Q.

A zener diode with 5 V zener voltage is used to regulate an unregulated dc voltage input of 25 V.  

For a 400 Ω resistor connected in series, the zener current is found to be 4 times load current. The load current (IL) and load resistance (RL) are:      [2025]  

1 IL=20 mA;  RL=250 Ω  
2 IL=10 A;  RL=0.5 Ω  
3 IL=0.02 mA;  RL=250 Ω  
4 IL=10 mA;  RL=500 Ω  

Ans.

(4)

5IL=(25-5)400=120=50 mA

IL=10 mA

5=ILRL

RL=5IL=510×10-3=500 Ω