The value of the resistor, R S , needed in the DC voltage regulator circuit shown here, equals:

1. $\frac{\left(V_i+V_L\right)}{\left(n+1\right)I_L}$
2. $\frac{\left(V_i-V_L\right)}{n I_L}$
3. $\frac{\left(V_i+V_L\right)}{n I_L}$
4. $\frac{\left(V_i-V_L\right)}{\left(n+1\right)I_L}$

Solution

Across zener diode $V_L=constant$

$\because V_i=V_L+\left(n+1\right)I_L R_S$

$\Rightarrow V_i-V_L=\left(n+1\right)I_L R_S$

$\Rightarrow R_S=\frac{V_i-V_L}{\left(n+1\right)I_L}$

Asked in: JEE Main 2015 (11 Apr Online)

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