Question

Consider the circuit shown in the figure below:



The Zener diode has a Zener breakdown voltage of $V_Z=10V$ and has the maximum amount of Zener current $I_{Z\left(max\right)}=20mA$. The Zener diode turns on when the voltage of 10 V is applied over it with nearly zero knee current, then the value of load resistance $R_l$, or proper regulation, should be in the range.

• A. $250\Omega =R_L<500\Omega$
• B. $R_L>100\Omega$
• C. $10\Omega =R_L<100\Omega$
• D. $2500\Omega =R_L<500\Omega$

Answer 1

The correct option is A $250\Omega =R_L<500\Omega$

The minimum value of load resistance can be calculated when maximum current flow through the load.
Thus,
Now, $\because$ knee current nearly equal to zero
$\therefore$
$I_{in}=\frac{50-10}{1k\Omega }=40mA$
$\therefore$ $R_{L\left(max\right)=\frac{10}{40}\times {10}^3=\frac{1}{4}\times {10}^3=250\Omega }$
Now for maximum value of load resistance, there should be minimum value of current through the load
$\therefore$
= (40 - 20) × = 20 mA
$\therefore$ $R_L\left(max\right)=\frac{10}{20}\times {10}^3=500\Omega$