A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of 5V 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) ?

Explanation

Given, power `= 1W`
Zener breakdown `V_(z) = 5V`
Minimum voltage `V_("min") = 3V`
Maximum voltage `V_("max") = 7V`
Current `I_(Z_("max")) = (P)/(V_(z)) = (1)/(5) = 0.2 A`
The value of `R_(s)` for safe operation `R_(s) = (V_("max") - V_(Z))/(I_(Z_("max"))) = (7 - 5)/(0.2) = (2)/(0.2) = 10 Omega`