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GATE 2014 EE (EE2) – Question 33

Analog and Digital Electronics · Simple diode circuits: clipping, clamping, rectifiers · 1 mark · Numerical answer

The sinusoidal AC source shown has rms voltage $20/\sqrt2$ V. Considering every possible R_L, find minimum R_s (Ω) that prevents Zener burnout.

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Correct answer: 299 to 301

Explanation

Assume ideal bridge diodes and a sufficiently large smoothing capacitor. The ac peak is(20/√2)√2=20V. The5V,0.25WZener permits Iz,max=0.25/5=0.05A. Worst case is an open load,so all current flows through it. Rs≥(20−5)/0.05=**300Ω**. Forward drops or ripple would change the actual margin.