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 __________.

Fig.

Answer 1

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