Compensated dual injector driver

Abstract

A compensated dual injector driver circuit for controlling the current to either of a pair of electromagnetic solenoid fuel injectors is disclosed. The driver circuit includes a pair of analog bilateral switches operably connected to the control terminals of two driver transistors whose power terminals are coupled serially with the coils of the injector solenoids. A driver amplifier generating a current control signal for the driver transistors is connected to a common input of the two switches. Either of the switches is selected for closure by a logical input from a select line thereby choosing the individual injector to be energized. The driver amplifier in response to the leading edge of a control pulse regulates the conductance of the selected transistor with the current control signal to initially draw current through the injector coil until it reaches a peak value. At the time the peak current is attained, the driver amplifier then switches the control current to a holding value. The peak and the holding current levels are measured by a negative feedback loop from a sense resistor commonly connected in series with each set of coils and driver transistors to indicate the magnitude of current therethrough. The circuit further includes a means for controllably collapsing the magnetic field stored in the injector coils when the injector driver transistors are turned off in response to the trailing edge of the control pulse. Compensation is provided to the driver amplifier for altering the hold level current in accordance with variations in the battery voltage. The differing levels of hold current with changing battery voltage will modify the closing time of the injector oppositely to those changes produced in the opening times by the battery voltage.