Power Electronics MCQs Quiz Multiple Choice Questions & Answers Page 3

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

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

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

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

103. In radiative coupling, the emitter radiation field

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

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

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

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

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

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

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

107. Silicon controlled rectifier can be turned on

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

108. Single phase VSI are mainly used in

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

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

110. The conduction losses in IGBT is

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

111. The device that does not have the gate terminal is ……………….

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

112. The device that exhibits negative resistance region is ………………..

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

113. The effects of EMI can be reduced by

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

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

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

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

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

116. The normal way to turn on a diac is by ………………..

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

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

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

118. The power MOSFET device is a

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

119. The square wave operation of 3 phase VSI lines contains the harmonics. The amplitudes are

1. Inversely proportional to their harmonic order
2. Not related to their harmonic order
3. Directly proportional to their harmonic order
4. None of these

120. The switching function of semiconductor devices can be characterized with

1. Frequency only
2. Duty ratio and frequency
3. Duty ratio only
4. Duty ratio, frequency and time delay

121. The triac is …………….

1. A four-terminal device
2. Not a thyristor
3. Like a bidirectional SCR
4. Answers (1) and (2)

122. The UJT may be used as ……………….

1. A sawtooth generator
2. A rectifier
3. Am amplifier
4. None of the above

123. The V-I characteristics for a triac in the first and third quadrants are essentially identical to those of ………………. in its first quadrant

1. SCR
2. UJT
3. Transistor
4. none of the above

124. To turn on UJT, the forward bias on the emitter diode should be …………… the peak point voltage

1. Equal to
2. More than
3. Less than
4. None of the above

125. TRIAC is a semiconductor power electronic device which contains

1. Two SCRs connected in parallel
2. Two SCRs connected in series
3. Two SCRs connected in reverse parallel
4. Two BJTs connected in series

126. Under harmonic free load voltages, the 3 phase VSI

1. Does not contains third harmonic
2. Does not contains fifth harmonic
3. Does not contains second harmonic
4. Does not contains seventh harmonic

127. Unipolar modulation is generally used in

1. AC – DC converters
2. DC – AC converters
3. AC – AC converters
4. DC – DC converters

128. Very large values of modulation index (greater than 3.24 lead to)

1. Sine AC output voltage
2. Triangular AC output voltage
3. Square AC output voltage
4. Trapezoidal AC output voltage

129. Voltage commutation circuit can be converted into a current commutation by interchanging the positions of

1. Capacitor and SCR
2. Inductor and capacitor
3. Diode and capacitor
4. Capacitor and load

130. When a UJT is turned ON, the resistance between emitter terminal and lower base terminal …………….

1. Is decreased
2. Is increased
3. Remains the same
4. None of the above

131. When the emitter terminal of a UJT is open, the resistance between the base terminal is generally ………………..

1. Low
2. Extremely low
3. High
4. None of the above

132. When the temperature increases, the inter-base resistance (RBB) of a UJT ………….

1. Decreases
2. Remains the same
3. Increases
4. None of the above

133. When the temperature increases, the intrinsic stand off ratio ……….

1. Decreases
2. Essentially remains the same
3. Increases
4. None of the above

134. Which of the following is not a characteristic of UJT?

1. Negative resistance
2. Peak-point voltage
3. Intrinsic stand off ratio
4. Bilateral conduction

135. With increase in firing angle

1. Harmonic distortion increases and quality of input current decreases
2. Harmonic distortion decreases and quality of input current increases
3. Both harmonic distortion and quality of input current increases
4. Both harmonic distortion and quality of input current decreases

136. A Diac is a ................. switch

1. A dc
2. A mechanical
3. An c
4. none of the above