TRANSIENT OVER-VOLTAGE PROTECTION CIRCUIT

A transient over-voltage suppressor circuit for a motor vehicle power supply system that includes a diode-rectified alternating current generator. The suppressor circuit comprises a dual coil relay, a Zener diode and a small resistor having a positive temperature coefficient of resistance. The Zener diode and relay coils are connected across the output terminals of a bridge rectifier connected to the generator and when a transient over-voltage occurs the contacts of the relay are closed. When the relay contacts close they connect the resistor and one of the relay coils across the output terminals of the bridge rectifier. The relay contacts open when the resistance of the resistor increases to a predetermined value.