Get all the Power Semiconductor Devices MCQs that have already been asked in previous Engineering Service Examinations (ESE) papers or this may come in upcoming exams also. So we have arranged almost all previous papers’ MCQs with answers and explanations given here. We will also cover the Special Diodes MCQs also.
Power Semiconductor Devices MCQ
1. Which one of the following devices is not used as the controller in a stabilizer?
- (a) DIAC
- (b) TRIAC
- (c) SCR
- (d) Power Transisitor
2. SCR Turns OFF from conducting state to blocking state on
- (a) reducing gate current
- (b) reversing gate voltage
- (c) reducing anode current below holding current value
- (d) applying A.c. to the gate
3. The below graph depicts
- (a) drain charachteristic of MOSFET
- (b) drain charachteristic of an IGBT
- (c) volt-ampere charachteristic of TRIAC
- (d) volt-ampere charcteristic of an SCR
4. Consider the following statements: A four-layer PNPN device having two gate leads can be turned on by applying a
- positive current pulse to the cathode gate
- positive current pulse to the anode gate
- negative current pulse to the anode gate
- negative current pulse to the cathode gate
which of these statements is/are correct?
- (a) 1 alone
- (b) 1 and 3
- (c) 2 alone
- (d) 2 and 4
5. An SCR triggered by a current pulse through its gate can be turned off by
- (a) giving another pulse of the same polarity to the gate
- (b) by giving a pulse to the cathode
- (c) by giving a pulse to the anode
- (d) by reversing the polarity of the anode and cathode voltage
6. In the forward blocking region of a silicon-controlled rectifier, the SCR is
- (a) In the off-state
- (b) In the on-state
- (c) Reverse biased
- (d) At the point of breakdown
7. Consider the following statements: An SCR, from its OFF state, can be made ON by
- increasing its anode voltage
- increasing its gate current
- decreasing its gate voltage
- decreasing its anode voltage
Which of the statements given above are correct
- (a) Either 1 or 2
- (b) Either 1 or 3
- (c) Either 2 or 4
- (d) Either 3 or 4
8. In an SCR circuit, the anode is grounded. The voltages at the gate and cathode at a particular working condition are measured to be -50V and -55V, respectively. Based on this observation, it could be inferred that
- (a) The SCR is in forward-blocking mode
- (b) The SCR is in forward conducting mode
- (c) The SCR is in reverse blocking mode
- (d) The SCR is damaged
9. An SCR remains turned On if the anode current is more than the
- (a) Break over current
- (b) Trigger current
- (c) Holding current
- (d) Threshold current
10. The di/dt protection for an SCR is achieved through the use of
- (a) R in series with SCR
- (b) RL in series with SCR
- (c) RL across SCR
- (d) L in series with SCR
11. The turn-on time of an SCR is 5 µs. Its trigger pulse should have which one of the following?
- (a) short rise time with pulse width = 2.5 µs
- (b) Long rise time with pulse width = 3 µs
- (c) Short rise time with pulse width = 6 µs
- (d) Short rise time with pulse width = 5 µs
12. Which one of the following devices can not be turned ON or OFF by applying a gate signal?
- (a) SCR
- (b) SCS
- (c) TRIAC
- (d) UJT
13. Which one of the following is not a power MOSFET type?
- (a) Lateral construction (LMOSFET)
- (b) Lateral double diffusion construction (LDMOSFET)
- (c) T construction (TMOSFET)
- (d) Enhancement mode construction (EMOSFET)
14. Consider the following statements.
- In a silicon-controlled rectifier (SCR), if the cathode gate is reverse-biased, then the SCR cannot fire at all.
- The turn-on time of an SCR increases with temperature.
- After an SCR is turned on, it can be made to turn off again by reverse biasing the gate.
- Gate recovery time is the minimum time that the anode voltage must be maintained below holding voltage VH to turn off the SCR.
which of these statements is true?
- (a) 1, 2, 3 and 4
- (b) 1 and 2 only
- (c) 2 and 4 only
- (d) 3 and 4 only
15. Which one of the following statements is correct about SCR?
- (a) SCR is constructed using an NPN and PNP transistor by connecting the base of one transistor to the collector of the other transistor.
- (b) To switch off an SCR, the gate current must be reduced below a certain threshold value.
- (c) Higher levels of gate currents in SCR cause it to conduct at lower anode-to-cathode voltages.
- (d) The higher the gate current in SCR, the higher the holding current to switch off
16. Once an SCR is turned on, it remains so until the anode current goes below
- (a) Trigger current
- (b) Break over current
- (c) Threshold current
- (d) Holding current
17. A freewheeling diode in a phase-controlled rectifier
- (a) improves the line power factor
- (b) is responsible for additional reactive power
- (c) prevents inverse operation
- (d) is responsible for additional harmonics
18. Consider the following statements:
- The speed of operation of MOSFET is more than the speed of operation of SCR
- SCRs have lower power loss than MOSFETs
- The current in conducting state can easily be controlled through the gate in SCR
- MOSFET is not a current-triggered device:
The correct statements are
- (a) 1 and 4 only
- (b) 1 and 2 only
- (c) 2 and 3 only
- (d) 1, 2, 3 and 4
19. An SCR can be turned off
- (a) by passing a negative pulse to its gate
- (b) by removing the gate supply
- (c) by reverse biasing it
- (d) by forcing the current through the gate to become zero
20. Which type of protection is provided for SCR by connecting the snubber circuit across it?
- (a) protection dv/dt
- (b) protection di/dt
- (c) Over-voltage protection
- (d) Over-current protection
21. In a GTO, the anode current begins o fall when the gate current
- (a) is a negative peak at time t = 0
- (b) is a negative peak at time t = storage period
- (c) just begins to become negative at t = 0
- (d) just begins to become positive at t = 0
22. An SCR is turned off when its turn-off time is
- (a) less than the circuit time constant
- (b) greater than the circuit time constant
- (c) less than the circuit turn-off time
- (d) greater than the circuit turn-off time
23. The purpose of connecting a Zener diode in a UJT circuit, used for triggering thyristors, is to
- (a) expedite the generation of triggering pulses
- (b) delay the generation of triggering pulses
- (c) provide a constant voltage to UJT to prevent erratic firing
- (d) provide a variable voltage to UJT as the source voltage changes
24. A freewheeling diode in a phase-controlled rectifier
- (a) improves the line power factor
- (b) enables inverse operation
- (c) is responsible for additional reactive power
- (d) is responsible for additional harmonics
25. In a thyristor, the minimum current required to maintain the device in the ‘ON’ state is called
- (a) Latching current
- (b) Ignition current
- (c) Holding current
- (d) Avalanche current
26. When UJT is used for triggering an SCR, the waveshape of the signal obtained from the UJT circuit is
- (a) Sine wave
- (b) Saw tooth wave
- (c) Trapezoidal wave
- (d) Square wave
27. Which of the following does not cause permanent damage to an SCR?
- (a) High current
- (b) High rate of rise of current
- (c) High-temperature rise
- (d) High rate of rise of voltage
