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power electronics MCQs

Practise focused power electronics questions with marked answers for exam preparation and subject revision.

power electronics Mcqs
1. The average value of the output voltage in a step down dc chopper is given by__________?
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A. V 0 = D V s

B. V 0 = V s

C. V 0 = V s / D

D. V 0 = V s / ( 1 D )

2. The carrier which are commonly used in constant frequency PWM is______________?
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A. Sawtooth carrier

B. All of these

C. Triangle carrier

D. Inverted sawtooth carrier

3. The control method used for PWM dc dc converter is______________?
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A. Hysteric control

B. All of these

C. Voltage mode control

D. Current mode control

4. A rectifier with an external low pass filter is an example of______________?
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A. Direct switch matrix circuits

B. Embedded converters

C. All of these

D. Indirect switch matrix circuits

5. In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure that___________?
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A. Bottom switch of each leg is on at any instant

B. Top switch of each leg is on at any instant

C. None of these

D. Either A. or B.
6. Which semiconductor device acts like a diode and two transistor?
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A. UJT

B. Diac

C. SCR

D. Triac
7. The typical time of rising time lies between______________?
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A. 1 4 s

B. 90 100 s

C. 10 20 s

D. 40 60 s

8. For a buck converter to reduce the conduction losses in diode
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A. A high on resistance switch can be added in series

B. A low on resistance switch can be added in series

C. A high on resistance switch can be added in parallel

D. A low on resistance switch can be added in parallel

9. An SCR is considered to be a semi controlled device because_______?
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A. it can be turned OFF but not ON with a gate pulse.

B. it conducts only during one half cycle of an alternating current wave.

C. it can be turned ON but not OFF with a gate pulse.

D. it can be turned ON only during one half cycle of an AC.

10. How can we protect SCR from thermal conditions _____________?
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A. Using equalizing circuit

B. Use of snubber circuit.

C. Using heat sink.

D. Using CB and fuse.

11. A crowbar is a circuit which is used to protect a_____________?
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A. voltage sensitive load from excessive dc power supply output voltages

B. current sensitive load from excessive dc power supply output voltages

C. voltage sensitive load from excessive ac power supply output voltages

D. current sensitive load from excessive ac power supply output voltages

12. In BJT, the forward biased base emitter junction inject holes from base to emitter, the holes_______?
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A. Do not contribute to the collector current

B. Contribute to the collector current

C. Only (b) and (c)

D. Result in net current flow component into the base

E. Only (a) and (b)
13. The function of snubber circuit connected across the SCR is to___________?
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A. Decrease di / dt.

B. Increase dV / dt.

C. Decrease dV / dt.

D. Suppress dV / dt.
14. An ideal switch is___________?
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A. Does not carry any current in any direction when it is off

B. All of these

C. Carry current in any direction when it is on

D. Lossless

15. If a shunt motor is started with its field winding open then?
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A. It will rotate at dangerously high speed

B. It will rotate at the same speed as that with its field winding closed

C. It will rotate at less speed as that with its field winding closed

D. None of these

16. An SCR has half cycle surge current rating of 3000 A for 50 Hz supply. One cycle surge current will be_____?
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A. 1500 A.

B. 6000 A.

C. 2121.32 A.

D. 4242.64 A.

17. A TRIAC can be turned on with______________?
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A. Either (a) or (b)

B. None of these

C. Negative voltage at the gate terminal

D. Positive voltage at the gate terminal

18. Which of the following is used in heat sink_____________?
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A. Carbon

B. Aluminium

C. Iron

D. ilver

19. The input current waveform of a bridge controlled rectifier when the load is perfectly filtered is___________?
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A. Saw tooth wave

B. Trapezoidal wave

C. Sine wave

D. Square wave
20. Advantages of Cuk converter is / are_____________?
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A. None of these

B. Low stress on switch

C. Low stress on capacitor

D. Large number of reactive component