2. Power Electronics

3. Why Germanium is not used for manufacturing Controlled Rectifiers

4. Why Germanium is not used for manufacturing Controlled Rectifiers
Resistivity of Silicon is 33x102Ωm

5. Why Germanium is not used for manufacturing Controlled Rectifiers
Resistivity of Silicon is 33x102Ωm
Resistivity of Germanium is 0.47Ωm

6. Why Germanium is not used for manufacturing Controlled Rectifiers
Resistivity of Silicon is 33x102Ωm
Resistivity of Germanium is 0.47Ωm
Ge is having very less ability to withstand reverse voltage.

7. Define the following terms:
Latching Current

8. Define the following terms:
Latching Current
Holding Current

9. Define the following terms:
Latching Current
Holding Current
Rate of Rise of Current

10. Define the following terms:
Latching Current
Holding Current
Rate of Rise of Current
Rate of Rise of Voltage

11. Define the following terms:
Latching Current
Holding Current
Rate of Rise of Current
Rate of Rise of Voltage
I2t Rating

12. Define the following terms:
Latching Current
Holding Current
Rate of Rise of Current
Rate of Rise of Voltage
I2t Rating
Reverse Recovery Time

13. Define the following terms:
Latching Current
Holding Current
Rate of Rise of Current
Rate of Rise of Voltage
I2t Rating
Reverse Recovery Time
ITRM

14. Define the following terms:
Latching Current
Holding Current
Rate of Rise of Current
Rate of Rise of Voltage
I2t Rating
Reverse Recovery Time
ITRM
Back Porch Current

15. Define the following terms:
Latching Current
Holding Current
Rate of Rise of Current
Rate of Rise of Voltage
I2t Rating
Reverse Recovery Time
ITRM
Back Porch Current
Pinch off Voltage

16. The moment an SCR starts conducting

17. The moment an SCR starts conducting
A) applied voltage will appear across the device.
B) small amount of current starts flowing through the device.
C) it acts like an open circuited device.
D) it acts like a short circuited device.

18. The moment an SCR starts conducting
A) applied voltage will appear across the device.
B) small amount of current starts flowing through the device.
C) it acts like an open circuited device.
D) it acts like a short circuited device.

19. A SCR can be brought to forward conducting state with gate circuit open when the applied voltage exceeds

20. A SCR can be brought to forward conducting state with gate circuit open when the applied voltage exceeds
A) 1.5V.
B) 2.5V.
C) reverse breakdown voltg.
D) the forward breakover voltage.

21. A SCR can be brought to forward conducting state with gate circuit open when the applied voltage exceeds
A) 1.5V.
B) 2.5V.
C) reverse breakdown voltg.
D) the forward breakover voltage.

22. For a conducting SCR, after removing the Gate pulse, the current through the SCR

23. For a conducting SCR, after removing the Gate pulse, the current through the SCR
A) increases.
B) decreases.
C) remains unchanged.
D) becomes zero.

24. For a conducting SCR, after removing the Gate pulse, the current through the SCR
A) increases.
B) decreases.
C) remains unchanged.
D) becomes zero.

25. Turn-off time of a thyristor affects its

26. Turn-off time of a thyristor affects its
A) operating frequency.
B) thermal behaviour.
C) operating voltage.
D) overload capacity.

27. Turn-off time of a thyristor affects its
A) operating frequency.

28. The value of holding current of an SCR is

29. The value of holding current of an SCR is
A) equal to the value of its latching current
B) slightly less than the value of its latching current
C) slightly more than the value of its latching current
D) equal to the value of its full load current

30. The value of holding current of an SCR is
A) equal to the value of its latching current
B) slightly less than the value of its latching current
C) slightly more than the value of its latching current
D) equal to the value of its full load current

31. A LASCR is a

32. A LASCR is a A) two layer two junction device
B) three layer two junction device
C) four layer two junction device
D) four layer three junction device

33. A LASCR is a A) two layer two junction device
B) three layer two junction device
C) four layer two junction device
D) four layer three junction device

34. A power transistor is turned off effectively by

35. A power transistor is turned off effectively by
A) making base +ve
B) driving the base –ve
C) injecting –ve current at the base
D) removing base voltage

36. A power transistor is turned off effectively by
A) making base +ve
B) driving the base –ve
C) injecting –ve current at the base
D) removing base voltage

37. A diac can be turned ON

38. A diac can be turned ON A) only by the +ve half cycle of the supply.
B) only by the –ve half cycle of the supply.
C) by a +ve pulse.
D) both by +ve as well as –ve half cycles of the supply.

39. A diac can be turned ON A) only by the +ve half cycle of the supply.
B) only by the –ve half cycle of the supply.
C) by a +ve pulse.
D) both by +ve as well as –ve half cycles of the supply.

40. A MOSFET is a

41. A MOSFET is a A) device operating as a switch when overdriven.
B) device requiring large current to turn-on.
C) voltage controlled device.
D)current controlled device.

42. A MOSFET is a A) device operating as a switch when overdriven.
B) device requiring large current to turn-on.
C) voltage controlled device.
D)current controlled device.

43. In the state of saturation a MOSFET acts as

44. In the state of saturation a MOSFET acts as
A) an amplifier.
B) pure resistor.
C) a closed switch.
D) an open switch.

45. In the state of saturation a MOSFET acts as
A) an amplifier.
B) pure resistor.
C) a closed switch.
D) an open switch.

46. A TRIAC can be fired

47. A TRIAC can be fired A) only by the +ve half cycle of the supply.
B) only by the –ve half cycle of the supply.
C) without any biasing.
D) both by +ve as well as –ve half cycles of the supply.

48. A TRIAC can be fired A) only by the +ve half cycle of the supply.
B) only by the –ve half cycle of the supply.
C) without any biasing.
D) both by +ve as well as –ve half cycles of the supply.

49. A SCR can be operated

50. A SCR can be operated A) only in forward biased condition.
B) only in reverse biased condition.
C) in forward & reverse biased condition.
D) without any biasing.

51. A SCR can be operated A) only in forward biased condition.
B) only in reverse biased condition.
C) in forward & reverse biased condition.
D) without any biasing.

52. The semiconductor device which is equivalent to a diode & two resistors is

53. The semiconductor device which is equivalent to a diode & two resistors is
A) UJT
B) SCR
C) TRIAC
D) DIAC

54. The semiconductor device which is equivalent to a diode & two resistors is
A) UJT
B) SCR
C) TRIAC
D) DIAC

55. A Gate turn-off thyristor

56. A Gate turn-off thyristor
A) requires a special turn-off circuit like a thyristor.
B) can be turned-off by removing the gate pulse.
C) can be turned-off by a +ve current pulse at the gate.
D) can be turned-off by a –ve current pulse at the gate.

57. A Gate turn-off thyristor
A) requires a special turn-off circuit like a thyristor.
B) can be turned-off by removing the gate pulse.
C) can be turned-off by a +ve current pulse at the gate.
D) can be turned-off by a –ve current pulse at the gate.

58. SCRs are connected in series to increase the ……. rating of a string.

59. SCRs are connected in series to increase the ……. rating of a string.
A) temperature
B) resistance
C) current
D) voltage

60. SCRs are connected in series to increase the ……. rating of a string.
A) temperature
B) resistance
C) current
D) voltage

61. SCRs are connected in parallel to increase the ……. rating.

62. SCRs are connected in parallel to increase the ……. rating.
A) temperature
B) resistance
C) current
D) voltage

63. SCRs are connected in parallel to increase the ……. rating.
A) temperature
B) resistance
C) current
D) voltage

64. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of

65. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of
A) one resistor across the string
B) resistors of different values across each SCR
C) one resistor in series with the string
D) resistors of the same value across each SCR.

66. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of
A) one resistor across the string
B) resistors of different values across each SCR
C) one resistor in series with the string
D) resistors of the same value across each SCR.

67. For series connected SCRs, dynamic equalising circuit consists of

68. For series connected SCRs, dynamic equalising circuit consists of
A) series R & C circuit but with D across C.
B) series R & C circuit but with D across R.
C) series C & D circuit but with R across C.
D) series R & D circuit but with C across R.

69. For series connected SCRs, dynamic equalising circuit consists of
A) series R & C circuit but with D across C.
B) series R & C circuit but with D across R.
C) series C & D circuit but with R across C.
D) series R & D circuit but with C across R.

70. Thermal runaway of a thyristor occurs because

71. Thermal runaway of a thyristor occurs because
A) if the latching current is more.
B) if the thyristor is loaded with wider current pulses.
C) +ve resistance coefficient of the junction.
D) –ve resistance coefficient of the junction.

72. Thermal runaway of a thyristor occurs because
A) if the latching current is more.
B) if the thyristor is loaded with wider current pulses.
C) +ve resistance coefficient of the junction.
D) –ve resistance coefficient of the junction.

73. In an UJT, with VBB as the voltage across two base terminals, the emitter potential at peak point is given by:

74. In an UJT, with VBB as the voltage across two base terminals, the emitter potential at peak point is given by:
A)  VBB
B) VD
C) VBB + VD
D) VD + VBB

75. In an UJT, with VBB as the voltage across two base terminals, the emitter potential at peak point is given by:
A)  VBB
B) VD
C) VBB + VD
D) VD + VBB

76. A UJT has A) an anode, a cathode & two gates.
B) two anodes & one gate.
C) an anode, a cathode & a gate.
D) two bases & one emitter.

77. A UJT has A) an anode, a cathode & two gates.
B) two anodes & one gate.
C) an anode, a cathode & a gate.
D) two bases & one emitter.

78. A thyristor can be protected against surge currents of long duration by

79. A thyristor can be protected against surge currents of long duration by
A) a thyrector
B) a circuit breaker
C) a fuse
D) an RF filter

80. A thyristor can be protected against surge currents of long duration by
A) a thyrector
B) a circuit breaker
C) a fuse
D) an RF filter

81. .…….. can be used to protect the thyristor against over voltages.

82. .…….. can be used to protect the thyristor against over voltages.
A) a thyrector
B) a circuit breaker
C) a fuse
D) an RF filter

83. .…….. can be used to protect the thyristor against over voltages.
A) a thyrector
B) a circuit breaker
C) a fuse
D) an RF filter

84. Electronic fan speed regulator includes

85. Electronic fan speed regulator includes
A) Wire Wound Resistor
B) Coil
C) SCR & UJT
D) TRIAC & DIAC

86. Electronic fan speed regulator includes
A) Wire Wound Resistor
B) Coil
C) SCR & UJT
D) TRIAC & DIAC

87. To reduce the radio freqency Interference of SCRs …………… may be used.

88. To reduce the radio freqency Interference of SCRs …………… may be used.
A) snubber circuit
B) equalising circuits
C) Butterworth filter
D) an RF filter

89. To reduce the radio freqency Interference of SCRs …………… may be used.
A) snubber circuit
B) equalising circuits
C) Butterworth filter
D) an RF filter

90. Another method for reducing radio interference is

91. Another method for reducing radio interference is
A) time delay circuit
B) zero voltage switching
C) static circuit breaker
D) ac phase control

92. Another method for reducing radio interference is
A) time delay circuit
B) zero voltage switching
C) static circuit breaker
D) ac phase control

93. A thyristor can be protected against large surge currents of short duration by a fast acting

94. A thyristor can be protected against large surge currents of short duration by a fast acting
A) a thyrector
B) a circuit breaker
C) a fuse
D) an RF filter

95. A thyristor can be protected against large surge currents of short duration by a fast acting
A) a thyrector
B) a circuit breaker
C) a fuse
D) an RF filter

96. For parallel connected thyristor string in case of dc circuits the difference in the value of dynamic resistance can be compensated by using

97. For parallel connected thyristor string in case of dc circuits the difference in the value of dynamic resistance can be compensated by using
A) a resistor connected in parallel with each thyristor.
B) a capacitor connected in parallel with each thyristor.
C) an inductor connected in series with each thyristor.
D) a resistor connected in series with each thyristor.

98. For parallel connected thyristor string in case of dc circuits the difference in the value of dynamic resistance can be compensated by using
A) a resistor connected in parallel with each thyristor.
B) a capacitor connected in parallel with each thyristor.
C) an inductor connected in series with each thyristor.
D) a resistor connected in series with each thyristor.

99. Reliability of design of series / parallel connection of more than one thyristors depends mainly on

100. B) turn-on time of each device. C) turn-off time of each device.
Reliability of design of series / parallel connection of more than one thyristors depends mainly on
A) rating of the device.
B) turn-on time of each device.
C) turn-off time of each device.
D) string efficiency of the device.

101. B) turn-on time of each device. C) turn-off time of each device.
Reliability of design of series / parallel connection of more than one thyristors depends mainly on
A) rating of the device.
B) turn-on time of each device.
C) turn-off time of each device.
D) string efficiency of the device.

102. In case of a series string of thyristors the transient voltg
In case of a series string of thyristors the transient voltg. sharing is balanced by using

103. In case of a series string of thyristors the transient voltg
In case of a series string of thyristors the transient voltg. sharing is balanced by using
A) shunt capacitors.
B) balancing resistors.
C) auxiliary thyristors.
D) big inductors.

104. In case of a series string of thyristors the transient voltg
In case of a series string of thyristors the transient voltg. sharing is balanced by using
A) shunt capacitors.
B) balancing resistors.
C) auxiliary thyristors.
D) big inductors.

105. Any Question?