A Zener diode with a breakdown voltage of $V_z=10\text{V}$ is connected in a voltage regulator circuit with a series resistance $R_s=200\Omega$ and a load resistance $R_L=1\text{k}\Omega$. If the input voltage is $V_{in}=15\text{V}$, what is the current through the Zener diode?

Solution

1. Identify the given values: input voltage $V_{in}=15\text{ V}$, Zener voltage $V_z=10\text{ V}$, series resistance $R_s=200\Omega$, and load resistance $$\begin{array}{rl}{R}_L& =1\text{ k}\Omega \\ & =1000\Omega \end{array}$$.
2. Calculate the total current $I$ flowing through the series resistor: $$\begin{array}{rl}I& =\frac{V_{in}-V_z}{R_s}\\ & =\frac{15-10}{200}\\ & =0.025\text{ A}\end{array}$$.
3. Calculate the load current $I_L$ flowing through the load resistor: $$\begin{array}{rl}{I}_L& =\frac{V_z}{R_L}\\ & =\frac{10}{1000}\\ & =0.010\text{ A}\end{array}$$.
4. Determine the Zener current $I_z$ by subtracting the load current from the total current: $$\begin{array}{rl}{I}_z& =I-I_L\\ & =0.025-0.010\\ & =0.015\text{ A}\end{array}$$.
5. Hence the answer is (A).