POWER ELECTRONICS PART TWO

1. Dynamic equalizing circuit is used for
1. equal division of voltage across each thyristor in parallel.
2. equal division of current through each thyristor in series.
3. equal division of voltage across each thyristor.
4. equal division of current through each thyristor in parallel.

2. 4 thyristors rated 200 V in series. The operating voltage of the string is 600 V. Derating factor of the string is
1. 0.25.
2. 0.75.
3. 0.2.
4. 0.7.

3. A
string of n parallel SCRs is operated at 72 KA, the rating of each SCR
is 1 KA. If derating factor of the string is 0.1. Then calculate the
value of n

1. 70.
2. 90.
3. 80.
4. 60.

4. For series connected SCR a dynamic equalising circuit consists of
1. series R and diode with C across R.
2. R and C in series but with diode across C.
3. series R and diode with C across R.
4. R and C in series but with diode across R

5. Anode current in an SCR consists of
1. Both electron and holes.
2. either electron or holes.
3. electrons only.
4. holes only.

6. Dynamic equalising circuit is useful
1. to limit di / dt of SCR.
2. both to limit dV / dt of SCR & for voltage equalisation
3. to limit dV / dt of SCR.
4. for voltage equalisation

7. Which following is a two terminal three layer device?
1. None of these.
2. MOSFET.
3. BJT.
4. Power dioed.

8. Which of following is not a power transistor?
1. SITS.
2. TRIAC.
3. IGBTs.
4. COOLMOS.

9. Which of following is normally ON device
1. SIT.
2. TRIAC.
3. IGBT.
4. BJT.

10. Power transistor are type of
1. MOSFETs.
2. BJTs.
3. All of these
4. IGBTs.

11. Which of the following is true?
1. SIT is a high power, high voltage device.
2. SIT is a low power, high frequency device.
3. SIT is a high power, low frequency device.
4. SIT is a high power, high frequency device.

12. A GTO can be turned on by applying
1. Positive gate signal.
2. Positive drain signal.
3. None of these.
4. Positive source signal.

13. SITH is also known as
1. Filled controlled rectifier.
2. Silicon controlled rectifier.
3. Filled controlled diode.
4. None of these.

14. The
reverse recovery time of diode is trr = 3 sec and the rate off all of
the diode current is di/dt = 30 A/Sec. The storage charge current QRR is

1. 130 A
2. 135 A
3. 140 A
4. 145 A

15. A power MOSFET has three terminals called
1. Drain, source and base.
2. Collector, emitter and base.
3. Collector, emitter and gate.
4. Drain, source and gate.

16. A modern power semiconductor device that combines the characteristic of BJT and MOSFET is
1. GTO
2. IGBT.
3. FCT.
4. MCT.

17. Thermal voltage VT can be given by
1. KT/q.
2. (K²/q)(T + 1/T – 1).
3. qT/K.
4. Kq/T.

18. IGBT combines the advantages of
1. BJTs and SITs.
2. SITs and MOSFETs.
3. BJTs and MOSFETs.
4. None of these.

19. COOLMOS device can be used in application up to power range of
1. 100 KVA.
2. 2 KVA.
3. 500 VA.
4. 1 KVA.

20. Compared to transistor, ______________ have lower on state conduction losses and higher power handling capability
1. Thyristor
2. Semi conductor diodes.
3. MOSFETs.
4. TRIACs.

21. A thyristor can termed as
1. Square wave switch.
2. AC switch.
3. all of these
4. DC switch.

22. Thyristor is nothing but a
1. Amplifier with higher gain.
2. Amplifier with large current gain.
3. Controlled switch.
4. Controlled transistor.

23. BCT is used for
1. High power current control.
2. Low power current control.
3. High power phase control.
4. Low power phase control.

24. Which of following devices has highest di/dt and dv/dt capability?
1. SITH.
2. SIT.
3. SCR.
4. GTO.

25. Which of the following is disadvantage of fast recovery diodes?
1. Doping is carried out.
2. Recovery is only 50 µs.
3. Recovery is only 5 µs.
4. None of these.

26. A power semiconductor may undergo damage due to
1. High dv/dt.
2. High di/dt.
3. Low dv/dt.
4. Low di/dt.

27. If the anode current is 800 A, then the amount of current required to turn off the GTO is about
1. 400 A.
2. 600 A.
3. 200 A.
4. 20 A.

28. Which semiconductor device acts like a diode and two transistor?
1. SCR.
2. UJT.
3. Triac.
4. Diac.

29. The latching current of GTO should be of order
1. 500 mA.
2. 2 A.
3. 100 mA.
4. 1 A.

30. The maximum di/dt in a SCR is
1. Directly proportional to supply voltage.
2. none of these
3. Directly proportional to inductance in the circuit.
4. both

31. Switching frequency of SITH is
1. 60 KHz.
2. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of
3. 5 KHz.
4. 10 KHz.
5. 100 KHz.

32. A single phase full bridge inverter can operate in load commutation mode in case load consists of
1. RLC overdamped.
2. RLC critically damped.
3. RL.
4. RLC underdamped.

33. The function of snubber circuit connected across the SCR is to
1. suppress dV / dt.
2. decrease di / dt.
3. increase dV / dt.
4. decrease dV / dt.