Adjustable Shunt Regulator

This shunt regulator acts like a Zener diode, but we can adjust the voltage (via a potentiometer). Here is the schematic diagram of the circuit:

When the maximum load current is known, then we can choose Rs such as that Rload (at max current) and Rs form a voltage divider that gives a voltage level at slightly higher than the operating voltage. [Source: STMicroelectronics Application Note]