# MCQ in Power Electronics Part 1 | ECE Board Exam

(Last Updated On: August 10, 2022) This is the Multiple Choice Questions Part 1 of the Series in Power Electronics as one of the Electronics Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electronics Engineering field, Electronics Books, Journals and other Electronics References.

#### Start Practice Exam Test Questions Part 1 of the Series

Choose the letter of the best answer in each questions.

1. In a flyback converter, the inductor of the buck-boost converter has been replaced by a

A. Flyback capacitor

B. Flyback resistor

C. Flyback transformer

D. Flyback transistor

Solution:

2. For bidirectional operation of converters

A. A parallel combination of controllable switch and a diode is used

B. A parallel combination of controllable switch and capacitor is used

C. A series combination of controllable switch and a diode is used

D. A series combination of controllable switch and a capacitor is used

Solution:

3. For a buck converter to reduce the conduction losses in diode

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

B. A low on – resistance switch can be added in parallel

C. A high on – resistance switch can be added in series

D. A low on – resistance switch can be added in series

Solution:

4. A step – down choppers can be used in

A. Electric traction

B. Electric vehicles

C. Machine tools

D. All of these

Solution:

5. The output current in PWM DC – DC converter is equal to

A. Average value of the output inductor current

B. Product of an average inductor current and a function of duty ratio

C. Either (a) or (b)

D. None of these

Solution:

6. Advantages of Cuk converter is / are

A. Large number of reactive component

B. Low stress on switch

C. Low stress on capacitor

D. None of these

Solution:

7. In a push – pull converter, the filter capacitor can be obtained as

A. Cmin = V / ( Vr L f2 )

B. Cmin = ( 1 – D ) V / ( Vr L f2 )

C. Cmin = ( 1 – 2 D ) V / 32 ( Vr L f2 )

D. Cmin = ( 1 – 2 D ) V / 42 ( Vr L f2 )

Solution:

8. The control method used for PWM dc – dc converter is

A. Voltage mode control

B. Current mode control

C. Hysteric control

D. All of these

Solution:

9. The control method used for PWM dc – dc converter is

A. Voltage mode control

B. Current mode control

C. Hysteric control

D. All of these

Solution:

10. In current commutated DC-DC choppers, the voltage spike appears across the load when

A. Voltage across the commutating inductances collapses

B. The capacitance voltage adds to the supply voltage

C. Both (a) and (b)

D. None of these

Solution:

11. In a load commutated DC – DC chopper, the capacitor has a

A. Symmetric triangular voltage across itself

B. Symmetric rectangular voltage across itself

C. Symmetric trapezoidal voltage across itself

D. Symmetric sinusoidal voltage across itself

Solution:

12. Voltage commutation circuit can be converted into a current commutation by interchanging the positions of

A. Diode and capacitor

B. Capacitor and SCR

C. Inductor and capacitor

D. Capacitor and load

Solution:

13. During the commutation period in 3 phase converter, overlap time is

A. Dependent on the load current

B. Dependent on the voltage

C. Dependent on both the load current and load voltage behind the short circuit current

D. Independent on both the load current and load voltage

Solution:

14. In a three-phase converter, the number of notches per cycle is

A. One

B. Three

C. Six

D. Nine

Solution:

15. Unipolar modulation is generally used in

A. AC – AC converters

B. AC – DC converters

C. DC – AC converters

D. DC – DC converters

Solution:

16. Very large values of modulation index (greater than 3.24) lead to

A. Square AC output voltage

B. Sine AC output voltage

C. Triangular AC output voltage

D. Trapezoidal AC output voltage

Solution:

17. With increase in firing angle

A. Both harmonic distortion and quality of input current increases

B. Harmonic distortion increases and quality of input current decreases

C. Harmonic distortion decreases and quality of input current increases

D. Both harmonic distortion and quality of input current decreases

Solution:

18. The advantage of using free – wheeling diode in half controlled bridge converter is that

A. There is always a path for the dc current independent of the ac line

B. There is always a path for the ac current independent of the ac line

C. There is always a path for the dc current dependent of the ac line

D. There is always a path for the ac current independent of the ac line

Solution:

19. The input current waveform of a bridge-controlled rectifier when the load is perfectly filtered is

A. Sine wave

B. Square wave

C. Saw – tooth wave

D. Trapezoidal wave

Solution:

20. A full wave rectifier with resistive load produces

A. Second harmonic

B. Third harmonic

C. Fifth harmonic

D. Do not produce harmonics

Solution:

21. If all the SCRs of 3 phase PAC is replaced by diodes, they would be triggered

A. 120 degree after the zero crossing of the corresponding line voltages

B. 60 degree after the zero crossing of the corresponding line voltages

C. 120 degree before the zero crossing of the corresponding line voltages

D. 60 degree before the zero crossing of the corresponding line voltages

Solution:

22. An RC snubber network used in BJT

A. Divert the collector current during turn – off

B. Improves the reverse bias safe operating area

C. Dissipates a fair amount of switching power

D. All of these

Solution:

23. In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes

A. Positive

B. Negative

C. Zero

D. None of these

Solution:

24. In dual converters,

A. Both rectifiers provide positive current to the load

B. Both rectifiers provide negative current to the load

C. One rectifiers provide positive current to the load and the other negative current

D. One rectifier provide positive current to the source and the other negative

Solution:

25. A single phase ac – dc converter is also known as

A. rectifier

B. inverter

C. chopper

D. regulator

Solution:

26. In ac – dc conversion, when the switch is closed then the sum of voltages around the loop is

A. Zero

B. Non zero

C. Equal to the sum of voltage when switch is open

D. Twice of the voltage when switch is open

Solution:

27. Choppers are used to control the DC voltage level.

A. True

B. False

C. none

D. all

Solution:

28. Cuk-converter is better than Buck converter in terms of the output voltage.

A. True

B. False

C. none

D. all

Solution:

29. What is the formula for output voltage for Buck converter?

A. 8D×Vin

B. 5D×Vin

C. 2D×Vin

D. D×Vin

Solution:

30. What is the formula for output voltage for Buck-Boost converter?

A. D×Vin

B. Vin ÷ (1-D)

C. D×Vin ÷ (1-D)

D. None of these

Solution:

31. What is the formula for output voltage for Boost converter?

A. 8D×Vin

B. 5D×Vin

C. 2D×Vin

D. D×Vin

Solution:

32. Buck-Boost acts as Buck converter for duty cycle is equal to _________

A. 0.9

B. 0.7

C. 0.6

D. 0.4

Solution:

33. Buck-Boost acts as Boost converter for duty cycle is equal to _________

A. 0.8

B. 0.1

C. 0.2

D. 0.4

Solution:

34. Inductor and Capacitor in Buck converter are used to ___________

A. Increase the cost

B. Decrease the cost

C. Filter out the harmonics

D. Increase the harmonics

Solution:

35. Calculate the output voltage of the Buck converter if the supply voltage is 789 V and duty cycle value is 0.9.

A. 711.1 V

B. 710.1 V

C. 722.2 V

D. 713.2 V

Solution:

36. Calculate the output voltage of the Boost converter if the supply voltage is 156 V and duty cycle value is 0.4.

A. 260 V

B. 264 V

C. 261 V

D. 268 V

Solution:

37. Under harmonic free load voltages, the 3 phase VSI

A. Does not contains second harmonic

B. Does not contains third harmonic

C. Does not contains fifth harmonic

D. Does not contains seventh harmonic

Solution:

38. A fully controlled converter uses

A. diodes only

B. thyristors only

C. both diodes and thyristors

D. none of the mentioned

Solution:

39. In a B-2 type full controlled bridge converter

A. one SCR conducts at a time

B. two SCRs conduct at a time

C. three SCRs conduct at a time

D. four SCRs conduct at a time

Solution:

40. In a step down chopper, if Vs = 100 V and the chopper is operated at a duty cycle of 75%. Find the output voltage.

A. 100 V

B. 75 V

C. 25 V

D. none of the mentioned

Solution:

41. Find the expression for output voltage for a step-up chopper, assume linear variation of load current and α as the duty cycle.

A. Vs

B. Vs/α

C. Vs/(1-α)

D. Vs/√2

Solution:

42. Find the output voltage for a step-up chopper when it is operated at a duty cycle of 50% and Vs = 240 V.

A. 240 V

B. 480 V

C. 560 V

D. 120 V

Solution:

43. In the method of phase control, the phase relationship between ___ & ___ is controlled by varying the firing angle

A. supply current, supply voltage

B. end of the load current, end of the load voltage

C. start of the load current, start of the load voltage

Solution:

44. In a single-phase half-wave thyristor circuit with R load & Vs=Vm sinωt, the maximum value of the load current can be given by

A. 2Vm/R

B. Vs/R

C. Vm/2

D. Vs/2

Solution:

45. A single-phase half-wave thyristor circuit with R load is triggered at an angle of α = 0°. As such, the maximum value of the average output voltage would be given by Consider Vs = Vm sinωt.

A. Vm

B. 2Vm/π

C. Vm/π

D. Vm/α

Solution:

46. The AC voltage controllers are used in __________ applications.

A. power generation

B. electric heating

C. conveyor belt motion

D. power transmission

Solution:

47. A cycloconverter is a:

A. Frequency changer from higher to lower frequency with one-state conversion

B. Frequency changer from higher to lower frequency with two-stage conversion

C. Frequency changer from lower to higher frequency with one-stage conversion

D. Either a or c

Solution:

48. IGT stands for

A. Insulated gate bipolar transistor

B. Insulated gate bidirectional transistor

C. Inductive gate bipolar transistor

D. Inductive gate bidirectional transistor

Solution:

49. Number of PN junction in an SCR is

A. Two

B. Three

C. Four

D. Five

Solution:

50. In a silicon-controlled rectifier, the load is connected

A. Across anode

B. In series with anode

C. Across cathode

D. In series with cathode

Solution:

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