The GATE Grind

GATE 2018 EE – Question 13

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

A single phase fully controlled rectifier is supplying a load with an anti-parallel diode as shown in the figure. All switches and diodes are ideal. Which one of the following is true for instantaneous load voltage and current?

Diagram for GATE 2018 EE question 13
  1. $v_o\ge0$ & $i_o<0$
  2. $v_o<0$ & $i_o<0$
  3. $v_o\ge0$ & $i_o\ge0$
  4. $v_o<0$ & $i_o\ge0$

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Show answer and explanation

Correct answer: (C) $v_o\ge0$ & $i_o\ge0$

Explanation

The anti-parallel (freewheeling) diode clamps the output voltage at zero whenever it would go negative, so $v_o\ge0$. The load current flows only in the direction allowed by the thyristors and the diode, so $i_o\ge0$.