1. The device that can be turned ON by a gate signal but cannot be turned OFF by a gate signal is
A) BJT
B) MOSFET
C) SCR
D) TRIAC
Answer: C) SCR
2. The holding current of an SCR is
A) Less than latching current
B) Greater than latching current
C) Equal to latching current
D) Independent of latching current
Answer: A) Less than latching current
3. In a single-phase half-wave rectifier using an SCR, the conduction angle depends on
A) Load resistance
B) Gate trigger angle
C) Supply frequency
D) Load inductance only
Answer: B) Gate trigger angle
4. The turn-off time of a thyristor depends on
A) Junction temperature
B) Anode current
C) Forward voltage
D) Both A and B
Answer: D) Both A and B
5. A TRIAC conducts current during
A) Only positive half cycle
B) Only negative half cycle
C) Both half cycles
D) None of these
Answer: C) Both half cycles
6. In a step-down chopper, the average output voltage is
A) Directly proportional to duty cycle
B) Inversely proportional to duty cycle
C) Independent of duty cycle
D) Depends on load
Answer: A) Directly proportional to duty cycle
7. The IGBT combines the features of
A) MOSFET and SCR
B) BJT and MOSFET
C) BJT and TRIAC
D) SCR and BJT
Answer: B) BJT and MOSFET
8. The function of a freewheeling diode in a converter is to
A) Reduce ripple
B) Provide a path for inductive current
C) Reduce switching losses
D) Increase efficiency
Answer: B) Provide a path for inductive current
9. In a single-phase full converter, the average output voltage is maximum when firing angle α is
A) 0°
B) 45°
C) 90°
D) 180°
Answer: A) 0°
10. The basic principle of a chopper is
A) Voltage amplification
B) Voltage conversion (DC-DC)
C) Current amplification
D) Frequency conversion
Answer: B) Voltage conversion (DC-DC)
11. Inverters convert
A) DC to AC
B) AC to DC
C) AC to AC
D) DC to DC
Answer: A) DC to AC
12. The most commonly used device in high-frequency applications is
A) SCR
B) TRIAC
C) MOSFET
D) DIAC
Answer: C) MOSFET
13. A cycloconverter converts
A) AC to DC
B) DC to AC
C) AC to AC (variable frequency)
D) DC to DC
Answer: C) AC to AC (variable frequency)
14. The main advantage of power MOSFET over BJT is
A) Low on-state resistance
B) High input impedance
C) High current rating
D) High voltage rating
Answer: B) High input impedance
15. In a controlled rectifier, increasing the firing angle α
A) Increases average DC output
B) Decreases average DC output
C) Has no effect
D) Increases ripple
Answer: B) Decreases average DC output
16. The main disadvantage of SCR is
A) High cost
B) Cannot be turned off by gate signal
C) High leakage current
D) High switching losses
Answer: B) Cannot be turned off by gate signal
17. A DIAC is used for triggering
A) SCR
B) TRIAC
C) IGBT
D) MOSFET
Answer: B) TRIAC
18. Snubber circuits are used in power electronics to
A) Limit dv/dt or di/dt
B) Increase voltage gain
C) Reduce conduction loss
D) Provide isolation
Answer: A) Limit dv/dt or di/dt
19. The main function of a commutation circuit is to
A) Turn on SCR
B) Turn off SCR
C) Reduce harmonics
D) Filter output
Answer: B) Turn off SCR
20. Class D commutation is also known as
A) Voltage commutation
B) Complementary commutation
C) Resonant commutation
D) Load commutation
Answer: D) Load commutation
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