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)?

Answer 1

According to the problem, power = 1 W

Zener breakdown voltage, V_z = 5 V

Minimum voltage, V_min = 3 V

Maximum voltage, V_max = 7 V

We know, P = VI

So, current `I_(Z_("max")) = P/V_Z = 1/5` = 0.2 A

For safe operation R_s will be equal to `R_S = (V_("max") - V_Z)/I_(Z_("max"))`

= `(7 - 5)/0.2`

= `2/0.2`

= 10 Ω