Electronic fuel injector driver circuit

Abstract

A method of and apparatus for controlling the energization of an electromagnetic fuel injection valve in response to the production of an injector control pulse in an electronic fuel injection system. The driver circuit operates a current regulating power transistor into saturation until the current through the solenoid coil of the injector valve attains a predetermined peak current value. A comparator circuit deactivates the power transistor to stop the build-up of current through the coil. A switched free-wheeling circuit is enabled, remains activated, and starts conducting when the power transistor is deactivated by the comparator circuit so that some current continues to be supplied to the solenoid coil when the power transistor is off, thereby causing the current through the coil to decay slowly. When the solenoid current has decayed to a predetermined hold current level, the comparator circuit reactivates the power transistor and thereafter, due to hysteresis in the comparator circuit, cycles the power transistor on and off to substantially maintain the current through the coil at the predetermined hold current level. At the end of the injector control pulse, both the current regulating power transistor and the switched free-wheeling circuit are deactivated. Then, through multiple power dissipation pathways momentarily activated by the avalanching of a zener diode in series with the injector's solenoid coil, the energy stored in the solenoid coil and the current through the coil diminish rapidly to zero.