Question

The zener voltage in the circuit shown is \( V_Z = 20 \, V \). The load resistance \( R_L = 5k\Omega \) and the resistance \( R_S = 10k\Omega \). If the input voltage is \( V_S = 100 \, V \), then the current through the zener diode in milliampere is:

• A. 8
• B. 6
• C. 4
• D. 5

Hint:

In Zener regulator, always calculate series current first, then subtract load current to get Zener current.

Answer 1

The Correct Option is C

Step 1: Understand the circuit.
This is a Zener diode voltage regulator circuit.
The Zener diode maintains a constant voltage \( V_Z = 20V \) across the load.

Step 2: Find current through series resistor \( R_S \).
\[ I_S = \frac{V_S - V_Z}{R_S} = \frac{100 - 20}{10k\Omega} = \frac{80}{10000} = 8 \, mA \]

Step 3: Find load current \( I_L \).
\[ I_L = \frac{V_Z}{R_L} = \frac{20}{5k\Omega} = \frac{20}{5000} = 4 \, mA \]

Step 4: Apply current division.
Total current splits into load current and Zener current:
\[ I_Z = I_S - I_L = 8 - 4 = 4 \, mA \]

Step 5: Conclusion.
\[ \boxed{4 \, mA} \]