101. In a single-phase full converter with resistive load, the output voltage waveform is
A) Pure DC
B) Pulsating DC
C) AC
D) None
Answer: B) Pulsating DC
102. The input power factor of a fully-controlled converter is
A) Unity
B) Lagging
C) Leading
D) Zero
Answer: B) Lagging
103. In an SCR, turn-on time is mainly decided by
A) Gate circuit parameters
B) Load inductance
C) Supply voltage
D) Reverse voltage
Answer: A) Gate circuit parameters
104. A freewheeling diode is used in converter circuits to
A) Reduce commutation failure
B) Reduce load current ripple
C) Improve power factor
D) Maintain current continuity
Answer: D) Maintain current continuity
105. The latching current of an SCR is always
A) Greater than holding current
B) Less than holding current
C) Equal to holding current
D) Unrelated to holding current
Answer: A) Greater than holding current
106. A cycloconverter converts
A) Fixed DC to variable DC
B) Fixed AC to variable AC
C) Fixed DC to fixed AC
D) Variable DC to variable AC
Answer: B) Fixed AC to variable AC
107. The main function of snubber circuit is to
A) Protect SCR from overvoltage
B) Limit di/dt and dv/dt
C) Smooth output voltage
D) Trigger SCR
Answer: B) Limit di/dt and dv/dt
108. The commutation method used in DC choppers is
A) Line commutation
B) Forced commutation
C) Natural commutation
D) Self-commutation
Answer: B) Forced commutation
109. The basic principle of inverter operation is
A) Phase control
B) Reverse operation of rectifier
C) Transformer coupling
D) Resonance
Answer: B) Reverse operation of rectifier
110. Inverters using SCRs require
A) Forced commutation
B) Natural commutation
C) No commutation
D) Voltage commutation only
Answer: A) Forced commutation
111. The turn-off time of an SCR decreases with
A) Temperature increase
B) Increase in current
C) Decrease in current
D) Increase in supply voltage
Answer: C) Decrease in current
112. In a single-phase full converter feeding RL load, the output voltage depends on
A) Firing angle
B) Supply frequency
C) Load current
D) Transformer ratio
Answer: A) Firing angle
113. Power MOSFETs are preferred for high-frequency applications because
A) Low input capacitance
B) High switching speed
C) High current rating
D) High voltage rating
Answer: B) High switching speed
114. The most commonly used device in SMPS is
A) SCR
B) BJT
C) MOSFET
D) TRIAC
Answer: C) MOSFET
115. The maximum efficiency of DC-DC converter is limited by
A) Switching losses
B) Load resistance
C) Duty cycle
D) Voltage ratio
Answer: A) Switching losses
116. In a step-down chopper, the duty cycle increases with
A) Increase in output voltage
B) Decrease in output voltage
C) Increase in frequency
D) Decrease in load
Answer: A) Increase in output voltage
117. The power factor of an uncontrolled bridge rectifier feeding resistive load is
A) 0.707
B) 1
C) 0.9
D) 0.5
Answer: B) 1
118. The dynamic characteristics of an SCR are affected by
A) Junction temperature
B) Gate resistance
C) dv/dt
D) All of the above
Answer: D) All of the above
119. GTO differs from SCR in that it
A) Cannot be turned off by gate
B) Can be turned off by gate signal
C) Requires forced commutation
D) Works only on DC
Answer: B) Can be turned off by gate signal
120. The control of output voltage in AC voltage controller is by
A) Phase control
B) Integral control
C) Feedback control
D) Frequency control
Answer: A) Phase control
121. In PWM inverter, output voltage control is achieved by
A) Varying frequency
B) Varying pulse width
C) Varying phase
D) Varying amplitude
Answer: B) Varying pulse width
122. The main disadvantage of MOSFET in power electronics is
A) High input impedance
B) High switching loss
C) Low voltage rating
D) Poor efficiency
Answer: C) Low voltage rating
123. The total harmonic distortion (THD) of inverter output depends on
A) PWM pattern
B) Load resistance
C) Input voltage
D) Frequency
Answer: A) PWM pattern
124. The regenerative braking in DC motor is possible when
A) Back emf > supply voltage
B) Supply voltage > back emf
C) Armature current is zero
D) Field current is constant
Answer: A) Back emf > supply voltage
125. The average output voltage of single-phase half-wave controlled rectifier is
A) (Vm/π)(1+cosα)
B) Vm/π
C) Vm(1+cosα)/2
D) Vm/2
Answer: C) Vm(1+cosα)/2
126. In a boost converter, the output voltage is
A) Less than input
B) Equal to input
C) Greater than input
D) Zero
Answer: C) Greater than input
127. For buck converter, the output voltage is
A) Vo = D × Vin
B) Vo = Vin/D
C) Vo = Vin × (1−D)
D) Vo = Vin²/D
Answer: A) Vo = D × Vin
128. The device used for high-frequency switching is
A) SCR
B) BJT
C) MOSFET
D) TRIAC
Answer: C) MOSFET
129. The inverter which can control both frequency and voltage is
A) Voltage source inverter
B) Current source inverter
C) Cycloconverter
D) PWM inverter
Answer: D) PWM inverter
130. The reverse recovery time of diode affects
A) Switching losses
B) Load current
C) Conduction losses
D) Power factor
Answer: A) Switching losses
131. The main advantage of IGBT over MOSFET is
A) High input impedance
B) High current handling capacity
C) Low switching speed
D) Low conduction loss
Answer: B) High current handling capacity
132. The input to chopper is
A) DC
B) AC
C) Pulsating AC
D) Sinusoidal AC
Answer: A) DC
133. Commutation circuit in inverter helps in
A) Turning ON SCR
B) Turning OFF SCR
C) Triggering TRIAC
D) Reducing noise
Answer: B) Turning OFF SCR
134. The filter in converter circuit reduces
A) Ripple
B) Power
C) Frequency
D) Resistance
Answer: A) Ripple
135. The major loss in power semiconductor device is
A) Conduction loss
B) Switching loss
C) Leakage loss
D) Dielectric loss
Answer: B) Switching loss
136. The safe operating area (SOA) of device is defined by
A) Voltage and current limits
B) Frequency and temperature
C) Power and voltage
D) Temperature and gain
Answer: A) Voltage and current limits
137. Inverter output voltage can be made sinusoidal by
A) Filtering
B) Reducing frequency
C) Increasing switching frequency
D) Both A and C
Answer: D) Both A and C
138. The PWM control provides
A) Reduced harmonic distortion
B) Constant output frequency
C) Both A and B
D) None
Answer: C) Both A and B
139. The reverse recovery charge of diode increases with
A) Temperature
B) Forward current
C) Reverse voltage
D) All
Answer: D) All
140. The heat sink is used to
A) Increase current
B) Dissipate heat
C) Reduce losses
D) Control firing
Answer: B) Dissipate heat
141. The dv/dt rating of SCR is
A) Maximum rate of rise of forward voltage
B) Minimum gate current
C) Holding current
D) Average current
Answer: A) Maximum rate of rise of forward voltage
142. When SCR is forward biased but gate not triggered, it is in
A) Forward blocking state
B) Forward conduction
C) Reverse blocking
D) Reverse conduction
Answer: A) Forward blocking state
143. The purpose of snubber is to
A) Limit dv/dt
B) Reduce heating
C) Reduce losses
D) Increase speed
Answer: A) Limit dv/dt
144. The on-state voltage drop of SCR is typically
A) 0.7 V
B) 1–2 V
C) 3–5 V
D) 10 V
Answer: B) 1–2 V
145. The turn-on time of GTO is
A) Longer than SCR
B) Shorter than SCR
C) Equal to SCR
D) Independent
Answer: B) Shorter than SCR
146. The chopper frequency is
A) Few Hz
B) Few kHz
C) Few MHz
D) 50 Hz
Answer: B) Few kHz
147. The output of inverter can be controlled by
A) PWM
B) Phase shift
C) Frequency variation
D) All of these
Answer: D) All of these
148. The output voltage of single-phase inverter is
A) AC
B) DC
C) Pulsating DC
D) None
Answer: A) AC
149. The ideal switch has
A) Zero on resistance
B) Infinite off resistance
C) Both A and B
D) None
Answer: C) Both A and B
150. The IGBT combines the features of
A) BJT and MOSFET
B) SCR and TRIAC
C) BJT and GTO
D) FET and Diode
Answer: A) BJT and MOSFET
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