1. In a flyback converter, the inductor of the buck-boost converter has been
replaced by a
Correct : C. Flyback transformer
2. For bidirectional operation of converters
Correct : A. A parallel combination of controllable switch and a diode is used
3. For a buck converter to reduce the conduction losses in diode
Correct : B. A low on - resistance switch can be added in parallel
4. A step - down choppers can be used in
Correct : D. All of these
5. The output current in PWM DC - DC converters is equal to
Correct : C. Either (a) or (b)
6. Advantages of Cuk converter is / are
Correct : D. None of these
7. In a push - pull converter, the filter capacitor can be obtained as
Correct : C. Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 )
8. The control method used for PWM dc - dc converter is
Correct : D. All of these
9. The control method used for PWM dc - dc converter is
Correct : B. Current mode control
10. In current commutated DC-DC choppers, the voltage spike appears across
the load when
Correct : C. Both (a) and (b)
11. In a load commutated DC - DC chopper, the capacitor has a
Correct : C. Symmetric trapezoidal voltage across itself
12. Voltage commutation circuit can be converted into a current commutation
by interchanging the positions of
Correct : A. Diode and capacitor
13. During the commutation period in 3 phase converter, overlap time is
Correct : C. Dependent on both the load current and load voltage behind the short circuit current
14. In a three phase converter, the number of notches per cycle is
Correct : C. Six
15. Unipolar modulation is generally used in
Correct : D. DC - DC converters
16. Very large values of modulation index (greater than 3.24) lead to
Correct : A. Square AC output voltage
17. With increase in firing angle
Correct : B. Harmonic distortion increases and quality of input current decreases
18. The advantage of using free - wheeling diode in half controlled bridge
converter is that
Correct : A. There is always a path for the dc current independent of the ac line
19. The input current waveform of a bridge controlled rectifier when the load is
perfectly filtered is
Correct : B. Square wave
20. A full wave rectifier with resistive load produces
Correct : D. Do not produce harmonics
21. If all the SCR’s of 3 phase PAC is replaced by diodes, they would be
triggered
Correct : B. 60 degree after the zero crossing of the corresponding line voltages
22. An RC snubber network used in BJT
Correct : D. All of these
23. In a 3 phase half wave rectifier, when firing angle is less than 90 degree,
then the average dc output voltage becomes
Correct : A. Positive
24. In dual converters,
Correct : A. Both rectifiers provides positive current to the load
25. A single phase ac - dc converter is also known as
Correct : A. rectifier
26. In ac - dc conversion, when the switch is closed then the sum of voltages
around the loop is
Correct : B. Non zero
27. Choppers are used to control the DC voltage level.
Correct : A. True
28. Cuk-converter is better than Buck converter in terms of the output voltage.
Correct : A. True
29. What is the formula for output voltage for Buck converter?
Correct : D. D×Vin
30. What is the formula for output voltage for Buck-Boost converter?
Correct : C. D×Vin ÷ (1
31. What is the formula for output voltage for Boost converter?
Correct : D. D×Vin
32. Buck-Boost acts as Buck converter for duty cycle is equal to _________
Correct : D. .4
33. Buck-Boost acts as Boost converter for duty cycle is equal to _________
Correct : A. .8
34. Inductor and Capacitor in Buck converter are used to ___________
Correct : C. Filter out the harmonics
35. Calculate the output voltage of the Buck converter if the supply voltage is
789 V and duty cycle value is .9.
Correct : B. 710.1 V
36. Calculate the output voltage of the Boost converter if the supply voltage is
156 V and duty cycle value is .4.
Correct : A. 260 V
37. Under harmonic free load voltages, the 3 phase VSI
Correct : A. Does not contains second harmonic
38. A fully controlled converter uses
Correct : B. thyristors only
39. In a B-2 type full controlled bridge converter
Correct : B. two SCRs conduct at a time
40. In a step down chopper, if Vs = 100 V and the chopper is operated at a duty
cycle of 75 %. Find the output voltage.
Correct : B. 75 V
41. Find the expression for output voltage for a step-up chopper, assume linear
variation of load current and α as the duty cycle.
Correct : C. Vs/(1-α)
42. Find the output voltage for a step-up chopper when it is operated at a duty
cycle of 50 % and Vs = 240 V.
Correct : B. 480 V
43. In the method of phase control, the phase relationship between ___ & ___ is
controlled by varying the firing angle
Correct : C. start of the load current, start of the load voltage
44. In a single phase half-wave thyristor circuit with R load & Vs=Vm sinωt,
the maximum value of the load current can be given by
Correct : C. Vm/2
45. A single-phase half-wave thyristor circuit with R load is triggered at an
angle of α = 0°. As such, the maximum value of the average output voltage would be given by Consider Vs = Vm sinωt.
Correct : C. Vm/π
46. The AC voltage controllers are used in __________ applications.
Correct : B. electric heating
47. A cycloconverter is a:
Correct : D. Either a or c
48. IGT stands for
Correct : B. Insulated gate bidirectional transistor
49. Number of PN junction in an SCR is
Correct : B. Three
50. In a silicon controlled rectifier, the load is connected
Correct : B. In series with anode
51. Anode of an operational SCR is
Correct : A. Always positive w.r.t cathode
52. If the gate voltage of an SCR is removed, then the
Correct : B. anode current does not decrease at all
53. In a single phase full wave rectifier, during blocking state the peak inverse
voltage of diode is
Correct : B. 2 V m
54. In a full wave rectifier, the rectification ratio is approximately equal to
Correct : C. 81%
55. For power output higher than 15 kW, the suitable rectifier is
Correct : D. Only (b) and (c)
56. The sum of all phase current in a star connected primary winding with no
neutral connection is equal to
Correct : D. Zero at all times
57. In a 3 phase bridge rectifier the ripple frequency is
Correct : D. Six times the input frequency
58. DIAC are specifically designed to trigger
Correct : D. Only (a) and (b)
59. As the breakdown voltage reached, the DIAC exhibits
Correct : D. All of these
60. In BJT, the forward biased base emitter junction inject holes from base to
emitter, the holes
Correct : D. Only (a) and (b)
61. In BJT, switching losses occurs
Correct : C. Both at turn on and off
62. Choppers is a
Correct : D. DC - DC converters
63. The average value of the output voltage in a step - down dc chopper is given
by
Correct : B. V 0 = D V s
64. The voltage will be
Correct : D. 325 V
65. The dc current will be approximately
Correct : B. 3 A
66. The ac input current at slip rings will be
Correct : C. 4.1A
67. For 3 phase rotary converters, when power factor is unity. the ac line to dc
current ratio is
Correct : D. 0.942.
68. In an arc rectifier the drop in voltage at the cathode is approximately
Correct : B. 6 to 7 volts
69. In arc rectifiers mercury is chosen as the liquid for rectifier because
Correct : D. all of the above.
70. Ionization potential of mercury is approximately
Correct : C. 10.4 V
71. Least undulating current will be delivered by which mercury arc rectifier
Correct : D. 6 phase.
72. In a mercury arc rectifier the cathode voltage drop is due to
Correct : B. expenditure of energy in liberating electrons from the mercury
73. In mercury arc rectifier, voltage drop at anode is due to
Correct : A. energy spent in overcoming the electrostatic field
74. The average life of the glass bulb rectifier is
Correct : C. 10,000 to 15,000 hours
75. The vacuum inside the glass bulb of a mercury arc rectifier is of the order of
Correct : C. 5 x 10-5 cm of Hg
76. For mercury arc rectifiers, the anode is usually made of
Correct : D. Graphite.
77. In a phase controlled 3 phase ac voltage controller, the harmonic present is
Correct : B. 3
78. The maximum firing angle in the half wave controlled regulator is
Correct : A. 180 degree
79. The on - state voltage drop of IGBT consists of
Correct : D. All of these
80. To detect an over - current fault condition, the most reliable method is to
connect a
Correct : D. Voltage sensor in series with IGBT
81. The IGBT resulted in higher switching speed and lower energy losses. It can
be used for
Correct : C. Constant voltage and frequency power supplies
82. An ideal diode is
Correct : D. Only (a) and (c)
83. Bidirectional semiconductor device is
Correct : D. TRIAC
84. With gate open, the maximum anode current at which SCR is turned off
from ON condition is called
Correct : D. latching current
85. The curve between V and I of SCR when anode is positive w.r.t cathode and
when anode is negative w.r.t cathode are known as
Correct : C. former as forward characteristics and later as reverse characteristics
86. Form factor of a rectifier is the ratio of
Correct : C. Average value of current and voltage to its root mean square value
87. Ripple factor is the ratio of
Correct : B. Average value of the ac component of load voltage to the peak value of voltage
88. Transformer utilization factor is a measure of the merit of a rectifier circuit.
It is the ratio of
Correct : C. DC output power to the transformer volt - amp rating required by secondary
89. Which of the following finds application in speed control of a dc motor?
Correct : A. FET
90. In mercury arc rectifiers the voltage drop in arc is nearly
Correct : C. 10 volts per centimeter of arc length
91. A cycloconverter is a _________
Correct : C. one stage frequency converter
92. Applications of cycloconverters include
Correct : D. all of the mentioned
93. The single phase mid-point type cycloconverter uses __________ number of
SCRs.
Correct : A. 4
94. The single phase bridge type cycloconverter uses __________ number of
SCRs.
Correct : A. 4
95. The principle of three phase cycloconverter is to
Correct : B. vary progressively the firing angle of the devices
96. In three phase cycloconverters, the reduction factor is given by
Correct : B. (input frequency/output frequency) -1
97. In a three phase half-wave cycloconverter ___________
Correct : A. both inverting and converting action takes place
98. In the ___________ type of chopper, two stage conversions takes place.