Q.

In the given circuit if the power rating of Zener diode is 10 mW, the value of series resistance Rs to regulate the input unregulated supply is             [2024]

1 0.5 kΩ  
2 10 Ω  
3 1 kΩ  
4 10 kΩ  

Ans.

(1)

Potential difference across Rs

V1=8-5=3V

Current through the load resistor

I=51×103=5 mA

Maximum current through Zener diode

Iz max.=105=2 mA

and minimum current through Zener diode

Iz min.=0

∴ Is max.=5+2=7 mA

and Rs min=V1Is max.=37 kΩ

Similarly, Is min.=5 mA

and Rs max.=V1Is min.=35 kΩ

∴ 37 kΩ<Rs<35 kΩ