Power semiconductors

Learn the basics of power semiconductors — the strengths of SiC and GaN, IGBT operation and the two-dimensional electron gas in GaN HEMTs — through multiple-choice questions.

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Power semiconductors: key points

Power semiconductors convert and control electric power and are used in inverters, power supplies, electric vehicles and more. They need high breakdown voltage, low on-resistance and fast switching.

In addition to silicon MOSFETs and IGBTs, devices made from SiC and GaN, which have large band gaps and high breakdown fields, are becoming widespread. It is important to understand how material properties relate to device structure.

All Power semiconductors questions (50)

  1. What is the main reason SiC (silicon carbide) is advantageous over Si for high-voltage power devices?
  2. Which correctly describes an IGBT?
  3. Which is the channel through which current flows in a GaN HEMT?
  4. Which correctly describes the relationship between breakdown voltage and on-resistance in silicon power MOSFETs?
  5. What is the main role of an inverter in power electronics?
  6. In power devices, which loss mainly increases when the switching frequency is raised?
  7. Which is a characteristic of a superjunction (SJ) MOSFET?
  8. If a power device with a thermal resistance of 2 °C/W dissipates 10 W, what is the temperature rise?
  9. What is the parasitic diode that forms structurally inside a power MOSFET called?
  10. What is the general term for semiconductors with a larger band gap than silicon, such as SiC and GaN?
  11. What is the main role of a gate driver for power semiconductors?
  12. Why are power devices required to be 'normally off', with no current flowing at 0 V gate voltage?
  13. What is the main advantage of using SiC Schottky barrier diodes as freewheeling diodes in inverters and similar circuits?
  14. Which is a characteristic of a thyristor?
  15. In high-power modules, what is the main purpose of the insulating substrate (such as a ceramic substrate) placed under the power chips?
  16. When SiC or GaN power devices switch at high speed, which problem particularly needs countermeasures?
  17. If the current in a wire with a parasitic inductance of 10 nH changes by 10 A in 10 ns, approximately what voltage is induced?
  18. What is the purpose of a power factor correction (PFC) circuit used in power supplies?
  19. What is the main advantage of using SiC power devices in electric vehicle inverters?
  20. In an ideal step-down chopper (buck converter) with an input voltage of 12 V and a switch duty cycle of 0.25, what is the output voltage?
  21. Which DC-DC converter outputs a DC voltage higher than its input?
  22. At IGBT turn-off, what is the phenomenon called in which the current does not drop to zero immediately but trails off because of stored minority carriers?
  23. Which is a known challenge of SiC MOSFETs?
  24. In SiC power modules operating at high temperatures, which material is sometimes used instead of solder to bond the chips?
  25. What is the main advantage of raising the switching frequency of a power converter?
  26. In a power device gate drive circuit, what is the effect of increasing the gate resistance?
  27. Which metric indicates how long a power device can withstand a short circuit, such as both upper and lower switches of an inverter turning on at once, without being destroyed?
  28. What is the purpose of providing a short period in which both switches are off (dead time) when switching the upper and lower switches of an inverter?
  29. Which is a known cause of degradation when current flows continuously through the body diode of a SiC MOSFET?
  30. Which is an example of an everyday product in which GaN power devices are increasingly used?
  31. What is the main role of power semiconductors?
  32. What is the conduction loss of a power MOSFET with an on-resistance of 10 mΩ carrying 10 A?
  33. What is the main purpose of attaching a heat sink to a power device?
  34. How many switching devices does a typical three-phase inverter for driving a three-phase motor use?
  35. In power circuits and the like, what is the small resistor placed in series in the current path to measure current called?
  36. Why is a switching power supply more efficient than a linear power supply, which operates its transistor linearly?
  37. What is the main advantage of the trench gate structure in power MOSFETs, in which the gate is buried in a groove etched into the silicon?
  38. Which correctly describes the typical division of use between silicon MOSFETs and IGBTs?
  39. What is the main purpose of a snubber circuit in a power device switching circuit?
  40. When one switch of an inverter turns on, which loss increases due to the reverse recovery of the diode in the opposite arm?
  41. Among soft-switching techniques for power converters, which correctly describes ZVS (zero-voltage switching)?
  42. When a power MOSFET's gate is charged with a constant current, why does the gate voltage stay flat for a while (the Miller plateau)?
  43. Why is a negative gate voltage (for example, −3 to −5 V) sometimes applied to SiC MOSFETs or IGBTs in the off state?
  44. What maximum junction temperature (Tj max) is commonly specified for typical silicon power devices?
  45. When choosing power devices, why are devices with a voltage rating higher than the actual operating voltage used (derating)?
  46. When does the avalanche ruggedness of a power MOSFET become important?
  47. What is a typical failure seen in power cycling tests, which repeatedly heat and cool power modules?
  48. In packages for fast-switching power devices, what is the purpose of a dedicated source terminal for the gate-drive return (Kelvin source)?
  49. Which circuit uses a diode and capacitor to create a gate voltage above the supply to drive the upper (high-side) n-channel MOSFET of a half bridge?
  50. In Baliga's figure of merit, used to compare materials for unipolar power devices, which material property has a particularly strong effect?

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