Abstract: A multiple output d.c. to d.c. regulating circuit including an input protection circuit for providing protection against input overcurrent, input transient voltages, sustained input overvoltage and input polarity reversal. The protection circuit powers a d.c. to a.c. inverter which generates high frequency square-wave signals. The square-wave signals are fed to a magnetic saturable reactor regulator which has its controlled windings connected by a rectifying filtering network to a pair of main output terminals and connected by transformer rectifier filter circuits to a plurality of auxiliary output terminals. The d.c. output voltage across the main output terminals is sampled and is compared to a reference voltage of an integrated circuit operational amplifier. The output of the integrated circuit operational amplifier is connected to the control winding of the saturable reactor for controlling the controlled windings so that the square-wave signals are pulse width modulated to regulate the d.c.