Fault indicator light control circuit

摘要

A fault indicator light control circuit for a regulator controlled alternator/battery charging system has a first transistor connected with a light bulb in its conductive path to be turned "ON" when the transistor is conducting. Conduction of the transistor is controlled by a plurality of conductive paths connected to the base of the transistor and each path includes a Zener diode having a breakdown voltage substantially above the rated voltage of the battery. The conductive paths are connected to detect any one of a plurality of circuit operating defects, including a short in the silicon controlled rectifier (SCR) of a solid state regulator, an open SCR and a regulator failure. A capacitor is connected in the circuit to be charged by an alternator voltage having a polarity opposite that which is used to charge the battery. The capacitor voltage is used as a reference to bias the first transistor "OFF" when the system is operating normally. A second transistor includes another Zener diode connected to the base thereof and is selected to have a breakdown level substantially lower than that of the other Zener diodes used in the circuit. The second transistor is connected to bias the first transistor "OFF" immediately when the circuit is operating normally but an open circuit is detected between the regulator and the battery so that the light bulb will not be turned "ON".