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ECE Objective Questions { Power Semiconductor Devices and Their Applications }

64. If firing angle in a SCR rectifier is decreased, output is
A. increased
C. decreased
D. unaffected

65. A SCR is a _____ switch
A. one directional
B. two directional
C. three directional
D. four directional

66.  Comparing a triac & SCR,
A. both are unidirectional devices
B. triac requires more current for turn on than SCR at a particular voltage
C. a tric a has less time for turn off than SCR
D. both are bidirectional devices

67. In a thyristor
A. the turn-off time of a thyristor is less than turn-on time
B. the turn-on time isless turn-off time
C. the turn-off time for the line commutation is less than forced commutation
D. none of the above

68. In a three phase halfwave diode rectifier, the ratio of average output voltage to per phase maximum ac voltage is

69. Each diode in, half wave diode rectifier conducts for
A. 30?
B. 60?

70. In a semi converter, for firing angle less than or equal to 60?, wheeling diode conducts for
A. zero degree
B. 30?
C.(b) 45?
D. 75?

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