GATE Electrical 2021 | Question: 25

Question

In the circuit shown, a $\text{5 V}$ Zener diode is used to regulate the voltage across load $R_{0}$. The input is an unregulated $DC$ voltage with a minimum value of $\text{6 V}$ and a maximum value of $\text{8 V}$. The value of $R_{S}$ is $6\;\Omega$. The Zener diode has a maximum rated power dissipation of $\text{2.5 W}$. Assuming the Zener diode to be ideal, the minimum value of $R_{0}$ is _________________ $\Omega$.

Answer 1

Given info-

Vz = 5v

V; range 6 to 8v

Rs = 6ohm

Pzmax = 4.5w

Izk = 0 ( Ideal condition)

Rlmin = ?

from ckt

I zmin =I min -I Lmax >= Izk

= (Vimin - Vz)/Rs - Vz/R Lmin >=0

= (6 - 5)/6 - 5/(RLmin) >= 0

1/6 >= 5/(Rlmin)

R Lmin >= 30ohms