Power Electronics MCQs Quiz Multiple Choice Questions & Answers

1. A crowbar is a circuit which is used to protect a

1. current sensitive load from excessive ac power supply output voltages
2. current sensitive load from excessive dc power supply output voltages
3. voltage sensitive load from excessive ac power supply output voltages
4. voltage sensitive load from excessive dc power supply output voltages

2. A diac has........................terminals

1. None of the above
2. Three
3. Four
4. Two

3. A diac has....................pn junctions

1. None of the above
2. Two
3. Three
4. Four

4. A diac has ................... semiconductor layers

1. None of the above
2. Two
3. Four
4. Three

5. A diac is simply.....................

1. None of the above
2. A three junction device
3. A triac without gate terminal
4. A single junction device

6. A diac is turned on by ...................

1. None of the above
2. Gate voltage
3. Gate current
4. A breakover voltage

7. A full wave rectifier with resistive load produces

1. Do not produce harmonics
2. Third harmonic
3. Fifth harmonic
4. Second harmonic

8. A triac can pass a portion of ..................... half-cycle through the load

1. None of the above
2. Only negative
3. Both positive and negative
4. Only positive

9. A triac has .................... semiconductor layers

1. Five
2. Three
3. Four
4. Two

10. A Triac has three terminals viz.....................

1. None of the above
2. Two main terminal and a gate terminal
3. Cathode, anode, gate
4. Drain, source, gate

11. A triac is a ................ switch

1. None of the above
2. Unidirectional
3. Mechanical
4. Bidirectional

12. A triac is equivalent to two SCRs .......................

1. None of the above
2. In series
3. In inverse-parallel
4. In parallel

13. A UJT has ....................

1. None of the above
2. One pn junction
3. Three pn junctions
4. Two pn junctions

14. A UJT is sometimes called................ diode

1. Double-base
2. High resistance
3. Single-base
4. Low resistance

15. AC power in a load can be controlled by using

1. four SCRs in series
2. two SCRs in series
3. three SCRs in series
4. two SCRs in parallel opposition

16. After peak point, the UJT operates in the ................... region

1. None of the above
2. Saturation
3. Negative resistance
4. Cut-off

17. An SCR can be used

1. all of these
2. for power control
3. for speed control of dc shunt motor
4. as static conductor

18. An SCR is made up of silicon because

1. silicon has large leakage voltage than germanium
2. silicon has small leakage current than germanium
3. silicon has small leakage voltage than germanium
4. silicon has large leakage current than germanium

19. Between the incoming and outgoing devices in voltage commutation

1. None of these
2. Small overlapping operation
3. No overlapping operation
4. Large overlapping takes place

20. Between the peak point and the valley point of UJT emitter characteristics we have ....................... region

1. None of the above
2. Negative resistance
3. Cut-off
4. Saturation

21. Double fourier series analysis of PWM is

1. All of these
2. Three dimensional functions
3. One dimensional functions
4. Two dimensional functions

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

1. Independent on both the load current and load voltage
2. Dependent on the voltage
3. Dependent on both the load current and load voltage behind the short circuit current
4. Dependent on the load current

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

1. A low on - resistance switch can be added in series
2. A low on - resistance switch can be added in parallel
3. A high on - resistance switch can be added in series
4. A high on - resistance switch can be added in parallel

24. For bidirectional operation of converters

1. A series combination of controllable switch and a capacitor is used
2. A parallel combination of controllable switch and capacitor is used
3. A series combination of controllable switch and a diode is used
4. A parallel combination of controllable switch and a diode is used

25. For similar carrier and modulating signals, the line current used in CSI is

1. Identical to phase voltage in CSI
2. Identical to line current in VSI
3. Identical to phase voltage in VSI
4. Identical to line voltage in a VSI

26. For sweptfrequency measurements, the input impedance of the mismatched transmission line would vary with frequency as the electrical length ofthe transmission line would

1. Either (a or b)
2. Remains same with change in frequency
3. Increase with frequency
4. Decrease with frequency

27. Harmonics in 3 phase inverters can be reduced by using

1. None of these
2. Active filter
3. Both passive and active filters
4. Passive filter

28. In a 3 phaseCSI, if the required line output voltages are balanced and 120 degreeout of phase, then the chopping angles are used to eliminate only theharmonics at frequencies

1. All of these
2. 7
3. 11
4. 5

29. In a load commutated DC - DC chopper, the capacitor has a

1. Symmetric sinusoidal voltage across itself
2. Symmetric rectangular voltage across itself
3. Symmetric trapezoidal voltage across itself
4. Symmetric triangular voltage across itself

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

1. Nine
2. Three
3. Six
4. One

31. In a UJT, the p-type emitter is ........................ doped

1. None of the above
2. Heavily
3. Moderately
4. Lightly

32. In bipolar modulation, the carrier is symmetric about zero with amplitude equal to Cm, the PWM output

1. Switches between 0 and +1
2. Switches between -1 / 2 and +1 / 2
3. Switches between -1 and +1
4. Zero

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

1. None of these
2. The capacitance voltage adds to the supply voltage
3. Both (a and b)
4. Voltage across the commutating inductances collapses

34. In EMCsignal, the source delivers maximum power to the input of transmissionline when the transmission line input impedance

1. None of these
2. Greater than the source resistance
3. Smaller than the source resistance
4. Is equal to the source resistance

35. In radiative coupling, the emitter radiation field

1. Decays as 2R, where R is the separation distance between the emitter and the receptor
2. Decays as R, where R is the separation distance between the emitter and the receptor
3. Decays as 1 / 2 R, where R is the separation distance between the emitter and the receptor
4. Decays as 1 / R, where R is the separation distance between the emitter and the receptor

36. In single phase VSI, the harmonic which is not present is

1. 7th
2. 3rd
3. 5th
4. 2nd

37. LISN is a device used to measure conducted emissions. LISN stands for

1. Laser integrated stabilization networking
2. Line impedance stabilization network
3. Line integrated stored network
4. Line integrated stabilization network

38. Power electronics essentially deals with control of a.c. power at .....................

1. 50 Hz frequency
2. Frequencies above 1000 kHz
3. Frequencies less than 10 Hz
4. Frequencies above 20 kHz

39. Silicon controlled rectifier can be turned on

1. By making current non zero and turned off by making current zero
2. And turned off by applying gate pulse
3. By applying a gate pulse and turned off by removing the gate pulse
4. By applying a gate pulse and turned off only when current becomes zero

40. Single phase VSI are mainly used in

1. All of these
2. Ups
3. Multilevel configuration
4. Power supplies

41. The advantage of using free - wheeling diode in half controlled bridge converter is that

1. There is always a path for the ac current independent of the ac line
2. There is always a path for the ac current independent of the ac line
3. There is always a path for the dc current dependent of the ac line
4. There is always a path for the dc current independent of the ac line

42. The conduction losses in IGBT is

1. Equal to that of BJT
2. Lower than that of MOSFET
3. Equal to that of MOSFET
4. More than that of MOSFET

43. The device that does not have the gate terminal is ............................

1. Diac
2. FET
3. SCR
4. Triac

44. The device that exhibits negative resistance region is .........................

1. UJT
2. Triac
3. Transistor
4. Diac

45. The effects of EMI can be reduced by

1. All of these
2. Reducing the efficiency of the coupling path
3. Reducing the susceptibility of the receptor
4. Suppressing emissions

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

1. Trapezoidal wave
2. Square wave
3. Saw - tooth wave
4. Sine wave

47. The most suited gate pulses given to the AC regulator with R - L load can be in the form of

1. None of these
2. Large isolating pulse transformer
3. A train of pulses
4. Continuous signal

48. The normal way to turn on a diac is by ...........................

1. None of the above
2. Gate voltage
3. Breakover voltage
4. Gate current

49. The output power of the cascaded amplifier-attenuator system can be determined using

1. Actual gain of attenuator
2. Actual gain of amplifier and attenuator
3. Gain in dB of amplifier and attenuator
4. Actual gain of amplifier

50. The power MOSFET device is a

1. Voltage controlled bipolar device
2. Voltage controlled unipolar device
3. Current controlled bipolar device
4. Current controlled unipolar device