Protection circuit for voltage regulator of vehicle mounted generator

Claim 1

A protection circuit for protecting an output transistor circuit of a semiconductor control device of a vehicle mounted charging generator against an over current flowing through the output transistor circuit due to a short-circuit, which includes a voltage regulator for regulating an output voltage of said generator to a predetermined value by controlling a current flowing through a field winding of said generator, comprising, a first constant voltage source, a first detecting means for detecting a current of an output transistor circuit of said semiconductor control device and providing an output when the current becomes equal to or larger than a normal current of said output transistor circuit, a first capacitor means responsive to the output of said first detecting means to be charged only when the output of said first detecting means exists and discharged when the output of said first detecting means terminates, a first comparator having a reference input supplied with a first constant voltage derived from said first constant voltage source and a comparison input connected to said first capacitor means and adapted to provide a control level output when the voltage of such first capacitor means equals or rises higher than said first constant voltage, and a first diode means connected between an output terminal of said first-comparator and said output transistor circuit to bias said output transistor circuit such that the latter is made non-conductive when said first comparator provides said control output.