µH and R2 =402, 35mΩ

2. The formulas stated in section 2.2.1 are based on the paper from Seibt[9], [10]. Further-more, In section 2.2.1, an initial estimation is made regarding the resistance of the wire.However, there is another factor that could be calculated which is the resistance of thecore itself. The resistance of the core is a constant based on the dimensions of the coreand the gap. The following formula is valid,

Rm =leµr

+ lg

µo ·Ae(A-1)

with,

• Rm, resistance of the core• e, effective length of the core• µr, permeability of the core• lg, effective length of the air gap• µo, permeability in free space


bas van der werk, thomas gerrits & george koolman

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