Top 250+ Solved Power Electronics MCQ Questions Answer
Q. Very large values of modulation index (greater than 3.24) lead to
a. Square AC output voltage
b. Sine AC output voltage
c. Triangular AC output voltage
d. Trapezoidal AC output voltage
Q. With increase in firing angle
a. Both harmonic distortion and quality of input current increases
b. Harmonic distortion increases and quality of input current decreases
c. Harmonic distortion decreases and quality of input current increases
d. Both harmonic distortion and quality of input current decreases
Q. The advantage of using free - wheeling diode in half controlled bridgeconverter is that
a. There is always a path for the dc current independent of the ac line
b. There is always a path for the ac 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
Q. The input current waveform of a bridge controlled rectifier when the load isperfectly filtered is
a. Sine wave
b. Square wave
c. Saw - tooth wave
d. Trapezoidal wave
Q. A full wave rectifier with resistive load produces
a. Second harmonic
b. Third harmonic
c. Fifth harmonic
d. Do not produce harmonics
Q. If all the SCR’s of 3 phase PAC is replaced by diodes, they would betriggered
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. 120 degree before the zero crossing of the corresponding line voltages
d. 60 degree before the zero crossing of the corresponding line voltages
Q. An RC snubber network used in BJT
a. Divert the collector current during turn - off
b. Improves the reverse bias safe operating area
c. Dissipates a fair amount of switching power
d. All of these
Q. In a 3 phase half wave rectifier, when firing angle is less than 90 degree,then the average dc output voltage becomes
a. Positive
b. Negative
c. Zero
d. None of these
Q. In dual converters,
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
Q. A single phase ac - dc converter is also known as
a. rectifier
b. inverter
c. chopper
d. regulator
Q. The two-transistor model of a thyristor consists of two transistors :
a. one n-p-n and other p-n-p
b. both p-n-p
c. both n-p-n
d. one n-p-n and other UJT
Q. In a thyristor, the forward breakover voltage
a. is constant
b. may be constant or may depend on gate current
c. decreases as gate current is increased
d. increases as gate current is increased
Q. The gate lead, in a thyristor is welded to :
a. p layer to which anode is connected
b. n layer nearest to the anode terminal
c. p layer nearest to the cathode terminal
d. outside n layer
Q. In a 3 phase full converter, the firing angle is less than 60°. The instantaneous output voltage
a. will have positive part only
b. will have both positive and negative parts
c. may have both positive and negative parts
d. will have negative part if load is inductive
Q. In a stud mounted SCR, the stud is
a. in thermal contact with heat sink
b. insulated from heat sink
c. in electrical and thermal contact with heat sink
d. in either electrical or thermal contact with heat sink