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GATE 2020 EE – Question 40

Analog and Digital Electronics · Simple diode circuits: clipping, clamping, rectifiers · 2 marks · Multiple choice

Consider the diode circuit shown below. The diode, D, obeys the current-voltage characteristic $I_D=I_s\left(\exp\left(\frac{V_D}{nV_T}\right)-1\right)$, where $n>1$, $V_T>0$, $V_D$ is the voltage across the diode and $I_D$ is the current through it. The circuit is biased so that voltage, $V>0$ and current, $I<0$. If you had to design this circuit to transfer maximum power from the current source ($I_1$) to a resistive load (not shown) at the output, what values of $R_1$ and $R_2$ would you choose?

Diagram for GATE 2020 EE question 40
  1. Large $R_1$ and large $R_2$.
  2. Small $R_1$ and small $R_2$.
  3. Large $R_1$ and small $R_2$.
  4. Small $R_1$ and large $R_2$.

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Show answer and explanation

Correct answer: (D) Small $R_1$ and large $R_2$.

Explanation

This is a solar-cell-like source delivering power to the output. $R_1$ is in series with the output, so it should be small to avoid losing power. $R_2$ is in parallel with the source and shunts current away from the load, so it should be large.