GATE 2025 EE – Question 60
The steady state capacitor current of a conventional DC-DC buck converter, working in CCM, is shown in one switching cycle. If the input voltage is 30 V, the value of the inductor used, in mH, is ____________ (round off to one decimal place).
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Show answer and explanation
Correct answer: 1.79 to 1.81
Explanation
The capacitor current is the inductor ripple current. It crosses zero at 15 μs, which is the middle of the on-time, so $DT=30$ μs, and it crosses zero again at 40 μs, the middle of the off-time, so the off-time is 20 μs and $T=50$ μs. Hence $D=0.6$ and $V_o=DV_{in}=18$ V. The peak-to-peak ripple is $0.2$ A, so $\Delta I=\dfrac{(V_{in}-V_o)DT}{L}$ gives $L=\dfrac{12\times30\times10^{-6}}{0.2}=1.8$ mH.