Question

In the circuit shown, the ideality factor \( \eta \) of the diode is unity and the voltage drop across it is 0.7 V. The dynamic resistance of the diode at room temperature is approximately:

• A. \(15\ \Omega\)
• B. \(25\ \Omega\)
• C. \(50\ \Omega\)
• D. \(700\ \Omega\)

Hint:

Dynamic resistance of a diode: \( r_d = \frac{V_T}{I_D} \), where \( V_T \approx 25\ \text{mV} \) at room temperature.

Answer 1

The Correct Option is B

Dynamic resistance of a diode is given by: \[ r_d = \dfrac{\eta V_T}{I} \] Where: - \( \eta = 1 \) (ideality factor),
- \( V_T = 25\ \text{mV} = 0.025\ \text{V} \) at room temperature,
- Current \( I = \dfrac{1.7 - 0.7}{1000} = \dfrac{1}{1000} = 1\ \text{mA} \)
So: \[ r_d = \dfrac{0.025}{0.001} = 25\ \Omega \]