In a Zener regulator, the d.c. input is 10V ± 20%. The output requirements are 5 V, 20 mA. Assume Iz(min) and Iz(max) as 5 mA and 80A. Design the Zener regulator.

Question

In a Zener regulator, the d.c. input is 10V ± 20%. The output requirements are 5 V, 20 mA. Assume [latex]I_{z(min)}[/latex] and [latex]I_{z(max)}[/latex] as 5 mA and 80A. Design the Zener regulator.

Accepted Answer

The minimum Zener current is [latex]I_{z (min)}[/latex] = 5 mA when the input voltage is minimum. Here the input voltage varies between 10 V ± 20% i.e. 8 V and 12 V.
Therefore, the input voltage [latex]V_{i(min)}[/latex] = 8 V
Given load current [latex]I_{L}[/latex] = 20 mA and the voltage across the load, [latex]V_{0}[/latex] = 5 V.
Therefore,

[latex]R_{L} =\frac{V0}{I_L}=\frac{5\,V}{20 × 10^{– 3}}[/latex]= 250 Ω

Hence, the series resistance

R =[latex]\frac{V_{i(min)} – V_{0}}{(I_{z(min)} + I_{L})}[/latex]

= [latex]\frac{(8 – 5)}{(5 + 20) × 10^{– 3}}[/latex] = 120 Ω

The various values are given in the Zener regulator shown in Fig. 18.20.

Question 18.32: In a Zener regulator, the d.c. input is 10V ± 20%. The outpu...

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