Voltage regulator for generator of an automobile

Claim 1

A voltage regulator circuit for an AC generator including a field winding for forming a magnetic field and an armature winding in which AC voltages are induced by a magnetic field produced by the field winding, the AC voltages being rectified by a rectifier circuit into a DC voltage to be outputted from the rectifier circuit across output terminals thereof, said voltage regulator circuit comprising: a power transistor coupled in series with a field winding of an AC generator and controlling a supply of excitation current to the field winding by being turned on and off; a voltage divider including a serial connection of resistors coupled across output terminals of a rectifier circuit; a serial connection of a resistor and a control transistor coupled across said output terminals of said rectifier circuit, an emitter and a collector of said control transistor being coupled to one of said output terminals of said rectifier circuit and a terminal of said resistor coupled in series therewith, respectively, and a base of said control transistor being coupled to a junction between the resistors of said voltage divider through a Zener diode having a forward direction opposite to a direction of a base current of said control transistor, wherein the collector of said control transistor is coupled to a base of said power transistor, said control transistor thereby controlling turning on and off of said power transistor; a serial connection of a resistor and a third transistor coupled across said output terminals of said rectifier circuit, a collector of said third transistor being coupled to a terminal of said resistor in series therewith and an emitter of said third transistor being coupled to one of said output terminals of said rectifier circuit which is coupled to the emitter of said control transistor, wherein a base of said third transistor is coupled to the collector of said control transistor; a second Zener diode coupled across the collector and emitter of said third transistor, a forward direction of said second Zener diode being directed opposite to a forward direction of said third transistor across the collector and emitter thereof; a positive feedback circuit, including a serial connection of a resistor and a capacitor, coupled across the collector of said third transistor and the base of said control transistor; and a biasing resistor coupled across the base and emitter of said control transistor.