Power Electronics Multiple Choice Questions and Answers

121. 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

122. 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

123. The triac is …………….

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

124. The UJT may be used as ……………….

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

125. 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

126. 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

127. 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

128. 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

129. Unipolar modulation is generally used in

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

130. 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