1. The turn-on process of an SCR is initiated by
A) Reverse voltage
B) Gate current
C) High temperature
D) Anode voltage increase
Answer: B) Gate current
2. In a single-phase full converter, the average output voltage is maximum when firing angle α =
A) 0°
B) 45°
C) 90°
D) 180°
Answer: A) 0°
3. In an R-L load, the output voltage of a single-phase half-wave controlled rectifier contains
A) Only DC
B) DC and AC
C) Only AC
D) None
Answer: B) DC and AC
4. The reverse recovery time of a diode affects
A) Forward conduction
B) Switching speed
C) Reverse leakage
D) Junction capacitance
Answer: B) Switching speed
5. The device which conducts current in both directions when triggered is
A) SCR
B) TRIAC
C) DIAC
D) MOSFET
Answer: B) TRIAC
6. The forced commutation is generally used in
A) AC circuits
B) DC circuits
C) Both A and B
D) None
Answer: B) DC circuits
7. The gate triggering circuit usually provides
A) Voltage pulse
B) Current pulse
C) Continuous DC
D) Sine wave
Answer: B) Current pulse
8. The snubber circuit in an SCR protects it from
A) Overvoltage
B) Overcurrent
C) High dv/dt
D) Both A and C
Answer: D) Both A and C
9. The voltage across an SCR in forward blocking state is mainly due to
A) Junction capacitance
B) Forward leakage
C) Reverse recovery
D) None
Answer: A) Junction capacitance
10. The function of a free-wheeling diode in a converter is
A) Protect SCR from reverse voltage
B) Provide continuous current in inductive load
C) Reduce voltage ripple
D) Improve efficiency
Answer: B) Provide continuous current in inductive load
11. The average output voltage of a single-phase half-controlled converter is given by
A)
B)
C)
D)
Answer: A)
12. The most suitable commutation method for DC circuits is
A) Natural
B) Line
C) Forced
D) Voltage
Answer: C) Forced
13. In a class D chopper, the output voltage is
A) Positive
B) Negative
C) Both positive and negative
D) Zero
Answer: C) Both positive and negative
14. The inverter converts
A) DC to AC
B) AC to DC
C) DC to DC
D) AC to AC
Answer: A) DC to AC
15. The power factor of a phase-controlled rectifier decreases with
A) Increase in firing angle
B) Decrease in firing angle
C) Increase in load current
D) Increase in supply voltage
Answer: A) Increase in firing angle
16. The main function of a filter in rectifier circuits is
A) To increase ripple
B) To smooth DC output
C) To reduce frequency
D) To increase voltage
Answer: B) To smooth DC output
17. A MOSFET operates in power electronics mainly as a
A) Linear amplifier
B) Current source
C) Switch
D) Voltage regulator
Answer: C) Switch
18. The transfer characteristic of an SCR is
A) Nonlinear
B) Linear
C) Square law
D) Logarithmic
Answer: A) Nonlinear
19. A TRIAC can be triggered by
A) Positive gate current only
B) Negative gate current only
C) Both positive and negative gate currents
D) No gate current
Answer: C) Both positive and negative gate currents
20. The turn-off time of an SCR is the time required for
A) Recombination of charge carriers
B) Forward conduction
C) Gating
D) None
Answer: A) Recombination of charge carriers
21. The commutation circuit that uses capacitor and inductor is called
A) Class A
B) Class B
C) Class C
D) Class D
Answer: B) Class B
22. In a buck converter, the output voltage is always
A) Greater than input
B) Less than input
C) Equal to input
D) Negative
Answer: B) Less than input
23. In a boost converter, the output voltage is
A) Less than input
B) Equal to input
C) Greater than input
D) Zero
Answer: C) Greater than input
24. The ripple frequency of a single-phase full-wave rectifier is
A) Same as supply
B) Twice supply
C) Half supply
D) None
Answer: B) Twice supply
25. The dv/dt protection of SCR is necessary because
A) It causes false triggering
B) It increases turn-off time
C) It damages the device
D) Reduces efficiency
Answer: A) It causes false triggering
26. The conduction losses in MOSFET are due to
A) ON-state resistance
B) Gate charge
C) Drain capacitance
D) Leakage current
Answer: A) ON-state resistance
27. A single-phase full bridge inverter uses
A) 2 SCRs
B) 4 SCRs
C) 6 SCRs
D) 8 SCRs
Answer: B) 4 SCRs
28. The harmonic content in inverter output can be reduced by
A) Increasing frequency
B) Pulse width modulation
C) Increasing load
D) Using filters only
Answer: B) Pulse width modulation
29. A TRIAC can be used for
A) AC voltage control
B) DC chopper
C) Inverter
D) Cycloconverter
Answer: A) AC voltage control
30. The input current in a boost converter is
A) Continuous
B) Discontinuous
C) Constant
D) Zero
Answer: A) Continuous
31. The frequency of output voltage of inverter is controlled by
A) DC voltage
B) Switching frequency
C) Load impedance
D) Filter capacitance
Answer: B) Switching frequency
32. The snubber network typically consists of
A) R and L
B) R and C
C) L and C
D) Only R
Answer: B) R and C
33. The device which can be turned on and off by gate signal is
A) SCR
B) GTO
C) TRIAC
D) BJT
Answer: B) GTO
34. In a full converter with R load, if firing angle = 90°, average output voltage is
A) Positive
B) Zero
C) Negative
D) Maximum
Answer: B) Zero
35. The input power factor of a controlled rectifier is affected mainly by
A) Load current
B) Firing angle
C) Supply voltage
D) Ripple
Answer: B) Firing angle
36. A cycloconverter converts
A) DC to AC
B) AC to DC
C) AC to AC of different frequency
D) DC to DC
Answer: C) AC to AC of different frequency
37. The switching losses in IGBT occur during
A) Steady state
B) Turn ON and Turn OFF
C) Reverse blocking
D) None
Answer: B) Turn ON and Turn OFF
38. For high-frequency applications, the preferred device is
A) SCR
B) MOSFET
C) GTO
D) TRIAC
Answer: B) MOSFET
39. A Class C chopper operates in
A) First and third quadrants
B) Second and fourth quadrants
C) First and fourth quadrants
D) All quadrants
Answer: C) First and fourth quadrants
40. The advantage of IGBT over BJT is
A) Faster switching
B) Lower ON voltage
C) Easier gate control
D) Both A and C
Answer: D) Both A and C
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