A general equation for the shunt regulator is derived, giving the relation between the nominal required input voltage and the maximum shunt regulating current for any per unit variation of the input voltage, and for any load. The necessary relation between the shunt regulating current and the output current for maximum electrical efficiency is obtained. It is shown that, for a fixed load, the maximum average efficiency of any shunt regulator is (1 − (k)½)2, wherekis the maximum per unit variation of the voltage to the regulator.