Releasing circuit for actuating vehicular safety device

Abstract

A circuit for controlling the actuation of a vehicle air bag system includes a two terminal electrically actuated ignition element connectable to a drive voltage line through a first transistor and to a circuit ground through another transistor. The voltage source includes the vehicle battery and a capacitor that is charged by the vehicle battery and which supplies operating power in the event the vehicle battery is removed from the circuit, for example, as a consequence of a collision. The transistors are normally biased to a non-conducting state sufficient to isolate the ignition element from the drive voltage source and circuit ground. Vehicle acceleration is sensed by an acceleration sensor which, in the event of a collision, biases both transistors into conduction to effectively connect the two terminals of the ignition element to the drive voltage line and to ground to actuate the vehicle air bag. During normal operation, a bias circuit controls one of the transistors to provide a minute current flow that is used to sense fault conditions and illuminate an alarm lamp. During a collision, the acceleration sensing circuit re-configures the bias circuit to drive both transistors into conduction. A low-voltage circuit senses the drive voltage and controls the bias to the one transistor to inhibit the minute current flow to conserve power during low-voltage conditions.