Power Electronics
Topics for the oral exam
Academic Year 2021/22
Power semiconductor switches, drive and protection circuits
Schottky barrier diode. Reverse blocking.
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Schottky barrier diode: forward conduction. The "limit of silicon" in unipolar conduction.
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P-i-n diodes: reverse blocking. NPT design.
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P-i-n diodes: forward conduction. Conductivity modulation. Forward voltage drop.
Switching characteristics of p-i-n diodes. Reverse recovery: recovery softness factor.
On-state resistance: comparison between unipolar and bipolar conduction.
Power MOSFET transistors: device structures, I-V characteristics, on-resistance.
Power MOSFETs: trade-off between on-resistance and breakdown voltage.
Power MOSFETs: absolute maximum ratings.
10. Power MOSFETs: impact of parasitic capacitances on switching characteristics.
11. Gate charge curve: calculation of switching times and losses.
12. High-side switch drivers: bootstrap.
13. Power MOSFETs: UIS. Overvoltage protection circuits.
14. Power MOSFETs: current-sense strategies, overcurrent protection circuits.
Switch-mode DC-DC converters
15. SM DC-DC converters: CCM vs. DCM operation mode. DC voltage transfer function.
16. SM DC-DC converters: effect of parasitic components on the DC voltage transfer function. Efficiency.
17. SM DC-DC converters: modulation techniques, pulse-width modulator.
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18. Dynamic modeling of non-isolated DC–DC converters under CCM operation.
19. PWM switch: average and small signal model.
20. Small signal model of the pulse-width modulator. Sampling effect.
21. Control-to-output transfer function: effect of a RHP zero.
22. Voltage control mode: key design guidelines for the control loop. Loop shaping.
23. Type I, type II and type III compensators. Compensator design techniques.
24. k-factor design method.
25. CCM boost converter: compensation; RHPZ bandwidth limitation.
26. Feedforward control of switching regulators.
27. Current-mode control: principle of operation, slope compensation.
28. Buck converter: key guidelines for filter inductor selection.
29. Filter inductor: core selection procedure; area product.
30. Filter inductor: gapped vs. distributed magnetic cores.
31. Filter inductor: high-frequency copper losses; proximity effects.
32. Buck converter: selection of the input and output filter capacitors.
33. Soft-start circuits.
34. Flyback converter: CCM vs DCM operation.
35. Flyback converter: transformer design for DCM operation.
36. Flyback converter: impact of leakage inductance; winding interleaving.
Thermal management
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37. Packaging of power devices. Junction-to-case thermal resistance. Power dissipation and continuous current ratings.
Derating.
38. Steady-state heat transfer: guidelines for the design and selection of heat sinks.
39. Transient operation: thermal impedance. Thermal RC model: Foster and Cauer networks.
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40. Transient thermal analysis: single pulse and periodic pulses.