GATE EE 2024 Set 1 — Question 35
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Power Electronics → DC-DC Converters → Buck Converter
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Question
A forced commutated thyristorized step-down chopper is shown in the figure. Neglect the ON-state drop across the power devices. Assume that the capacitor is initially charged to 50 V with the polarity shown in the figure. The load current () can be assumed to be constant at 10 A. Initially, is ON and is OFF. The turn-off time available to in microseconds, when is triggered, is_________ (rounded off to the nearest integer).
Correct answer
50 to 50
Solution
In the given voltage-commutated chopper circuit, when the auxiliary thyristor is triggered, the capacitor voltage is applied across the main thyristor in reverse bias. The main thyristor remains reverse biased until the capacitor discharges and recharges in the opposite direction to zero. The circuit turn-off time available to is the time taken for the capacitor to discharge from to under a constant load current .The formula for circuit turn-off time is:Given:
Capacitance
Initial capacitor voltage
Load current Substituting the values:The turn-off time available to is .
Capacitance
Initial capacitor voltage
Load current Substituting the values:The turn-off time available to is .
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