Free Power Electronics MCQs with Answers

• A. junction J2 is in reverse bias and J1, J3 is in forward bias.
• B. junction J3 is in forward bias and J1, J2 is in reverse bias.
• C. Junction J1, J3 is in reverse bias and J2 is in forward bias.
• D. Junction J1 and J2 is in forward bias and J3 is in reverse bias.

Explanation: In forward blocking, the outer junctions J1 and J3 are forward biased while the central junction J2 is reverse biased.

• A. junction J2 is in reverse bias and J1, J3 is in forward bias.
• B. junction J3 is in forward bias and J1, J2 in reverse bias.
• C. junction J1, J3 is in reverse bias and J2 is in forward bias.
• D. junction J1 and J2 is in forward bias and J3 is in reverse bias.

Explanation: With reverse voltage applied, J1 and J3 are reverse biased and J2 is forward biased.

• A. It is related to turn off process of the device.
• B. It is related to conduction process of device.
• C. It is related to turn on process of the device.
• D. Both C and D.

Explanation: Latching current concerns the turn-on transition: after the gate pulse is removed, the anode current must rise above this value to latch…

• A. 0.32
• B. 0.67
• C. 0.45
• D. 0.27

Explanation: For an ideal step-up chopper, V_o=V_s/(1-D). Thus D=1-110/150=0.267, approximately 0.27; the larger duty-cycle values would produce much…

• A. 30° to 150°.
• B. 30° to 180°.
• C. 60° to 120°.
• D. 60° to 180°.

Explanation: Current can begin when 400 sin α=200, giving α=30°. It can continue until the source again falls to 200 V at 150°, so the control range is…

• A. RL.
• B. RLC underdamped.
• C. RLC overdamped.
• D. RLC critically damped

Explanation: Load commutation needs the load itself to provide a reverse current or voltage for turning off the thyristor.

• A. it can be turned OFF but not ON with a gate pulse.
• B. it conducts only during one half cycle of an alternating current wave.
• C. it can be turned ON but not OFF with a gate pulse.
• D. it can be turned ON only during one half cycle of an AC.

Explanation: A gate pulse can trigger an SCR into conduction, but removing the gate signal does not turn it off.

• A. 1500 A.
• B. 6000 A.
• C. 2121.32 A.
• D. 4242.64 A.

Explanation: For the same I²t surge-energy limit, doubling the conduction time reduces the allowable current by √2.

• A. Drain, source, gate
• B. Two main terminal and a gate terminal
• C. Cathode, anode, gate
• D. None of the above

Explanation: A TRIAC is a bidirectional thyristor with two main terminals, MT1 and MT2, plus a gate terminal.

• A. PNPN device
• B. A combination of diac and triac
• C. A set of SCRs
• D. A set if SCR,diac and triac

Explanation: A thyristor has four semiconductor layers arranged as P-N-P-N, giving it three junctions.

• A. Diac
• B. Triac
• C. SUS
• D. BCS

Explanation: A BCS, or bilateral controlled switch, is a PNPN-type device controlled through two gates.

• A. Unijunction device
• B. Device with three junction
• C. Device with four junction
• D. None of the above

Explanation: An SCR contains four layers, PNPN, and therefore has three internal PN junctions.

• A. Diac
• B. Triac
• C. Silicon controlled-rectifier SCR
• D. None of above

Explanation: A thyratron is a gas-filled switching tube, and its semiconductor counterpart is the silicon-controlled rectifier, or SCR.