GATE 2019 EC – Question 62
In the circuit shown, $V_s$ is a 10 V square wave of period $T=4$ ms with $R=500\ \Omega$ and $C=10\ \mu$F. The capacitor is initially uncharged at $t=0$, and the diode is assumed to be ideal. The voltage across the capacitor ($V_C$) at 3 ms is equal to ________ volts (rounded off to one decimal place).
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Correct answer: 3.28 to 3.32
Explanation
For $0<t<2$ ms the source is $+10$ V and the diode conducts: $V_C=10\left(1-e^{-t/RC}\right)$ with $RC=5$ ms, so $V_C(2\text{ ms})=10(1-e^{-0.4})=3.3$ V. For $2<t<4$ ms the source is $-10$ V, the diode is reverse biased and the capacitor holds its charge, so $V_C(3\text{ ms})=3.3$ V.