Question

A Zener diode of power rating $1W$ is to be used as a voltage regulator. If Zener diode has a breakdown voltage of $5V$ and it has to regulate voltage which fluctuates between $3V$ and $7V$ , what should be value of $R_{S}$ for safe operation

• A. $10\Omega$
• B. $20\Omega$
• C. $30\Omega$
• D. $40\Omega$

Answer 1

Answer: (A)

$P=1W$
$V_{z}=5V$
$I_{z_{max}}=\frac{P}{V_{Z}}=\frac{1}{5}A$
For safe operation
$R_{s}=\frac{V_{max} - V_{Z}}{I_{Z_{max}}}=\frac{7 - 5}{\left(1 / 5\right)}=10\Omega$