Abstract: A semiconductor switching device is connected in shunt with an A.C. voltage source to be regulated. A modified full-wave bridge rectifier is connected across the voltage source by a first pair of diagonally opposite nodes. A control circuit including a capacitor is connected across the output between a second pair of diagonally opposite nodes of the bridge rectifier to control a gate electrode of the switching device to control the triggering of the switching device in response to the voltage across the bridge rectifier output. The triggering of the switching device regulates the voltage supplied by the voltage source. The bridge rectifier includes an impedance network comprising first and second resistors branching from one of the nodes of the second diagonal pair, each resistor being connected via a diode to a different node of the first diagonal pair.