26. The SCR remains in the ON state until
A) Gate pulse is removed
B) Anode current drops below holding current
C) Reverse voltage is applied
D) Both B and C
Answer: D) Both B and C
27. The most commonly used material for power semiconductor devices is
A) Germanium
B) Silicon
C) Gallium
D) Graphite
Answer: B) Silicon
28. In an SCR, the anode must be
A) Positive with respect to cathode
B) Negative with respect to cathode
C) Equal to gate voltage
D) Zero
Answer: A) Positive with respect to cathode
29. The forward blocking region of SCR means
A) SCR conducts fully
B) SCR is reverse biased
C) SCR is forward biased but not conducting
D) SCR is open circuit
Answer: C) SCR is forward biased but not conducting
30. When SCR is conducting, its voltage drop is approximately
A) 0.1 V
B) 0.7 V
C) 1–2 V
D) 5–10 V
Answer: C) 1–2 V
31. The main advantage of using power electronics devices is
A) Small size and high efficiency
B) Low speed
C) High cost
D) Complex design
Answer: A) Small size and high efficiency
32. The conduction angle of a half-wave rectifier using SCR varies from
A) 0° to 90°
B) 0° to 180°
C) 90° to 270°
D) 0° to 360°
Answer: B) 0° to 180°
33. The reverse recovery time of a diode is
A) Time taken to turn ON
B) Time taken to turn OFF
C) Time taken to store charge
D) None of these
Answer: B) Time taken to turn OFF
34. The term “firing angle” refers to
A) The angle at which SCR turns ON
B) The conduction time
C) The current waveform
D) The output voltage
Answer: A) The angle at which SCR turns ON
35. The device that can be triggered without a gate signal is
A) SCR
B) DIAC
C) TRIAC
D) BJT
Answer: B) DIAC
36. The turn ON process of SCR is known as
A) Firing
B) Commutation
C) Rectification
D) Inversion
Answer: A) Firing
37. A diode works on the principle of
A) Current amplification
B) Rectification
C) Modulation
D) Inversion
Answer: B) Rectification
38. In a single-phase full converter, the number of SCRs used is
A) 1
B) 2
C) 4
D) 6
Answer: C) 4
39. The purpose of using a heat sink in power electronics is
A) Increase efficiency
B) Reduce current
C) Dissipate heat
D) Increase frequency
Answer: C) Dissipate heat
40. The control terminal of a TRIAC is
A) Source
B) Gate
C) Drain
D) Cathode
Answer: B) Gate
41. The IGBT is a combination of
A) BJT and FET
B) SCR and MOSFET
C) BJT and MOSFET
D) MOSFET and TRIAC
Answer: C) BJT and MOSFET
42. The power MOSFET has
A) High input impedance
B) Low input impedance
C) High output resistance
D) None
Answer: A) High input impedance
43. A chopper operates by
A) Switching the supply ON and OFF
B) Amplifying the signal
C) Converting AC to DC
D) Storing energy
Answer: A) Switching the supply ON and OFF
44. The term PWM stands for
A) Pulse Width Modulation
B) Power Watt Modulation
C) Pulse Waveform Mode
D) Phase Width Mode
Answer: A) Pulse Width Modulation
45. The function of a commutation circuit is to
A) Turn ON SCR
B) Turn OFF SCR
C) Trigger SCR
D) Amplify signal
Answer: B) Turn OFF SCR
46. The frequency of the output of a single-phase inverter is determined by
A) Input voltage
B) Firing angle
C) Switching frequency
D) Load current
Answer: C) Switching frequency
47. A snubber circuit is used to
A) Reduce dv/dt
B) Increase frequency
C) Store energy
D) Reduce harmonics
Answer: A) Reduce dv/dt
48. When the load is inductive, the current
A) Lags voltage
B) Leads voltage
C) Equal to voltage
D) Opposite to voltage
Answer: A) Lags voltage
49. In AC voltage controller, the controlling device is
A) SCR
B) TRIAC
C) DIAC
D) Both A and B
Answer: D) Both A and B
50. The conduction angle of TRIAC can be varied by
A) Changing frequency
B) Changing gate trigger angle
C) Changing load
D) Changing voltage
Answer: B) Changing gate trigger angle
51. The static characteristic of an SCR shows relation between
A) Voltage and current
B) Voltage and power
C) Current and power
D) Voltage and frequency
Answer: A) Voltage and current
52. The turn-on time of SCR is about
A) 1 µs
B) 10 µs
C) 100 µs
D) 1 ms
Answer: B) 10 µs
53. The main disadvantage of TRIAC is
A) Cannot handle high current
B) High cost
C) Unidirectional
D) Requires cooling
Answer: A) Cannot handle high current
54. The basic function of a diode is
A) Amplification
B) Rectification
C) Switching
D) Protection
Answer: B) Rectification
55. SCR can be protected against high dv/dt by
A) Inductor
B) Resistor
C) Capacitor
D) Snubber circuit
Answer: D) Snubber circuit
56. The full-wave rectifier efficiency is approximately
A) 20%
B) 40.6%
C) 81.2%
D) 100%
Answer: C) 81.2%
57. The reverse recovery time of a diode should be
A) Large
B) Small
C) Equal to turn-on time
D) Infinite
Answer: B) Small
58. Power diodes are used in
A) Communication circuits
B) Power control circuits
C) Logic gates
D) Amplifiers
Answer: B) Power control circuits
59. A zener diode is used for
A) Amplification
B) Voltage regulation
C) Switching
D) Current control
Answer: B) Voltage regulation
60. The latching current of an SCR is
A) Minimum current to turn ON SCR
B) Minimum current to keep SCR ON
C) Maximum current of SCR
D) Reverse current
Answer: A) Minimum current to turn ON SCR
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