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GATE 2023 EE – Question 37

Analog and Digital Electronics · Operational amplifiers: characteristics and applications · 2 marks · Multiple choice

Consider the OP AMP based circuit shown in the figure. Ignore the conduction drops of diodes $D_1$ and $D_2$. All the components are ideal and the breakdown voltage of the Zener is 5 V. Which of the following statements is true?

Diagram for GATE 2023 EE question 37
  1. The maximum and minimum values of the output voltage $V_O$ are +15 V and −10 V, respectively.
  2. The maximum and minimum values of the output voltage $V_O$ are +5 V and −15 V, respectively.
  3. The maximum and minimum values of the output voltage $V_O$ are +10 V and −5 V, respectively.
  4. The maximum and minimum values of the output voltage $V_O$ are +5 V and −10 V, respectively.

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Correct answer: (D) The maximum and minimum values of the output voltage $V_O$ are +5 V and −10 V, respectively.

Explanation

The op-amp is an inverting stage with two feedback paths. The path with the 1 kΩ resistor and $D_1$ conducts when the output is negative and gives a gain of $-1$, so for $V_{in}=+10$ V the output reaches $-10$ V (the minimum). For a negative input the output goes positive, and that feedback path passes through the Zener (via $D_2$), which clamps the output at $+5$ V. So the extremes are $+5$ V and $-10$ V.