MCQ in Power Electronics Part 1 | ECE Board Exam

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 In a flyback converter, the inductor of the buck-boost converter has been replaced by a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

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

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

4. A step – down choppers can be used in

A. Electric traction

B. Electric vehicles

C. Machine tools

D. All of these

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

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

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

A. C_min = V / ( Vr L f2 )

B. C_min = ( 1 – D ) V / ( Vr L f2 )

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

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

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

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

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

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

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

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

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

A. One

B. Three

C. Six

D. Nine

15. Unipolar modulation is generally used in

A. AC – AC converters

B. AC – DC converters

C. DC – AC converters

D. DC – DC converters

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

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

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

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

20. A full wave rectifier with resistive load produces

A. Second harmonic

B. Third harmonic

C. Fifth harmonic

D. Do not produce harmonics

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

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

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

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

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

A. rectifier

B. inverter

C. chopper

D. regulator

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

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

A. True

B. False

C. none

D. all

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

A. True

B. False

C. none

D. all

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

A. 8D×V_in

B. 5D×V_in

C. 2D×V_in

D. D×V_in

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

A. D×V_in

B. V_in ÷ (1-D)

C. D×V_in ÷ (1-D)

D. None of these

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

A. 8D×V_in

B. 5D×V_in

C. 2D×V_in

D. D×V_in

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

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

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

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

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

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

38. A fully controlled converter uses

A. diodes only

B. thyristors only

C. both diodes and thyristors

D. none of the mentioned

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

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

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

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

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

D. load current, load voltage

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

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

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

A. power generation

B. electric heating

C. conveyor belt motion

D. power transmission

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

48. IGT stands for

A. Insulated gate bipolar transistor

B. Insulated gate bidirectional transistor

C. Inductive gate bipolar transistor

D. Inductive gate bidirectional transistor

49. Number of PN junction in an SCR is

A. Two

B. Three

C. Four

D. Five

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

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