Free Power Electronics MCQs with Answers
253 Power Electronics MCQs from Electrical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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253 questions · page 7 of 13
- A. Positive voltage at the gate terminal
- B. Negative voltage at the gate terminal
- C. Either (a) or (b)
- D. None of these
Explanation: A TRIAC is bidirectional and can be triggered by either a positive or negative gate current relative to its reference terminal, although…
Correct answer: Either (a) or (b)- A. Time domain
- B. Frequency domain
- C. Either A. or B.
- D. None of these
Explanation: PWM converter transfer functions are commonly obtained using averaged time-domain equations and then expressed in the frequency or…
Correct answer: Either A. or B.- A. DIAC conducts in forward direction and TRIAC conducts in reverse direction
- B. Both conducts in forward direction
- C. Both conducts in reverse direction
- D. Both conducts in either direction
Explanation: A DIAC is a bidirectional trigger device, and a TRIAC conducts current in either direction after triggering.
Correct answer: Both conducts in either direction- A. Current transformer
- B. Potential transformer
- C. Power transformer
- D. SCR
Explanation: A Graetz bridge is a full-wave bridge rectifier that uses both halves of the AC waveform without requiring a centre-tapped secondary…
Correct answer: Power transformer- A. A rectifier
- B. An inverter
- C. A chopper
- D. A regulator
Explanation: With a negative firing angle, power flows from the DC side back toward the AC supply, so the controlled converter operates in inversion…
Correct answer: An inverter- A. Phase lead helps to increase the phase margin of the control loop
- B. Phase lag helps to increase the phase margin of the control loop
- C. Phase lead helps to decrease the phase margin of the control loop
- D. Phase lag helps to decrease the phase margin of the control loop
Explanation: A phase-lead compensator adds positive phase near the crossover frequency, increasing the phase margin and generally improving dynamic…
Correct answer: Phase lead helps to increase the phase margin of the control loop- A. Positive
- B. Negative
- C. Zero
- D. None of these
Explanation: For a three-phase half-wave controlled rectifier, the average output remains positive when the firing angle is below 90 degrees.
Correct answer: Positive- A. AC input power to the transformer volt - amp rating required by secondary
- B. AC input power to the transformer volt - amp rating required by primary
- C. DC output power to the transformer volt - amp rating required by secondary
- D. DC output power to the transformer volt - amp rating required by primary
Explanation: Transformer utilization factor compares useful DC output power with the transformer VA rating, normally based on the required secondary VA…
Correct answer: DC output power to the transformer volt - amp rating required by secondary- A. A switching pulse generator and a shorting pulse generator
- B. A shorting pulse distributor
- C. A switching and shorting pulse combination
- D. All of these
Explanation: Carrier-based PWM for a current-source inverter must generate normal switching pulses as well as controlled shorting pulses and distribute…
Correct answer: All of these- A. 60 degree
- B. 90 degree
- C. 120 degree
- D. 150 degree
Explanation: In square-wave operation of a three-phase current-source inverter, each conducting path or valve remains active for 120 degrees of an…
Correct answer: 120 degree- A. Rms value of the ac component of load voltage to the dc voltage
- B. Average value of the ac component of load voltage to the peak value of voltage
- C. Average value of the dc component of load voltage to the ac voltage
- D. Peak value of the dc component of load voltage to the ac voltage
Explanation: Ripple factor measures the unwanted AC content relative to the useful DC component, so it is the RMS value of the AC load-voltage…
Correct answer: Rms value of the ac component of load voltage to the dc voltage- A. Root mean square value of voltage and current to its peak value
- B. Root mean square value of voltage and current to its average value
- C. Average value of current and voltage to its root mean square value
- D. Peak value of current and voltage to its root mean square value
Explanation: Form factor compares the effective heating value of a waveform with its average value, giving RMS voltage or current divided by the…
Correct answer: Root mean square value of voltage and current to its average value- A. By applying a gate pulse and turned off only when current becomes zero
- B. And turned off by applying gate pulse
- C. By applying a gate pulse and turned off by removing the gate pulse
- D. By making current non zero and turned off by making current zero
Explanation: An SCR is triggered into conduction by a gate pulse, but the gate cannot turn it off.
Correct answer: By applying a gate pulse and turned off only when current becomes zero- A. Two SCR's connected in reverse parallel
- B. Two SCR's connected in parallel
- C. Two SCR's connected in series
- D. Two BJT's connected in series
Explanation: A TRIAC is equivalent to two SCRs connected in anti-parallel, allowing current control in both directions.
Correct answer: Two SCR's connected in reverse parallel- A. both as forward characteristics
- B. both as reverse characteristics
- C. former as forward characteristics and later as reverse characteristics
- D. former as reverse characteristics and later as forward characteristics
Explanation: With the anode positive relative to the cathode, the SCR operates in its forward characteristic region; with the anode negative, it…
Correct answer: former as forward characteristics and later as reverse characteristics- A. as static conductor
- B. for power control
- C. for speed control of dc shunt motor
- D. All of these
Explanation: An SCR acts as a static switch, controls electrical power, and can regulate the speed of a DC shunt motor by varying its applied voltage.
Correct answer: All of these- A. voltage sensitive load from excessive dc power supply output voltages
- B. current sensitive load from excessive dc power supply output voltages
- C. voltage sensitive load from excessive ac power supply output voltages
- D. current sensitive load from excessive ac power supply output voltages
Explanation: A crowbar rapidly short-circuits or clamps an excessive DC supply voltage, causing protection circuitry to disconnect the supply before…
Correct answer: voltage sensitive load from excessive dc power supply output voltages- A. Diode
- B. BJT
- C. SCR
- D. TRIAC
Explanation: A TRIAC conducts in either direction when triggered, unlike a diode or SCR, which are normally unidirectional devices.
Correct answer: TRIAC- A. Sine wave
- B. Square wave
- C. Saw - tooth wave
- D. Trapezoidal wave
Explanation: With a perfectly smoothed load current, each bridge pair conducts for approximately half a cycle, so the source current reverses abruptly…
Correct answer: Square wave140. The IGBT resulted in higher switching speed and lower energy losses. It can be used for___________?
- A. Uninterruptible power supplies
- B. Induction heating system
- C. Constant voltage and frequency power supplies
- D. All of these
Explanation: IGBTs combine easy gate control with high switching speed and low conduction loss, making them suitable for UPS units, induction-heating…
Correct answer: All of these