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Question
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 Rs for safe operation (Figure)?
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Solution
According to the problem, power = 1 W
Zener breakdown voltage, Vz = 5 V
Minimum voltage, Vmin = 3 V
Maximum voltage, Vmax = 7 V
We know, P = VI
So, current `I_(Z_("max")) = P/V_Z = 1/5` = 0.2 A
For safe operation Rs will be equal to `R_S = (V_("max") - V_Z)/I_(Z_("max"))`
= `(7 - 5)/0.2`
= `2/0.2`
= 10 Ω
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