Example

Question:

The V-I characteristic of a silicon diode is shown in Fig. 14.17. Calculate the resistance of the diode at (a) \( I_D = 15\,\text{mA} \), and (b) \( V_D = -10\,\text{V} \).

Solution:

Considering the diode characteristics as a straight line between \( I = 10\,\text{mA} \) to \( I = 20\,\text{mA} \), passing through the origin:
(a) From the curve, at \( I = 20\,\text{mA}, V = 0.8\,\text{V};\ I = 10\,\text{mA}, V = 0.7\,\text{V} \):
\[ r_f = \frac{\Delta V}{\Delta I} = \frac{0.1\,\text{V}}{10\,\text{mA}} = 10\,\Omega \]
(b) From the curve at \( V = -10\,\text{V}, I = -1\,\mu\text{A} \):
\[ r_{rb} = \frac{10\,\text{V}}{1\,\mu\text{A}} = 1.0 \times 10^7\,\Omega \]