power electronics Mcqs
51. Which of the following is true about SIT?
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A. SIT is a high power, high frequency device

B. SIT is a low power, high frequency device

C. SIT is a high power, high voltage device

D. SIT is a high power, low frequency device

52. Example of a voltage clamping device______________?
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A. snubber circuit

B. fast acting fuse

C. aluminium block

D. metal oxide varistor
53. What is used to protect the SCR from over current ________________?
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A. Heat sink.

B. CB and fuse.

C. Snubber circuit.

D. Voltage clamping device.

54. SITH is also known as___________?
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A. None of these

B. Filled controlled diode

C. Filled controlled rectifier

D. Silicon controlled rectifier

55. A silicon controlled racitifier (SCR) is a ____________?
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A. Device with three junction

B. Unijunction device

C. Device with four junction

D. None of the above

56. TRIAC is a semiconductor power electronic device which contains____________?
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A. Two SCRs connected in parallel

B. Two BJTs connected in series

C. Two SCRs connected in series

D. Two SCRs connected in reverse parallel
57. In dual converters________________?
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A. Both rectifiers provides 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 current to the load

58. A Triac is a ______________?
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A. 3 terminal bidirectional switch

B. 3 terminal bilateral switch

C. 2 terminal bilateral switch

D. 2 terminal switch

59. Delay time is defined by the interval when_______________?
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A. anode voltage drops from 100 % to 90 % of its actual value

B. all of these

C. gate current increases from 90 % to 100 % of its final value

D. anode current reaches 10 % from forward leakage current

60. An RC snubber network used in BJT__________?
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A. Divert the collector current during turn off

B. Dissipates a fair amount of switching power

C. All of these

D. Improves the reverse bias safe operating area

61. For an SCR gate aEUR" cathode characteristic is a straight line of 130. For triggered source volume of 15 V and allowable gate power dissipation of 0.5 W compute the gate source resistance_____?
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A. 108 I.

B. 111.9 I.

C. 11.19 I.

D. 115 I

62. 4 thyristors rated 200 V in series. The operating voltage of the string is 600 V. Derating factor of the string is_____________________?
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A. 0.2

B. 0.25

C. 0.7

D. 0.75

63. Rise time is defined by the interval when____________?
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A. gate current rises from 90 % to 100 % of it final value

B. anode voltage drops from 90 % to 10 % of its initial value

C. anode current rises 10 % to 90 % of its final value

D. both B and C
64. CB used for over current protection of thyristor operates when the fault current is__________?
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A. of long period

B. of short duration

C. both (A) and (B)

D. neither (A) nor (B)

65. In forward blocking mode of a thyristor________?
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A. Junction J1, J3 is in reverse bias and J2 is in forward bias.

B. junction J3 is in forward bias and J1, J2 is in reverse bias.

C. junction J2 is in reverse bias and J1, J3 is in forward bias.

D. Junction J1 and J2 is in forward bias and J3 is in reverse bias.

66. In a 3 phase CSI, if the required line output voltages are balanced and 120 degree out of phase, then the chopping angles are used to eliminate only the harmonics at frequencies
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A. All of these

B. 11

C. 5

D. 7

67. Harmonics in 3 phase inverters can be reduced by using___________?
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A. Passive filter

B. Active filter

C. Both passive and active filters

D. None of these

68. In a flyback converter, the inductor of the buck-boost converter has been replaced by a_____________?
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A. Flyback transistor

B. Flyback capacitor

C. Flyback resistor

D. Flyback transformer
69. During gate recovery time_____________?
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A. charge carriers of J3 junction is removed

B. charge carrier of J1 junction removed

C. charge carriers of J2 junction is swept out

D. charge carriers of J2 junction recombined
70. The sum of all phase current in a star connected primary winding with no neutral connection is equal to___________?
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A. Three times the line current

B. Zero at all times

C. Three times the phase current

D. Phase current

71. Maximum power loss occurs during_________________?
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A. rise time

B. all

C. delay time

D. spread time

72. In ac dc conversion, when the switch is closed then the sum of voltages around the loop is____________?
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A. Non zero

B. Zero

C. Twice of the voltage when switch is open

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

73. Thermal voltage VT can be given by____________?
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A. (K2/q)(T + 1/T 1)

B. qT/K

C. KT/q

D. Kq/T

74. A power semiconductor may undergo damage due to____________?
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A. Low di/dt

B. High dv/dt

C. Low dv/dt

D. High di/dt
75. A single phase one pulse controlled circuit has a resistance R and counter emf E load 400 sin(314 t) as the source voltage. For a load counter emf of 200 V, the range of firing angle control is _____?
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A. 30 to 180.

B. 60 to 180.

C. 30 to 150.

D. 60 to 120.

76. If the firing angle becomes negative, then the rectifier begins to work as_______________?
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A. A regulator

B. An inverter

C. A rectifier

D. A chopper

77. For similar carrier and modulating signals, the line current used in CSI is_____________?
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A. Identical to phase voltage in CSI

B. Identical to phase voltage in VSI

C. Identical to line voltage in a VSI

D. Identical to line current in VSI

78. Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of_______________?
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A. AC input power to the transformer volt amp rating required by secondary

B. DC output power to the transformer volt amp rating required by primary

C. DC output power to the transformer volt amp rating required by secondary

D. AC input power to the transformer volt amp rating required by primary

79. The advantage of using free wheeling diode in half controlled bridge converter is that
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A. There is always a path for the ac current independent of the ac line

B. There is always a path for the dc 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

80. In the operation and control of both naturally commutated and forced commutated SCR base converter, commutation plays an important role. The converters is / are ___________?
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A. All of these

B. DC AC

C. AC DC

D. DC DC

81. What is the advantage of HRC fuses over Rewirable fuses?
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A. All of the above

B. High rupturing capacity

C. High speed operation

D. No ageing effect

82. An SCR is made up of silicon because?
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A. silicon has small leakage voltage than germanium

B. silicon has small leakage current than germanium

C. silicon has large leakage voltage than germanium

D. silicon has large leakage current than germanium

83. The turn-on time of an SCR with inductive load is 20 s. The puls train frequency is 2.5 KHz with a mark/space ratio of 1/10, then SCR will___________?
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A. Turn on if pulse frequency us increased to two times

B. Not turn on

C. Turn on

D. Turn on if inductance is removed

84. Which one is most suitable power device for high frequency (>100 KHz) switching application?
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A. BJT

B. Schottky diode

C. Microwave transistor

D. Power MOSFET
85. In variable frequency, PWM gain
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A. Phase lead helps to increase the phase margin of the control loop

B. Phase lag helps to decrease the phase margin of the control loop

C. Phase lag helps to increase the phase margin of the control loop

D. Phase lead helps to decrease the phase margin of the control loop

86. A thyristor is basically________?
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A. A set of SCRs

B. PNPN device

C. A set if SCR,diac and triac

D. A combination of diac and triac

87. A carrier based PWM technique in CSI is composed of____________?
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A. A switching and shorting pulse combination

B. All of these

C. A switching pulse generator and a shorting pulse generator

D. A shorting pulse distributor

88. Under harmonic free load voltages, the 3 phase VSI_____________?
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A. Does not contains fifth harmonic

B. Does not contains seventh harmonic

C. Does not contains second harmonic

D. Does not contains third harmonic

89. Dynamic equalising circuit is useful____________?
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A. To limit di / dt of SCR

B. To limit dV / dt of SCR

C. For voltage equalisation

D. Both B and C
90. A single phase ac dc converter is also known as____________?
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A. rectifier

B. regulator

C. chopper

D. inverter

91. A MOSFET, for its conduction uses_____________?
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A. Only minority carriers

B. Only majority carriers

C. Both minority and majority carriers

D. None of these

92. The power demand can be estimated approximately by____________?
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A. Mathematical method

B. Load survey method

C. Statistical method

D. Economic parameters

93. In a load commutated DC DC chopper, the capacitor has a_____________?
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A. Symmetric trapezoidal voltage across itself

B. Symmetric rectangular voltage across itself

C. Symmetric triangular voltage across itself

D. Symmetric sinusoidal voltage across itself

94. AC power in a load can be controlled by using____________?
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A. Three SCRs in series

B. Two SCRs in parallel opposition

C. Four SCRs in series

D. Two SCRs in series

95. If all the SCRs of 3 phase PAC is replaced by diodes, they would be triggered_____________?
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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. 60 degree before the zero crossing of the corresponding line voltages

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

96. As the breakdown voltage reached, the DIAC exhibits?
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A. All of these

B. Goes into avalanche condition

C. Voltage drop snaps back

D. Negative resistance characteristics

97. The square wave operation of 3 phase VSI lines contains the harmonics. The amplitudes are____________?
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A. None of these

B. Directly proportional to their harmonic order

C. Inversely proportional to their harmonic order

D. Not related to their harmonic order

98. In a square wave operation of 3 phase CSIs, the power values are on for___________?
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A. 90 degree

B. 150 degree

C. 120 degree

D. 60 degree

99. In a push pull converter, the filter capacitor can be obtained as____________?
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A. Cmin= ( 1 2 D ) V / 32 ( Vr L f2 )

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

C. Cmin = V / ( Vr L f2 )

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

100. DIAC and TRIAC both are semiconductors devices and conduct in____________________?
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A. DIAC conducts in forward direction and TRIAC conducts in reverse direction

B. Both conducts in forward direction

C. Both conducts in reverse direction

D. Both conducts in either direction