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Topic 1

Power supply unit

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COURSE LEARNING OUTCOMES

(CLO)

CLO1. explain correctly the principles of electronic

circuits by using block diagram or circuit diagram (C4 -Analysis)

CLO2. conduct the construction of electronic circuits

application during practical works based on the theory

and principle operation of the circuits. (P4 - Mechanics)

CLO3. deliver an oral presentation to display goodcommunication skills. (A2Response to phenomena)


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LEARNING OUTCOMES

Upon completion of this topic students should be able to:

Explain the operation of a DC power supply circuit1.1

Explain applications of rectifiers1.2

1.3

1.4

1.5

Explain applications of filter

Explain applications about voltage regulator

Explain applications about voltage divider

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Power Supply

All electronic circuits need a power source towork.

For electronic circuits made up of transistorsand/or ICs, this power source must be a DCvoltage of a specific value.

A battery is a common DC voltage source forsome types of electronic equipmentespecially portables like cell phones andiPods.

Most non-portable equipment uses powersupplies that operate from the AC power linebut produce one or more DC outputs.


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Power supply unit

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Power supply unit

The functionsof power supply unit is

to convert the signal form AC input

power to DC power.A power supplyunit built with five major parts:

transformer, rectifier, filter, regulator

and voltage divider.

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Function of each block

TransformerReduce the value of the input acvoltage.

RectifierA circuit that converts ac voltage to dc

voltage

FilterThe main task of filter is to convert the

voltage at pulse to the voltage rippled

RegulatorVoltage regulator circuit is used to

reduced the difference to zero Voltage dividerCircuit is needed in power

supplies for electronic equipment requires.

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Output waveform from each block

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Transformer

Built from two winding transformer primary

and secondary loops. Network is to

separate the secondary circuit of the ac

supply lines high. This isolation canprevent a user from the secondary ac

voltage electric shock high. Separation of

the primary circuit is able to avoid theeffects of damage received in the

secondary winding circuit.

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Transformer

Transformer has a primary winding and

secondary winding. The ratio of the

number of turns in the primary to the

secondary number of turns is thetransformer turns ratio.

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Transformer

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Transformer

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Voltage ratio is proportional to the voltage induced in

the primary to the secondary winding turns.


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Transformer

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When the number of secondary winding

turns slightly compared to primary, lower

secondary voltage from the voltage in the

primary. Secondary voltage can becalculated.


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Transformer

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Function of Transformer

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Question

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Solution

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Diode

What is the

function of diode?

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2/12013


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Functions of diode

Switch

Clipper

Rectifier Clamp

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Schematic diagram and physical

structure of a diode

2.1 Understand the Characteristics ofdiode as a semiconductor

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OPERATION DIODE DURING

FORWARD & REVERSE BIASED

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APPLICATIONS OF DIODE

1. RECTIFIER

Rectifier is the circuit that used one or more diode to

convert the AC voltage to the pulsating dc voltage

There is 3 type of rectifiers :-

i) Half wave rectifier

ii) Full wave rectifieriii)Bridge rectifier

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Half-wave rectifier

Half-wave rectifier

Output Voltage

Input Supply Voltage

Operation

During the positive circle of input supply, diode D is in forward

biased and act as close switch. So the current can flow through it. ,

producing an output voltage as shown above.During the negative circle of the input supply, diode is reverse

bias and act as open switch, so the current cant flow through diode.

No voltage appears at output.

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How Rectifiers Work

The simplest form of rectifier isthe half wave rectifier shown.

Only the transformer, rectifierdiode, and load (RL) are shownwithout the filter and othercomponents.

The half wave rectifier produces

one sine pulse for each cycle ofthe input sine wave.

When the sine wave goespositive, the anode of the diodegoes positive causing the diodeto be forward biased. The diode

conducts and acts like a closedswitch letting the positive pulseof the sine wave to appearacross the load resistor.


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How Rectifiers Work (continued)

When the sine wave goesnegative, the diode anode will

be negative so the diode will bereverse biased and no currentwill flow.

No negative voltage will appearacross the load. The load

voltage will be zero during thetime of the negative half cycle.

See the waveforms that showthe positive pulses across theload. These pulses need to beconverted to a constant DC.


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The output DC voltage of a half wave rectifier can be

calculated with the following two ideal equations

rmsroot mean square

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Question

A half-wave rectifier circuit to the input

voltage 20 Vp-p, 50 Hz. Assuming no

voltage drop across the diode, calculate: -

i) the output signal voltage rectifier

ii) the output signal frequency

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Solution

Vm = 20 Vp-p

= 10 Vp

then VK = 10 Vp

Output signal frequency = Frequency of the input signal

= 50 Hz

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The average (av) and root-mean-square (rms) output voltages

of an ideal single phase full wave rectifier can be calculatedas:

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Consider the first half-cycle, when the source voltage polarity

is positive (+) on top and negative (-) on bottom. At this time,

only the top diode is conducting; the bottom diode is blocking

current, producing only positive half-cycle of the input supplyappears at load as shown at the above figure

R

Input supply Output voltage

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During the next half-cycle, the AC polarity reverses. Now, the

other diode (bottom) and the other half of the transformer'ssecondary winding carry current to the load resistor, producing

the same polarity of voltage as before (Figure below)

R

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2.2 Know diode

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Full-wave rectifier bridge rectifier

applications as rectifiers

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During positive half-cycle

D1

D3

D1 and D3 conduct, allowing the current

flowing to the load, RL. Load voltage appears at

load as shown at above figure.

RL

Load voltage

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During negative half-cycle

D2

D4

Load Voltage

D2 and D4 conduct, allowing the current

flowing to the load, RL. Load voltage appears at

load as shown at above figure.

RL

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Question

A full-wave rectifier circuit to the input

voltage 20 Vp-p 50 Hz. Used transformer

has a turns ratio 2:1. Assuming no voltage

drop across the diode, calculate: -

i) the output signal voltage rectifier

ii) the output signal frequency

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Solution

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Bridge Rectifier

Another widely used rectifier isthe bridge rectifier. It uses four

diodes. This is called a full wave rectifier

as it produces an output pulsefor each half cycle of the inputsine wave.

On the positive half cycle of theinput sine wave, diodes D1 andD2 are forward biased so act asclosed switches appearing inseries with the load.

On the negative half cycle,

diode D1 and D2 are reversebiased and diodes D3 and D4are forward biased so currentflows through the load in thesame direction.


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FILTER

The main task of the filter is to convert the

voltage pulse to a.t. rippling. The best filter

circuit is a filter that can reduce as much

as possible the value of Vr pp dc voltageproduced by rippling.

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6/1/2013


H th Filt W k

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How the Filter Works

A large capacitor is connectedacross the load resistor. This

capacitor filters the pulses into amore constant DC.

When the diode conducts, thecapacitor charges up to thepeak of the sine wave.

Then when the sine voltage

drops, the charge on thecapacitor remains. Since thecapacitor is large it forms a longtime constant with the loadresistor. The capacitor slowlydischarges into the loadmaintaining a more constant

output. The next positive pulse comes

along recharging the capacitorand the process continues.


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Ripple

The capacitor does a good job of smoothing thepulses from the rectifier into a more constant DC.

A small variation occurs in the DC because thecapacitor discharges a small amount between the

positive and negative pulses. Then it recharges.This variation is called ripple.

The ripple can be reduced further by making thecapacitor larger.

The ripple appears to be a sawtooth shaped ACvariation riding on the DC output.

A small amount of ripple can be tolerated in somecircuits but the lower the better overall.


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Ripple voltage

The output of rectifier circuit is the

pulsating DC voltage .The resulting

pulsating dc signal smooth the output

voltage, we used filter circuit. Figure belowshows the output wave before and after

the filter circuit.


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Ripple voltage


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Types of filter

There are 4 main types of filter:-

i)Filter capacitor

i) Resistor capacitor (RC filter)

ii) Inductance capacitor (LC filter)

iii) type filter


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RC filter diagram


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RC filter

Is an electric circuit composed of resistors

and capacitors driven by voltage or

current source


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Operation of RC filter

When a circuit consists of only a charge

capacitor and a resistor. The capacitor will

discharge its stored energy through the

resistor. The voltage across the capacitorcan be found by kirchoffs current law.

Where the current through the capacitor

must equal the current through theresistor.


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LC filter


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Operation of LC filter

A capacitor stores energy in the electric

fieldbetween its plates, depending on the

voltage across it, and an inductor stores

energy in its magnetic field, depending onthe currentthrough it.

http://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_field

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filter

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Combination C and LC filter

PI-TYPE FILTERS use both capacitive

and inductive filters connected in a pi-type

configuration. Because of the combinationof filtering devices, the ability of the pi filter

to remove ripple voltage is superior to that

of either the capacitance or inductancefilter


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The Regulator

Most regulators are ICs . These are feedback control circuits that

actually monitor the output voltage to detectvariations.

If the output varies, for whatever reason, theregulator circuit automatically adjusts theoutput back to the set value.

Regulators hold the output to the desiredvalue.

Since ripple represents changes in theoutput, the regulator also compensates forthese variations producing a near constant

DC output.


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IC Regulator

The 78xx (also sometimes known as LM78xx) series of devices is afamily of self-contained fixed linear voltage regulator IC. The 78xx

family is a very popular choice for many electronic circuits which

require a regulated power supply, due to:

i. easy of use and

ii. Low cost.


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Voltage regulator circuit

The power supply means the output

changes when the input supply or the load

resistance also changes. The main

purpose of voltage regulator is to decreasethe changes to zero(0) or at least to the

minima value.


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There are three (3) voltage regulator

circuit normally used :-

a. Zener diode voltage regulator

b. Series transistor voltage regulator

c. Integrated circuits voltage regulator

(LM7805)


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Zener diode voltage regulator


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Series transistor voltage regulator


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Operation

Connect the transistor serial with load and

it will control the input voltage value to

output.If the output voltage decreases ,the

increases VBE will cause the transistor toproduce more current value will make the

output voltage increases and make the

output voltage constant.


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Operation

Zener diode as a refer voltage .It is same

process if the output voltage increases.

Transistor will decrease the current value ,

cause the output voltage decrease and theoutput voltage become constant.


Integrated circuits voltage regulator

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g g g

(LM7805)


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Operation

The serial LM 78XX(where XX=

05,06,08,10,12,15,18 or 24).It is 3

terminal voltage regulator .IC LM 7805 will

produce the output voltage +5V .LM 7806will produce the 6V output voltage. LM

7824 will produce +24V output voltage.


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Voltage divider circuit

In electronic devices system, especially

big or complicated .It is contains several

circuit level, sometime use DC voltage

which are different value. For example TVsystem have more than 10 circuit level

,different function and some of the need

DC voltage,100V,48V,12V and so on.


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POWER SUPPLY CIRCUIT


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Example

Based on figure below, name and explain

briefly circuit in part A dan part B,

If part A is changed to Bridge Rectifier,

re-draw the complete circuit for power

supply unit.


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Example


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Solution


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Solution

The operation :-

When ac voltage supply to the circuit, M and N

at the secondary transformer will become +ve

and ve(exchange).When the circle of inputvoltage in terminal become +ve ,G become a

potential (ground) and N become ve .D1diode

will forward biased while D2will reverse biased.

Current will flow along M, D1, C, A, B, G.A +vecycle wave will produce at the RLload. When the

ve cycle ,input


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Solution

voltage supply ,M terminal becomeve ,Gwill zero potential(grounded) and N

become +ve.D2 diode will forward biased

while D1 will reverse biased. Current willflow along N, D2, C, A, B, G. Current flow

through RLduring the +ve cycle is similar

when ve cycle, we will got the similarshape of wave too.

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Solution

The direction of current flow through RLduring +ve cycle = the direction of current

flow through RLwhenve cycle. When we

connect the oscilloscope across RL, wewill know the shape of the output voltage

is similar


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Solution

Part BZener Diode Voltage Regulator

The operation;-

Zener diode will functions as voltage regulator

when reversed biased.Zener diode has theirown advantages, can be regulate their voltage

when it is operate at the zener region. To

operate, the input voltage must higher than

zener voltage and the load resistance not effectthe zener diode is zero


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Solution


THE END

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THE END

chapter 1 ee 301

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