Question

In a Zener regulated power supply of a Zener diode with $V_2=6V$ is used for regulation. The load current is to be $4mA$ and the unregulated input is $10V$. The value of series resistor $R_S$ is (Assume $I_z=5I_L$):

• A. less than $5$ $\Omega$
• B. Infinite
• C. greater than $100$ $\Omega$
• D. zero

Answer 1

The correct option is C greater than $100$ $\Omega$

Given,

$v_z=6v$

Load current$=4mA=I_L$

unregulated input$=10V$

To find: value of series resistance $R_s=?$

Solution:

$I=I_Z+I_L$

$I_Z=5I_L$ (Given)

$I_Z=5\times 4=20mA$

$I=20+4=24mA$

Voltage drop across $R_s$ is

$V_s=10-6=4V$

Therefore $R_s=\frac{4}{24mA}=167r$

i.e., $R_s$ is greater than $100r$.