Question 1 : In a voltage commutated SCR, the main SCR is commutated by
1. triggering the auxiliary SCR
2. sending a negative pulse to the main SCR
3. removing the supply Vs
4. none of the mentioned
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Question 2 : What is the expression for load voltage when the chopper is operated in the second quadrant?
1. Vs
2. E
3. 0
4. E + Ldi/dt
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Question 3 : A voltage commutated chopper has the following parameters:
Vs = 220 V. Commutation circuit: L = 20 μH and C = 50 μF.
Find the turn-off time for the main SCR with a constant load current of 80 A and Ton = 800 μsecs.
1. 137.5 μs
2. 1075 μs
3. 49.67 μs
4. 200 μs
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Question 4 : For a step-up/step-down chopper, if current increases from I₁ to I₂ linearly during T_on, then find the energy stored in the inductor during T_on
1. zero
2. Vs x (I₁ + I₂)
3. Vs x [ (I₁ + I₂)/2 ] x T_on
4. Vs x [ (I₁ + I₂)/2 ] x T
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Question 5 : Type C chopper consists of
1. two diodes and two switches
2. one diode and one switch
3. one diode and three switches
4. three diodes and two switches
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Question 6 : In constant frequency TRC or pulse width modulation scheme, ________ is varied.
1. Vs
2. Ton
3. T
4. f
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Question 7 : For a step-up/step-down chopper, if α (duty cycle) < 0.5 then
1. Vo = Vs
2. Vo < Vs
3. Vo > Vs
4. none of the mentioned
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Question 8 : For a step-up/step-down chopper, if α (duty cycle) = 0.5 then
1. Vo = Vs
2. Vo < Vs
3. Vo > Vs
4. none of the mentioned
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Question 9 : A voltage commutated chopper feeds power to an electric car (battery-powered). The battery voltage is 60 V. The SCR turn-off time is 20 μs. Calculate the value of capacitor (C) required for the commutating circuit.
1. 400 μF
2. 40 nF
3. 40 μF
4. 0.4 mF
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Question 10 : The load commutated chopper circuit consists of
1. two thyristors and one commutating capacitor
2. four thyristors and one commutating capacitor
3. two thyristors and two commutating capacitors
4. four thyristors and two commutating capacitors
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