Power electronics MCQ #8

1) IGBT is a modern power semiconductor device, that combine the characteristics of

      (a) SCR and MOSFET.

      (b) MOSFET and BJT.

      (c) BJT and SCR.

      (d) GTO and Thyristor.

2) Which of the following power electronic device can be used for high frequency switching application?

      (a) Schottky diode.

      (b) Microwave transistor.

      (c) BJT.

      (d) Power MOSFET.

3) Turn on and turn off times of transistor depends on

      (a) junction capacitance.

      (b) current gain.

      (c) applied voltage.

      (d) applied frequency.

4) A semiconductor device which act like a diode and two transistors is

      (a) TRIAC.

      (b) DIAC.

      (c) MOSFET.

      (d) UJT.

ANSWER: | 1-b | 2-d | 3-a | 4-d |

5) UJT is known as

      (a) voltage-controlled device.

      (b) triggered device.

      (c) relaxation oscillator.

      (d) current controlled device.

6) During forward blocking state, the SCR has

      (a) Low current, medium voltage

      (b) Large current, low voltage

      (c) Medium current, large voltage

      (d) Low current, large voltage

7) In class A and class B commutation the resonating circuit has to be

      (a) Over damped

      (b) Negatively damped

      (c) Under damped

      (d) Critically damped

8) A cycloconverter is a frequency changer from

      (a) lower to higher frequency with one-stage conversion

      (b) higher to lower frequency with two-stage conversion

      (c) higher to lower frequency with one-state conversion

      (d) Either a or c

ANSWER: | 5-a | 6-d | 7-c | 8-d |

9) The latching current of a SCR is 18mA. Its holding current will be

      (a) 6mA

      (b) 12mA

      (c) 18mA

      (d) 54mA

10) Two thyristors of same rating and same specifications

      (a) may have equal or unequal turn on and turn off periods

      (b) will have unequal turn on and turn off periods

      (c) will have equal turn on and turn off periods

      (d) will have equal turn on but unequal turn off periods

11) A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. Find the maximum allowable internal power dissipation if the thermal resistance is 1.6° C/W,

      (a) 20 W

      (b) 50 W

      (c) 92 W

      (d) 128 W

12) In a step-down chopper using pulse width modulation, Ton = 3x10-3 sec. and Toff = 1x10-3 sec. The chopping frequency is

      (a) 333.33

      (b) 250

      (c) 500

      (d) 1000

ANSWER: | 9-a | 10-a | 11-b | 12-b |

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