Question

A Zener of power rating $1W$ is to be used as a voltage regulator. If zener has a breakdown of $5V$ and it has to regulate voltage which fluctuated between $3V$ and $7V$, what should be the value of $R_s$ for safe operation (Fig.)?

Answer 1

Given:

$P=1$ watt

Zener breakdown voltage $=5V$

Minimum voltage, $V_{min}=3V$

Maximum voltage, $V_{max}=7V$

As we know,

Current $=I_{Zmax}=\frac{P}{V_z}$

Therefore, by putting the values in the given equation we get,

$I_{Zmax}=\frac{1}{5}=0.2A$

By using $V=IR$

$R_s=\frac{V_{max}-V_{min}}{I_{Zmax}}$

$R_s=\frac{7-3}{0.2}=\frac{4}{0.2}$

$R_s=20\Omega$

$\text{Final Answer}:R_s=20\Omega$