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 12 of 13
- A. Use of snubber circuit.
- B. Using heat sink.
- C. Using CB and fuse.
- D. Using equalizing circuit
Explanation: Thermal protection is obtained by conducting heat away from the SCR, and a heat sink provides the required low-resistance path to the…
Correct answer: Using heat sink.- A. Controlled transistor
- B. Controlled switch
- C. Amplifier with higher gain
- D. Amplifier with large current gain
Explanation: A thyristor has an essentially stable OFF state and, once triggered, changes to a conducting ON state that it latches into.
Correct answer: Controlled switch- A. lower power circuit.
- B. high power circuit.
- C. magnetic circuit.
- D. may be low power or high power circuit
Explanation: The gate only initiates conduction and requires a small triggering pulse compared with the main anode-cathode power circuit.
Correct answer: lower power circuit.- A. 600 V/µs
- B. 800 V/µs
- C. 1200 V/µs
- D. 1000 V/µs
Explanation: The charging current is I = C(dv/dt), so dv/dt = 16 mA / 20 pF = 8 × 10^8 V/s = 800 V/µs. Therefore, option B is correct.
Correct answer: 800 V/µs- A. High power phase control
- B. High power current control
- C. Low power current control
- D. Low power phase control
Explanation: A bidirectional controlled thyristor is intended for high-power AC control, especially phase-control applications such as AC voltage…
Correct answer: High power phase control- A. Vc1 > Vc2 > Vc3 when Ig1 > Ig2 > Ig3.
- B. Vc1 > Vc2 > Vc3 when Ig1 < Ig2 < Ig3.
- C. Vc1 = Vc2 = Vc3 any value of Ig.
- D. Vc1 > Vc2 > Vc3 when Ig1 ≥ Ig2 &Atil
Explanation: Increasing gate current assists thyristor turn-on and reduces its forward breakover voltage. Thus, if Ig1 < Ig2 < Ig3, then Vc1 > Vc2 > Vc3.
Correct answer: Vc1 > Vc2 > Vc3 when Ig1 < Ig2 < Ig3.- A. Forward voltage triggering
- B. Gate triggering
- C. dV / dt triggering
- D. Thermal triggering
Explanation: Gate triggering is the most reliable method because the gate provides deliberate, controlled turn-on with relatively low triggering power.
Correct answer: Gate triggering- A. forward blocking mode
- B. reverse blocking mode
- C. both forward and reverse blocking mode
- D. forward conduction mode
Explanation: A thyristor carries only leakage current in either blocking condition: forward blocking with the anode positive, or reverse blocking with…
Correct answer: both forward and reverse blocking mode- A. Recovery is only 5 µs
- B. Recovery is only 50 µs
- C. Doping is carried out
- D. None of these
Explanation: Fast recovery is obtained by lifetime-control techniques such as doping, but these introduce trade-offs including increased leakage…
Correct answer: Doping is carried out- A. CB
- B. Snubber circuit
- C. Voltage clamping device
- D. Fast acting current limiting device (FACL fuse)
Explanation: A very large, short-duration surge current is limited by a fast-acting current-limiting fuse, which interrupts the fault before the…
Correct answer: Fast acting current limiting device (FACL fuse)- A. of long period
- B. of short duration
- C. both (A) and (B)
- D. neither (A) nor (B)
Explanation: A circuit breaker is relatively slow and is intended to clear sustained or long-duration overcurrent faults.
Correct answer: of long period- A. 20 A
- B. 200 A
- C. 600 A
- D. 400 A
Explanation: A GTO typically requires a negative gate current of roughly 20–25% of its anode current for turn-off.
Correct answer: 200 A- A. CB and fuse.
- B. Heat sink.
- C. Snubber circuit.
- D. Voltage clamping device.
Explanation: Overcurrent protection for an SCR uses series protective devices such as fuses and circuit breakers.
Correct answer: CB and fuse.- A. high value.
- B. low value.
- C. zero value.
- D. moderate value.
Explanation: A voltage-clamping device must draw negligible current during normal voltage, so it presents high impedance.
Correct answer: high value.- A. low
- B. High
- C. moderate
- D. infinity
Explanation: During an overvoltage surge, a clamping device such as a MOV changes to a low-impedance state.
Correct answer: low- A. 100 mA
- B. 500 mA
- C. 1 A
- D. 2 A
Explanation: The latching current of a GTO is generally in the hundreds-of-milliamperes range, and 500 mA is the suitable order among the choices.
Correct answer: 500 mA- A. fast acting fuse
- B. snubber circuit
- C. metal oxide varistor
- D. aluminium block
Explanation: A metal-oxide varistor, or MOV, is a voltage-dependent resistor that remains high-impedance normally and conducts strongly during a…
Correct answer: metal oxide varistor- A. 5 KHz
- B. 10 KHz
- C. 60 KHz
- D. 100 KHz
Explanation: The static induction thyristor, or SITH, is designed for high-speed switching and can operate at frequencies of approximately 100 kHz.
Correct answer: 100 KHz- A. One resistor across the string
- B. Resistors of the same value across each SCR
- C. Resistors of different values across each SCR
- D. One resistor in series with each SCR
Explanation: Equal-value resistors connected across each series SCR share the steady-state voltage nearly equally, compensating for leakage-current…
Correct answer: Resistors of the same value across each SCR- A. RL.
- B. RLC underdamped.
- C. RLC overdamped.
- D. RLC critically damped.
Explanation: Load commutation requires an RLC load whose response is oscillatory, allowing the load current to naturally fall to zero and reverse…
Correct answer: RLC underdamped.