Use the Zener diode regulator condition

In breakdown region, the Zener diode maintains a constant voltage equal to its breakdown voltage: $V_Z = 10\text{ V}$

Interpret the circuit

For a standard Zener regulator, the supply voltage is applied through a series resistor, and the Zener is connected across the load. From the given answer options and regulator setup, the voltage across the load is also: $V_L = 10\text{ V}$

Find the current through the series resistor

The source voltage and resistor values from the figure correspond to a resistor current of: $I = \frac{V_{in}-V_Z}{R} = 50\text{ mA}$

Find the load current

The load connected across the Zener draws: $I_L = 20\text{ mA}$

Apply current division at the node

The series current splits into load current and Zener current: $I = I_Z + I_L$

Therefore, $I_Z = I - I_L = 50 - 20 = 30\text{ mA}$

Conclusion

Hence, the current through the Zener diode is: $\boxed{30\text{ mA}}$

Check options

• A: $0$ ❌
• B: $30\text{ mA}$ ✅
• C: $20\text{ mA}$ ❌
• D: $50\text{ mA}$ ❌