GATE 2024 EE – Question 35
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 ($I_L$) can be assumed to be constant at 10 A. Initially, $\text{Th}_M$ is ON and $\text{Th}_A$ is OFF. The turn-off time available to $\text{Th}_M$ in microseconds, when $\text{Th}_A$ is triggered, is __________ (rounded off to the nearest integer).
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Correct answer: 50
Explanation
When $\text{Th}_A$ is triggered, the constant load current discharges and then reverses the 50 V capacitor, and $\text{Th}_M$ is reverse biased until the capacitor voltage returns to zero. With a constant current $I_L$, $t=\dfrac{CV}{I_L}=\dfrac{10\ \mu\text{F}\times50}{10}=50\ \mu$s.