In resonant converters, switching occurs at

 41. The turn-off time of an SCR depends mainly on

A) Load current
B) Junction temperature
C) Circuit inductance
D) Supply frequency
Answer: B) Junction temperature

---

42. A Class-D chopper is also known as

A) Two-quadrant chopper
B) Four-quadrant chopper
C) Step-up chopper
D) Step-down chopper
Answer: B) Four-quadrant chopper

---

43. In an SCR, the gate signal is applied at

A) Anode-cathode junction
B) Cathode-base junction
C) Gate-cathode junction
D) Anode-gate junction
Answer: C) Gate-cathode junction

---

44. The forward voltage drop across a conducting SCR is typically

A) 0.1–0.3 V
B) 0.7–1.0 V
C) 1–2 V
D) 3–5 V
Answer: C) 1–2 V

---

45. The device that can be triggered by both positive and negative gate signals is

A) SCR
B) TRIAC
C) DIAC
D) GTO
Answer: B) TRIAC

---

46. The average output voltage of a single-phase full converter with firing angle α is

A) $V_{avg} = \frac{Vm}{\pi}\cos\alpha$
B) $V_{avg} = \frac{Vm}{2\pi}\cos\alpha$
C) $V_{avg} = \frac{Vm}{\pi}(1+\cos\alpha)$
D) $V_{avg} = Vm\cos\alpha$
Answer: A) $V_{avg} = \frac{Vm}{\pi}\cos\alpha$

---

47. The freewheeling diode in a converter helps to

A) Reduce voltage stress
B) Reduce current ripple
C) Maintain load current continuity
D) Increase efficiency
Answer: C) Maintain load current continuity

---

48. The power factor of a fully controlled converter is

A) Unity
B) Lagging
C) Leading
D) Zero
Answer: B) Lagging

---

49. The output frequency of a single-phase full-bridge inverter is determined by

A) Switching frequency
B) Firing angle
C) Supply frequency
D) Load impedance
Answer: A) Switching frequency

---

50. The turn-on time of a MOSFET is mainly limited by

A) Gate capacitance
B) Drain current
C) Source voltage
D) Threshold voltage
Answer: A) Gate capacitance

---

51. The IGBT combines the features of

A) SCR and BJT
B) MOSFET and BJT
C) SCR and MOSFET
D) UJT and BJT
Answer: B) MOSFET and BJT

---

52. In PWM inverters, the modulation index determines

A) Output voltage
B) Frequency
C) Power factor
D) Duty cycle
Answer: A) Output voltage

---

53. In a 3-phase inverter, the line-to-line RMS output voltage is

A) $\frac{Vm}{\sqrt{2}}$
B) $\frac{Vm}{\sqrt{3}}$
C) $0.612 \times Vdc$
D) $0.707 \times Vdc$
Answer: C) $0.612 \times Vdc$

---

54. In a buck converter, the output voltage ripple decreases with

A) Higher inductance
B) Lower capacitance
C) Higher duty ratio
D) Lower switching frequency
Answer: A) Higher inductance

---

55. The major loss in a power MOSFET during switching is

A) Conduction loss
B) Gate drive loss
C) Overlap loss
D) Snubber loss
Answer: C) Overlap loss

---

56. The device that cannot block reverse voltage is

A) SCR
B) GTO
C) TRIAC
D) MOSFET
Answer: D) MOSFET

---

57. In a three-phase inverter, each switch conducts for

A) 60°
B) 90°
C) 120°
D) 180°
Answer: C) 120°

---

58. The function of RC snubber circuit is

A) To protect against high dv/dt
B) To increase current
C) To limit di/dt
D) To decrease switching frequency
Answer: A) To protect against high dv/dt

---

59. The safe operating area (SOA) of IGBT is limited by

A) Current and voltage
B) Frequency
C) Inductance
D) Load resistance
Answer: A) Current and voltage

---

60. A DIAC is mainly used for triggering

A) GTO
B) TRIAC
C) SCR
D) BJT
Answer: B) TRIAC

---

61. The firing angle control in AC regulators controls

A) RMS voltage
B) Frequency
C) Current phase
D) Load resistance
Answer: A) RMS voltage

---

62. In a converter, overlap angle depends on

A) Source inductance
B) Load resistance
C) Firing angle
D) Supply frequency
Answer: A) Source inductance

---

63. The voltage regulation in DC-DC converters can be improved by

A) Feedback control
B) Reducing frequency
C) Increasing inductance
D) Increasing capacitance
Answer: A) Feedback control

---

64. A cycloconverter operates efficiently for

A) High frequency
B) Low frequency
C) Constant voltage
D) DC supply
Answer: B) Low frequency

---

65. The main function of commutation circuit in a thyristor is

A) Turn-off
B) Turn-on
C) Increase power
D) Reduce voltage ripple
Answer: A) Turn-off

---

66. The dv/dt rating of SCR is typically in the range of

A) 1–10 V/µs
B) 10–500 V/µs
C) 1–5 kV/µs
D) 1–10 mV/µs
Answer: B) 10–500 V/µs

---

67. The conduction losses in power semiconductor devices depend mainly on

A) On-state voltage drop
B) Switching speed
C) Load inductance
D) Supply voltage
Answer: A) On-state voltage drop

---

68. In a single-phase inverter, dead time is used to

A) Prevent short-circuiting the DC link
B) Increase voltage
C) Reduce harmonics
D) Increase current
Answer: A) Prevent short-circuiting the DC link

---

69. The operation of SCR in inverter mode is called

A) Rectification
B) Regeneration
C) Commutation
D) Inversion
Answer: D) Inversion

---

70. The power factor of a converter decreases with

A) Increased firing angle
B) Decreased firing angle
C) Increased load resistance
D) Decreased source voltage
Answer: A) Increased firing angle

---

71. The turn-on losses in IGBTs are generally

A) Less than turn-off losses
B) Greater than turn-off losses
C) Equal to turn-off losses
D) Negligible
Answer: A) Less than turn-off losses

---

72. The harmonic order in a 6-pulse converter is

A) 6n ± 1
B) 12n ± 1
C) 3n ± 1
D) n
Answer: A) 6n ± 1

---

73. The commutation method used in high-frequency inverters is

A) Load commutation
B) Resonant commutation
C) Line commutation
D) Natural commutation
Answer: B) Resonant commutation

---

74. The safe turn-off time of SCR is

A) Greater than circuit turn-off time
B) Less than circuit turn-off time
C) Equal to circuit turn-off time
D) Independent of circuit
Answer: B) Less than circuit turn-off time

---

75. The switching losses are negligible in

A) Hard-switched converters
B) Resonant converters
C) PWM inverters
D) Line-commutated converters
Answer: B) Resonant converters

---

76. The peak inverse voltage (PIV) of a single-phase full converter is

A) Vm
B) 2Vm
C) 3Vm
D) 4Vm
Answer: B) 2Vm

---

77. A thyristor conducts when

A) Forward biased and gate signal applied
B) Reverse biased
C) Forward biased only
D) Gate signal only
Answer: A) Forward biased and gate signal applied

---

78. The dynamic characteristics of an SCR are measured using

A) Double pulse test
B) RLC circuit
C) CRO
D) Pulse transformer
Answer: A) Double pulse test

---

79. The current chopping in an SCR occurs when

A) Load current falls below holding current
B) Gate signal removed
C) Voltage reversed
D) Frequency increased
Answer: A) Load current falls below holding current

---

80. The device best suited for AC voltage control is

A) MOSFET
B) TRIAC
C) GTO
D) IGBT
Answer: B) TRIAC

---

81. The conduction angle in a 3-phase full converter is

A) 120°
B) 180°
C) 240°
D) 300°
Answer: B) 180°

---

82. The instantaneous power in a purely resistive load is always

A) Positive
B) Negative
C) Zero
D) Alternating
Answer: A) Positive

---

83. The RMS value of output voltage of a single-phase half-wave converter is

A) $\frac{Vm}{2}$
B) $\frac{Vm}{\sqrt{2}}$
C) $\frac{Vm}{\pi}$
D) $\frac{Vm}{2\sqrt{2}}$
Answer: A) $\frac{Vm}{2}$

---

84. The SCR can be turned on by

A) Increasing anode voltage
B) Gate current
C) Reverse voltage
D) Reducing temperature
Answer: B) Gate current

---

85. The speed control of DC motor using converter is achieved by

A) Varying α
B) Varying frequency
C) Changing armature resistance
D) Changing polarity
Answer: A) Varying α

---

86. In inverter mode, the firing angle of converter is

A) 0–90°
B) 90–180°
C) 180–270°
D) 270–360°
Answer: B) 90–180°

---

87. The current through a freewheeling diode flows when

A) Load is inductive
B) Load is resistive
C) Load current is zero
D) Gate pulse is removed
Answer: A) Load is inductive

---

88. The voltage control in inverters is commonly done by

A) PWM
B) Firing angle
C) Series resistance
D) Frequency
Answer: A) PWM

---

89. In a chopper, the frequency of output ripple can be reduced by

A) Increasing switching frequency
B) Decreasing switching frequency
C) Increasing load resistance
D) Increasing duty cycle
Answer: A) Increasing switching frequency

---

90. In a full converter, if α = 180°, the output voltage is

A) Maximum positive
B) Zero
C) Maximum negative
D) Half
Answer: B) Zero

---

91. The storage time in BJT affects

A) Turn-off speed
B) Turn-on speed
C) Gain
D) Voltage
Answer: A) Turn-off speed

---

92. The ideal switch has

A) Zero on-state resistance and infinite off resistance
B) Finite resistance in both states
C) Zero off resistance
D) High leakage current
Answer: A) Zero on-state resistance and infinite off resistance

---

93. The power loss during turn-off of IGBT is due to

A) Tail current
B) Gate resistance
C) Leakage
D) dv/dt
Answer: A) Tail current

---

94. In resonant converters, switching occurs at

A) Zero voltage or current
B) Peak voltage
C) Peak current
D) Fixed power
Answer: A) Zero voltage or current

---

95. The voltage across SCR during reverse blocking mode is supported by

A) Junction J1 and J3
B) Junction J2
C) Junction J1 only
D) All junctions
Answer: A) Junction J1 and J3

---

96. The trigger circuit of an SCR must provide

A) Proper timing and amplitude
B) High current
C) Reverse polarity
D) Continuous signal
Answer: A) Proper timing and amplitude

---

97. In a 3-phase inverter, the lowest harmonic order is

A) 3
B) 5
C) 7
D) 11
Answer: B) 5

---

98. The maximum efficiency of a converter is achieved when

A) Losses are minimum
B) α = 0°
C) α = 90°
D) α = 180°
Answer: A) Losses are minimum

---

99. The SCR can be protected from overcurrent by

A) Fuse or circuit breaker
B) Snubber
C) RC circuit
D) Gate resistance
Answer: A) Fuse or circuit breaker

---

100. In high-frequency inverters, the main advantage is

A) Smaller filter size
B) Lower losses
C) Higher current
D) Larger transformer
Answer: A) Smaller filter size