In the circuit, both diodes are ideal, the inductance is small and I 00. Which statement is true?

D2 conducts for more than 180° and D1 for 180°.

D1 and D2 each conduct for 180°.

D1 conducts for more than 180° and D2 for 180°.

GATE 2017 EE (EE2) – Question 22

Power Electronics · Single and three-phase configuration of uncontrolled rectifiers · 1 mark · Multiple choice

In the circuit, both diodes are ideal, the inductance is small and $I_0\ne0$. Which statement is true?

Diagram for GATE 2017 EE (EE2) question 22

D1 and D2 each conduct for more than 180°.
D2 conducts for more than 180° and D1 for 180°.
D1 and D2 each conduct for 180°.
D1 conducts for more than 180° and D2 for 180°.

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Show answer and explanation

Correct answer: (A) D1 and D2 each conduct for more than 180°.

Explanation

With zero inductance, the source diode and freewheeling diode would each conduct for half a cycle. A finite source inductance prevents its current from changing instantaneously at a commutation.

Near the positive zero crossing, both diodes conduct while source current rises to I0. Near the negative zero crossing they again overlap while source current falls to zero. Each diode retains its nominal half-cycle plus a commutation-overlap interval.

Thus both conduction angles exceed 180°, **A**.

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