Ncert Exercises & Solutions

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

Hint: The rest of the maximum voltage should drop in the external resistance.

Step 1: Find the current in the Zener diode.

Given,

power = 1 W

Zener breakdown V_{z} = 5 V

Minimum voltage V_{\min} = 3 V

Maximum voltage V_{\max} = 7 V

Current I_{Z_{\max}} = \frac{P}{V_{Z}} = \frac{1}{5} = 0.2 A

Step 2: Find the value of the external resistance.

The value of R_{s} for safe operation R_{s} = \frac{V_{\max} - V_{Z}}{I_{Z_{\max}}} = \frac{7 - 5}{0.2} = \frac{2}{0.2} = 10 Ω

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