Question

In a zener regulated power supply a zener diode with Vz = 6 V is used for regulation. The load current is to be 4 mA and the unregulated input is 10 V. What should be the value of series resistor Rs ?

Answer 1

The resistor value $R_{s}$ is 167 ohm.

Solution:

The load current when regulated perfectly must have value of series resistance as R in order that the Zener diode has larger current flow than load current.

The value of series resistance is calculated as follows,

Given:  Zener Voltage, $V_{z}$= 6 V

$I_{c}$= 4 m A

Unregulated input = 10A

$\begin{array}{l}{I_{z}=5 \times 4} \\ {I_{z}=20 \mathrm{m} A}\end{array}$

Now the total current is given by, $I=I_{c}+I_{z}$

I = 20 + 4 = 24 m A

Voltage drop across the series resistance = Unregulated – Regulated  

V = 10 – 6

V = 4 v

Therefore, series resistance $R=\frac{V}{I}$  

$\begin{aligned} R &=\frac{4}{24} m A \\ R &=4 \times \frac{1000}{24} \end{aligned}$

R = 167 ohm.