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ECE Objective Questions { Power Semiconductor Devices and Their Applications }



113. In dc choppers, the waveform for input and output voltages are respectively
A. discontiuous, continuous
B. continuous, discontinuous
C. both continuous
D. both discontinuous

114. In dc choppers, per unit ripple is maximum when duty cycle a is
A.0.2
B.0.5
C.0.7
D.0.8

115. A step.up chopper has Vs as the source voltage and a as the duty cycle. The output voltage for this chopper is given by
A. Vs (1 + a)
B. V5/(1 ? a)
C. V5(1 ? a)
D. V5/(1 + a)

116. In dc choppers if T is the chopping period, then the output voltage can be controlled by PWM by varying
A. T keeping Ton constant
B. Ton keeping T constant
C. T keeping Toff constant
D. Toff keeping T constant

117. In dc choppers, for periodic time T, the output voltage can be controlled by FM by varying
A. T keeping Ton constant
B. Ton keeping T constant
C. Toff keeping T constant
D. T keeping Toff constant

118. A motor armature supplied through phase controlled SCR receives a smoother voltage shape at
A. high motor speed
B. low motor speed
C. rated motor speed
D. very low motor speed

119. An SCR is used to control the speed of a dc motor. At full speed, the motor is taking 1 A at 75 V. The maximum forward surge current rating and maximum forward breakover voltage rating respectively are of the order of
A. 3A, 225V
B. 1A, 300V
C. 6A, 150V
D. 5A, 200V

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