In a Zener regulated power supply a Zener diode with `V_(Z) = 6.0 V` is used for regulation. The load current is to be 4.0 mA and the unregulated input is 10.0 V. What should be the value of seriesresistor `R_(S)` ? Choose zener current to be 20 mA.

Options

A. `163 Omega`
B. `167 Omega`
C. `175 Omega`
D. `186 Omega`

Answer

B

Explanation

The value of `R_(S)` should be such that the current through the Zener diode is much larger than the load current. This is to have good load regulation. Choose Zener current as five times the load current, i.e., `I_(Z) = 20 mA`. The total current through `R_(S)` is, therefore, 24 mA. The voltage drop across `R_(S)` is `10.0-6.0 = 4.0V`.
This gives `R_(S) = 4.0V//(24 xx 10^(-3)) A = 167 Omega`.