Fuel injector driver circuit

Abstract

A circuit is described for energizing an electromagnetically operated fuel injector from an unregulated voltage source in response to an injection command pulse. The injector pull-in current is provided by directly coupling the unregulated voltage across the injector upon the initiation of the injection command pulse. The injector current is thereafter reduced to a lower hold-in value. The circuit is voltage compensated by a pair of timers the first of which compensates for the voltage dependent injector pull-in time by adjusting the time that the unregulated voltage is directly applied across the injector as a function of the value of the unregulated voltage to insure that the injector is energized for all values of the unregulated voltage while minimizing the time period that the unregulated voltage is directly coupled across the fuel injector. The second timer extends the time of injector energization beyond termination of the injection command pulse by a time period dependent upon the value of the unregulated voltage so as to compensate for the voltage dependent injector pull-in time so that the injector is energized for a time period substantially equal to the injection command pulse for all values of the unregulated supply voltage.