Question

How to calculate a dynamic resistance of a diode(Silicon) if I apply a sinusoidal wave (5V and $\nu =20Hz$) and a resistance of $220\Omega$ is connected serially with a diode ?

• A. 17.2 ohm
• B. 20.4 ohm
• C. 12.5 ohm
• D. 10.8 ohm

Answer 1

The correct option is B 20.4 ohm

The peak value of 5V a.c is:

$=5\times \sqrt{2}=7.07$ d.c Volts
Since in Si diode, the voltage drop = 0.6 V

So, current through diode:
$I=\frac{7.07-0.6}{220}=29.4$ mA
Diode resistance is:
$r=\frac{V}{I}=\frac{0.7V}{0.029}$
$r=20.4$ ohm.