flyback converters v4

Development of SiC-Based PEBB 1000

May 1, 2023

PWM DC-DC Flyback Converters

Pedro Campos FernandesJun Wang

May 1, 2023 Development of SiC-Based PEBB 1000 2

1. One-Switch Flyback Converter

Advantages Simplicity: fewer semiconductor and magnetic components Low cost

Disadvantages Resonance caused by the leakage inductance and the device junction capacitances

High-frequency ringing and EMI


2. Ideal One-Switch Flyback Converter

Circuit components:

Q: Ideal MOSFET Switch D: Ideal Rectifier Diode C: Output Capacitance RL: Load Resistance Vin: Input Voltage Source I1: Input Current (primary) LM: Magnetizing Inductance IM: Magnetizing Current I2: Diode Current (secondary) T: Ideal Flyback Transformer


2. Ideal One-Switch Flyback Converter Simulation model:

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2.1. CCM Operation2.1.1. First Stage: DTS

Q is ON D is OFF Energy from the DC sourceis stored in LM



2.1. CCM Operation2.1.2. Second Stage: (1-D)TS

Q is OFF D is ON Transformer voltage reversesforward-biasing the rectifier diodeand delivering energy to the output


3. Non-Ideal One-Switch Flyback Converter

Circuit components:

Q: MOSFET Switch D: Rectifier Diode C: Output Capacitance RL: Load Resistance Vin: Input Voltage Source I1: Input Current (primary) LM: Magnetizing Inductance IM: Magnetizing Current I2: Diode Current (secondary) T: Flyback Transformer CJ: Diode Junction Capacitance CDS: Drain-Source Capacitance Lleak: Leakage Inductance


3. Non-Ideal One-Switch Flyback Converter Simulation model:

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Subinterval 1: Q is switching from OFF to ON D is switching from ON to OFF Switch transient ringing


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Subinterval 2: Q is effectively ON D is effectively OFF No switch transient ringing


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Subinterval 3: Q is switching from ON to OFF D is switching from OFF to ON Switch transient ringing


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Subinterval 4: Q is effectively OFF D is effectively ON No switch transient ringing



3.2. Ideal Case vs. Parasitic Case


4. Two-Switch Flyback Converter

Advantages Maximum switch voltage is clamped to the DC input voltage Vin Leakage inductance energy is also clamped and recycled back to the DC

input source (improve efficiency) Reduced switching and conduction losses


5. Non-Ideal Two-Switch Flyback Converter

Circuit components: Q1,2: Symmetrical MOSFET Switches D1,2: Symmetrical Clamping Diodes D: Rectifier Diode C: Output Capacitance RL: Load Resistance Vin: Input Voltage Source I1: Input Current (primary) LM: Magnetizing Inductance IM: Magnetizing Current I2: Diode Current (secondary) T: Flyback Transformer CJ: Diode Junction Capacitance CDS1,2: Drain-Source Capacitances Lleak: Leakage Inductance


5. Non-Ideal Two-Switch Flyback Converter Simulation model:

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Subinterval 1: Q1, Q2 are switching from OFF to ON D is switching from ON to OFF D1, D2 are OFF Switch transient ringing


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Subinterval 2: Q1, Q2 are effectively ON D is effectively OFF D1, D2 are OFF No transient ringing


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Subinterval 3: Q1, Q2 are switching from ON to OFF D is switching from OFF to ON D1, D2 are OFF Voltage spike


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Subinterval 4: Q1, Q2 are switching from ON to OFF D is effectively ON D1, D2 are ON Switch voltages VDS1, VDS2 are clamped to Vin


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Subinterval 5: Q1, Q2 are switching from ON to OFF D is ON D1, D2 are switching from ON to OFF Switch transient ringing


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Subinterval 6 Q1, Q2 are effectively OFF D is ON D1, D2 are effectively OFF No transient ringing



5.2. One-Switch vs. Two-Switch


5.2. One-Switch x Two-Switch


5.3. Component Mismatches

Real applications do not provide perfect symmetry between junction capacitances and gate driver signals

There are mismatches between these variables and they lead to different behaviors during the converter operation



Two types of mismatch will be covered:

20% mismatch on drain-source capacitance of the low side MOSFET switch Q2 given the high side MOSFET switch Q1 as reference

5% delay (given the period as reference) on the gate driver of the low side MOSFET switch Q2


5.3. Component Mismatches5.3.1. Capacitance Mismatch CDS1 = 120 pF and CDS2 = 144 pF

Q1 is clamped earlier than Q2, i.e.,D1 starts conducting earlier than D2 Q1, Q2 voltages reach different steady values after the ringing dies


5.3. Component Mismatches5.3.2. Gate Drive Delay Mismatch DelayQ1 = 0 s and DelayQ2 = 0.17 us

Q2 turns ON later, so Q1 will be clamped earlier Q1 turns ON earlier, leading to another clamping action during the delayed turn ONof Q2


5.3. Component Mismatches5.3.3. Merged Mismatch



Possible Solutions

Design an integrated solution with complete control circuit and gate drive for both high side (Q1) and low side (Q2) switches

Work with safety margins so that the circuit can still present good performance for a certain percentage of mismatch


6. Power Losses on Flyback Converters

Design considerations: Zero winding resistances (rprimary = rsecondary = 0) Zero leakage resistance The MOSFET switches and clamping diodes are considered

symmetrical to each other Two-Switch topology - switches model: IRF510

100 V, 5 A, ron,max = 0.85 Ω and CDS = 60 pF One-Switch topology - switch model: IRF840

500 V, 8 A, ron,max = 0.54 Ω and CDS = 120 pF Rectifier Diode model: MBR10100 100 V, 10 A, VF = 0.65 V and rF = 20 mΩ with CJ = 200 pF Clamping Diodes model: MBR10100

100 V, 10 A, VF = 0.65 V and rF = 20 mΩ with CJ = 0 F


6. Power Losses on Flyback Converters

Losses presented by the design:

Conduction Losses

Forward Voltage Losses

Switching Losses


6.1. Conduction Losses6.1.1. MOSFET Switches Q1, Q2 Since Q1, Q2 are symmetrical to each other, conduction losses will be given by:

6.1.2. Rectifier Diode D3

6.1.3. Clamping Diodes D1, D2 Since Q1, Q2 are symmetrical to each other, conduction losses will be given by:

And


6.2. Forward Voltage Losses6.2.1. Rectifier Diode D3 The average power dissipated by the forward voltage across the ON stage rectifier

diode is given by:

6.2.2. Clamping Diodes D1, D2 The average power dissipated by the forward voltage across the ON stage

clamping diodes is given by:

And


6.3. Switching Losses

Switching Losses on the MOSFET switches can be obtained by the simplified formulation presented on [4]:

And


6.4. Total Power Loss

The total power loss of the circuit is given by:

With


6.5. Results

Initial Considerations

The simulation time covered 0 to 0.05s

The samples were saved on a .mat file and a reused on a MATLAB script in order to compute the losses

The RMS and average currents were computed considering one switching cycle only at steady state


6.5. Results

Condcution Losses Forward Voltage Losses

Switching Losses Total Losses Efficiency0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10.

064

0.35

3 0.43

3

0.84

9

0.87

4

0.07

4

0.35

5

0.04

2

0.47

0

0.92

4

Power Losses at CCM (W)

One-Switch Two-Switch


6.5. Results

Comparison of the performance of the converters in CCM:

The conduction losses slightly increased due to the presence of more components on the two-switch topology

The switching losses were drastically reduced

The efficiency increased 5 %


6.5. Results

Conduction Losses Forward Voltage Losses Switching Losses Total Losses Efficency 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10.

064

0.35

3

0.43

3

0.84

9

0.87

4

0.08

4

0.36

7

0.14

0

0.59

2

0.91

2

0.07

4

0.35

5

0.04

2

0.47

0

0.92

4

0.10

2

0.36

5

0.01

1

0.47

7

0.92

7

Power Losses at CCM and BCM (W)

One-Switch CCM One-Switch BCM Two-Switch CCM Two-Switch BCM


6.5. Results

Comparison of the performance of the converters in CCM vs. BCM:

Higher conduction losses at BCM

Lower switching losses for both topologies at BCM

Higher efficiency for both topologies at BCM


7. Conclusion

Does the Two-Switch Flyback Converter present a better performance when compared to the One-Switch topology?

Voltage across the MOSFET switches is clamped to Vin (no high-voltage spikes)

Lower ringing effect

Lower switching losses

Higher efficiency


8. References

[1] “Improving the Performance of Traditional Flyback-Topology With Two-Switch –Approach”, J. Pesonen; Texas Instruments

[2] “Understand Two-Switch Forward/Flyback Converters”, Y. Xi, R. Bell; National Semiconductor

[3] “Hard-Switching and Soft-Switching Two-Switch Flyback PWM DC-DC Converters and Winding Loss due to Harmonics in High-Frequency Transformers”, D. M. Bellur, Wright State University

[4] “Two-Switch Flyback PWM DC-DC Converter in Continuous-Conduction Mode”, D. M. Bellur, M. K. Kazimierczuk, Wright State University

[5] “Fundamentals of Power Electronics”, R. W. Erickson, D. Maksimovic, University of Colorado Boulder

[6] “Characterization and Modeling of High-Switching-Speed Behavior of SiC Active Devices”, Zheng Chen; Virginia Polytechnic Institute and State University

[7] “AN-9010 MOSFET Basics”, Fairchild Semiconductor

[8] “Analysis of SiC MOSFETs under Hard and Soft-Switching”, M. R. Ahmed, R. Todd, A. J. Forsyth, The University of Manchester, UK

[9] “Power Electronics - A First Course”, N. Mohan, University of Minnesota

[10] “Development of an Isolated Flyback Converter Employing Boundary-Mode Operation and Magnetic Flux Sensing Feedback”, M. V. Kenia, Massachusetts Institute of Technology

flyback converters v4

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