In the given circuit if the power rating of Zener diode is 10 mW , the value of series resistance R s to regulate the input unregulated supply is:

Step-by-step solution

Potential drop across R s , V 1 = 8 - 5 = 3 V Current through the load resistor I = 5 1 × 10 3 = 5 mA Maximum current through Zener diode I Z , max = 10 5 = 2 mA And minimum current through Zener diode I Z , min = 0 ∴ I S , max = 5 + 2 = 7 m A And R S , min = V 1 I S , max = 3 7 k Ω Similarly, I S , min = 5 mA And R S , max = V 1 I S , min = 3 5 k Ω ∴ 3 7 k Ω < R s < 3 5 k Ω