61. The SCR is turned ON by
A) Forward voltage only
B) Gate current pulse
C) Reverse voltage
D) Open gate
Answer: B) Gate current pulse
62. The device which conducts current in both directions when triggered is
A) SCR
B) TRIAC
C) DIAC
D) MOSFET
Answer: B) TRIAC
63. A DIAC conducts current when
A) Forward biased
B) Reverse biased
C) Breakover voltage is reached
D) Gate signal applied
Answer: C) Breakover voltage is reached
64. In SCR, forward breakover voltage is the voltage at which
A) SCR turns OFF
B) SCR turns ON without gate signal
C) SCR conducts in reverse direction
D) None
Answer: B) SCR turns ON without gate signal
65. The maximum voltage that an SCR can block in the forward direction is
A) Forward blocking voltage
B) Reverse voltage
C) Holding voltage
D) Firing voltage
Answer: A) Forward blocking voltage
66. The device which can control both AC and DC power is
A) TRIAC
B) DIAC
C) SCR
D) BJT
Answer: A) TRIAC
67. The region where SCR does not conduct even though forward biased is
A) Forward blocking region
B) Forward conduction region
C) Reverse blocking region
D) Breakdown region
Answer: A) Forward blocking region
68. When the SCR is ON, it behaves like a
A) High resistance path
B) Open circuit
C) Closed switch
D) Diode
Answer: C) Closed switch
69. The forward current rating of a power diode depends on
A) Temperature
B) Junction area
C) Material
D) All of these
Answer: D) All of these
70. The on-state voltage drop of a silicon diode is approximately
A) 0.1 V
B) 0.3 V
C) 0.7 V
D) 2 V
Answer: C) 0.7 V
71. When SCR conducts, its anode-cathode voltage is
A) Very high
B) Very low
C) Zero
D) Reverse biased
Answer: B) Very low
72. The holding current of SCR is generally
A) Greater than latching current
B) Less than latching current
C) Equal to latching current
D) Unrelated
Answer: B) Less than latching current
73. Power MOSFETs are preferred for
A) Low-frequency applications
B) High-frequency applications
C) Constant speed drives
D) DC motors only
Answer: B) High-frequency applications
74. IGBT can handle
A) Only voltage
B) Only current
C) Both high voltage and current
D) Only low power
Answer: C) Both high voltage and current
75. The static V–I characteristic of SCR consists of
A) Three regions
B) Two regions
C) One region
D) Four regions
Answer: A) Three regions
76. The time during which SCR regains forward blocking ability after conduction is
A) Turn-on time
B) Turn-off time
C) Recovery time
D) Conduction time
Answer: B) Turn-off time
77. In a DC chopper, the average output voltage is controlled by
A) Firing angle
B) Duty cycle
C) Load resistance
D) Supply frequency
Answer: B) Duty cycle
78. The main function of a converter is to
A) Convert AC to DC
B) Convert DC to AC
C) Step up AC
D) Store energy
Answer: A) Convert AC to DC
79. Inverter output frequency depends on
A) Supply voltage
B) Switching frequency
C) Gate current
D) Load resistance
Answer: B) Switching frequency
80. The input of an inverter is
A) AC
B) DC
C) Pulsating DC
D) Variable voltage
Answer: B) DC
81. The process of turning OFF an SCR is called
A) Commutation
B) Firing
C) Triggering
D) Rectification
Answer: A) Commutation
82. The turn-on time of SCR depends on
A) Gate current
B) Anode voltage
C) Temperature
D) All of these
Answer: D) All of these
83. The device used to control AC voltage is
A) Diode
B) TRIAC
C) IGBT
D) MOSFET
Answer: B) TRIAC
84. The maximum reverse voltage that a diode can withstand is
A) Peak inverse voltage (PIV)
B) Forward voltage
C) Breakdown voltage
D) Cut-in voltage
Answer: A) Peak inverse voltage (PIV)
85. The device that acts as an electronic switch is
A) SCR
B) TRIAC
C) MOSFET
D) All of these
Answer: D) All of these
86. The phase control in an SCR circuit is achieved by changing
A) Anode voltage
B) Firing angle
C) Load
D) Frequency
Answer: B) Firing angle
87. The reverse blocking voltage of SCR is less than
A) Forward blocking voltage
B) Breakdown voltage
C) Supply voltage
D) None
Answer: A) Forward blocking voltage
88. The device which can conduct current in both directions without gate control is
A) DIAC
B) TRIAC
C) SCR
D) BJT
Answer: A) DIAC
89. The number of layers in a TRIAC is
A) Two
B) Three
C) Four
D) Six
Answer: D) Six
90. In a resistive load, voltage and current are
A) In phase
B) Out of phase
C) Opposite in direction
D) Equal
Answer: A) In phase
91. The power semiconductor device that has no gate terminal is
A) SCR
B) TRIAC
C) DIAC
D) IGBT
Answer: C) DIAC
92. The main function of DIAC in a TRIAC circuit is to
A) Provide symmetrical triggering
B) Reduce voltage
C) Amplify current
D) Increase conduction
Answer: A) Provide symmetrical triggering
93. A MOSFET is a
A) Current-controlled device
B) Voltage-controlled device
C) Thermal device
D) Magnetic device
Answer: B) Voltage-controlled device
94. The type of commutation used in DC choppers is
A) Natural commutation
B) Forced commutation
C) Voltage commutation
D) Resonant commutation
Answer: B) Forced commutation
95. A power diode is used in rectifiers to
A) Amplify signals
B) Control voltage
C) Convert AC to DC
D) Store energy
Answer: C) Convert AC to DC
96. The output of an inverter is
A) DC
B) AC
C) Constant voltage
D) Pulsating DC
Answer: B) AC
97. The most commonly used commutation method in DC choppers is
A) Voltage commutation
B) Current commutation
C) Load commutation
D) Class C commutation
Answer: C) Load commutation
98. The main loss in a power diode is
A) Switching loss
B) Conduction loss
C) Leakage loss
D) Magnetic loss
Answer: B) Conduction loss
99. A single-phase half-wave rectifier uses
A) One SCR
B) Two SCRs
C) Four SCRs
D) Six SCRs
Answer: A) One SCR
100. The input of a converter is
A) AC
B) DC
C) Pulsating DC
D) Constant voltage
Answer: A) AC
101. The device which turns ON by itself when forward voltage exceeds breakover voltage is
A) DIAC
B) TRIAC
C) SCR
D) BJT
Answer: C) SCR
102. The type of commutation used in an inverter is
A) Forced commutation
B) Natural commutation
C) Resonant commutation
D) Voltage commutation
Answer: A) Forced commutation
103. A rectifier converts
A) AC to DC
B) DC to AC
C) DC to DC
D) AC to AC
Answer: A) AC to DC
104. A PWM inverter is used to
A) Reduce harmonics
B) Increase frequency
C) Reduce voltage
D) Increase current
Answer: A) Reduce harmonics
105. The conduction in an SCR starts when
A) Gate current flows
B) Anode current becomes zero
C) Reverse voltage applied
D) None
Answer: A) Gate current flows
106. The main purpose of a snubber circuit is
A) Protect SCR from high dv/dt
B) Reduce firing angle
C) Increase speed
D) Regulate voltage
Answer: A) Protect SCR from high dv/dt
107. The SCR remains ON even after gate signal is removed because
A) Internal latch-up
B) High leakage current
C) Thermal effect
D) It’s bistable
Answer: A) Internal latch-up
108. When SCR is reverse biased, it behaves as
A) Open circuit
B) Short circuit
C) Conducting diode
D) Resistor
Answer: A) Open circuit
109. The most suitable device for low voltage, high frequency applications is
A) BJT
B) MOSFET
C) IGBT
D) TRIAC
Answer: B) MOSFET
110. The control range of firing angle in a full converter is
A) 0°–90°
B) 0°–180°
C) 90°–270°
D) 0°–360°
Answer: B) 0°–180°
111. The full-wave bridge rectifier requires
A) 2 diodes
B) 4 diodes
C) 6 diodes
D) 8 diodes
Answer: B) 4 diodes
112. The device used to smooth DC output in converters is
A) Resistor
B) Inductor
C) Capacitor
D) Transformer
Answer: C) Capacitor
113. The commutation method used in AC circuits is
A) Natural
B) Forced
C) Voltage
D) Current
Answer: A) Natural
114. In a half-wave rectifier, the efficiency is about
A) 20%
B) 40.6%
C) 60%
D) 81.2%
Answer: B) 40.6%
115. The ripple factor of a full-wave rectifier is
A) 1.21
B) 0.482
C) 0.812
D) 2.0
Answer: B) 0.482
116. The efficiency of a bridge rectifier is
A) 50%
B) 81.2%
C) 100%
D) 25%
Answer: B) 81.2%
117. The conduction angle of a full converter is
A) 0°–90°
B) 0°–180°
C) 0°–360°
D) 180°–360°
Answer: B) 0°–180°
118. The SCR is used as
A) Amplifier
B) Switch
C) Oscillator
D) Rectifier only
Answer: B) Switch
119. The phase control technique is used in
A) AC voltage controllers
B) DC choppers
C) Inverters
D) Amplifiers
Answer: A) AC voltage controllers
120. The gate current of SCR is in the range of
A) mA
B) µA
C) A
D) V
Answer: A) mA
121. The forward current rating of SCR depends on
A) Junction temperature
B) Gate voltage
C) Supply voltage
D) Load
Answer: A) Junction temperature
122. The gate of an SCR is made of
A) Silicon
B) Germanium
C) Graphite
D) Metal
Answer: A) Silicon
123. The SCR remains in OFF state when
A) Reverse biased
B) Forward biased with no gate current
C) Both A and B
D) None
Answer: C) Both A and B
124. The average output voltage of a half-wave rectifier is
A) 0.318 Vm
B) 0.637 Vm
C) 0.707 Vm
D) 0.5 Vm
Answer: A) 0.318 Vm
125. The average output voltage of a full-wave rectifier is
A) 0.318 Vm
B) 0.637 Vm
C) 0.707 Vm
D) 1 Vm
Answer: B) 0.637 Vm
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