Question

For a zener regulated power supply, a zener diode with zener voltage $V_z=6.0V$ is used for regulation. The load current is to be $4.0mA$ and the unregulated input $10.0V$. The value of series resistor $R_s$ must be, it $I_Z/I_2=5$

• A. $167\Omega$
• B. $120\Omega$
• C. $250\Omega$
• D. $20\Omega$

Answer 1

Answer: (A)

The value of $R_s$ should be such that the current through the Zener diode is much larger than the load current. This is to have good load regulation. $I_z=20mA$.
The total current through $R_s$ is, therefore, $24mA$.
The voltage drop across $R_s$ is $10.0-6.0=4.0V$.
This gives $R_s=4.0V/\left(24\times 10^{-3}\right)A=167\Omega$