Question

A zener diode with 5V zener voltage is used to regulate an unregulated dc voltage input of 25V. For a 400 \( \Omega \) resistor connected in series, the zener current is found to be 4 times load current. The load current \( I_L \) and load resistance \( R_L \) are:

• A. \( I_L = 20 \, \text{mA}; \, R_L = 250 \, \Omega \)
• B. \( I_L = 10 \, \text{A}; \, R_L = 0.5 \, \Omega \)
• C. \( I_L = 0.02 \, \text{mA}; \, R_L = 250 \, \Omega \)
• D. \( I_L = 10 \, \text{mA}; \, R_L = 500 \, \Omega \)

Hint:

In zener diode circuits, the load current and load resistance can be found by using Ohm’s law and the given zener voltage.

Answer 1

The Correct Option is D

From the circuit diagram, we have the following: \[ i = \frac{20}{400} \, \text{A} = 10 \, \text{mA} \quad \text{(Load current \( I_L \))} \] \[ V_L = 5V \quad \text{(Zener voltage)} \] Also, \[ R_L = \frac{V_L}{i} = \frac{5}{10 \times 10^{-3}} = 500 \, \Omega \]