GATE 2019 EE – Question 63
In a DC-DC boost converter, the duty ratio is controlled to regulate the output voltage at 48 V. The input DC voltage is 24 V. The output power is 120 W. The switching frequency is 50 kHz. Assume ideal components and a very large output filter capacitor. The converter operates at the boundary of continuous and discontinuous conduction modes. The value of the boost inductor (in $\mu$H) is ________.
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Correct answer: 24
Explanation
$D=1-\frac{V_{in}}{V_o}=0.5$ and the input current is $I_{in}=\frac{120}{24}=5$ A. At the boundary of CCM and DCM the average inductor current is half the peak-to-peak ripple, so $\Delta I=10$ A. From $\Delta I=\frac{V_{in}D}{fL}$, $L=\frac{24\times0.5}{50\times10^3\times10}=24\ \mu$H.