Question

A zener of breakdown voltage VZ = 8 V and maximum Zener current, IZM = 10 mA is subjected to an input voltage Vi = 10 V with series resistance R = 100 Ω. In the given circuit RL represents the variable load resistance. The ratio of maximum and minimum value of RL is __________.

Answer 1

The correct answer is 2

Fig.

Minimum value of RL for which the diode is shorted is
$\frac{R_L}{R_L}$+100×10=8 ⇒RL=400 Ω
For maximum value of RL, current through diode is 10 mA.
So
$i_R= i_{R_L} +I_{ZM}$
$\frac{2}{100}$=$\frac{8}{R_L}$+10×10−3
10×10−3=$\frac{8}{R_L}$
RL = 800 Ω
So
$\frac{R_{Lmax}}{R_{Lmin}}=\frac{800}{400}=2$
So, ratio of maximum and minimum value of RL is 2