GATE 2016 EC (EC3) – Question 49
The Zener I–V curves are shown in Figure I and their series circuit in Figure II. As the supply varies from 0 to 100 V, breakdown occurs in
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Correct answer: (A) D1 only
Explanation
The series diodes must carry the same current. The graph shows D1 has the smaller reverse leakage and an 80 V breakdown, while D2 has larger leakage and a 70 V breakdown.
Before breakdown, most reverse voltage therefore develops across D1. It reaches 80 V and breaks down first. With total supply limited to 100 V, the remaining voltage across D2 is at most about 20 V, below its breakdown.
Thus only **D1, A**, breaks down. Simply choosing the lower individual breakdown voltage would ignore the unequal leakage currents.