We want to design a simple 5v Zener diode voltage regulator that operates from a source that varies from 10 to 14V. The load current varies from 0 to 10ma. Determine the value of the series resistance so that the minimum magnitude of the Zener diode current is 5ma.

The source is 10-14 V and supply current of 0 to 10ma

The zener voltage should be 5V,

And minimum current of zener 5ma

The resonance of the zener diode is V=IR. Ohms law

5=5E-3R

R=1000ohms. Minimum Resistance.

The current from the source is 10ma,

The zener diode will take 5V, so we connect the zener diode direct to the source

Then, apply ohms law again

V=IR

V=10E-3*1000

V=10V, which is not desirable because we want to design a 5v diode, so we need to place a series resistance that will oppose the flow of current, let imagine the resistance of the resistor is R

Then, apply Kirchoff voltage law.

Voltage from source=Zener voltage + resistor voltage

Therefore,

14=IR+5V

The same current will flow since they are in series, and we want a 5mA current through the zener diode

14-5=5E-3R

9=5E-3R

R=1800ohms.

Then a resistance of 1.8Kohms will be required