Diode Regulator Circuit
The image shows a simple Zener
voltage regulator. It is a shunt regulator and operates by way of the Zener diode's action of maintaining a constant voltage across itself when the current through it is sufficient to take it into the Zener breakdown region.
The resistor R1 supplies the Zener current IZ as well as the load current IR2 (R2 is the load). This regulator is used for very simple low power applications where the currents involved are very small and the load is permanently connected across the Zener
diode (such as voltage reference or voltage source circuits).
Formula Diode Regulator
Once R1 has been calculated, removing R2 will cause the full load current (plus the Zener current) to flow through the diode and may exceed the diode's maximum current rating thereby damaging it. The regulation of this circuit is also not very good because the Zener current (and hence the Zener voltage) will vary depending on VS and inversely depending on the load current.
Zener Diode Voltage Regulator Calculator
Below is a simple to use zener diode voltage regulator calculator. For any given output voltage and current requirement it will calculate the value of power rating of the current limiting resistor and zener diode. Read on to understand how zener diodes and resistors are matched for any particular scenario.
Enter the values for Vout (the desired output voltage - equal to the zener voltage of your diode), Vsource (the maximum power supply voltage - must be at least 2-3 Volts higher than the desired output voltage), and Imax (the maximum current which will be drawn by the load plus a 10% safety buffer).