Electronic fuel injector driver circuit

An electronic driver circuit for controlling the energization of a solenoid coil, forming part of an electromagnetic fuel injection valve, in response to an injector control pulse, produced by a main fuel injection control circuit, comprising:

• a current regulating circuit including a power transistor connected in series with said coil, forming part of an electromagnetic fuel injection valve, and a current sensing resistor between a power source and ground, and a first switching transistor responsive to said injector control pulse, produced by a main fuel injection control circuit, for controlling the actuation of said power transistor;
• a free-wheeling circuit connected in parallel with said power transistor and including a diode and a second switching transistor actuation of which is also controlled by said first switching transistor so that said free-wheeling circuit is operative to allow current to flow to said solenoid coil, forming part of an electromagnetic fuel injection valve, during said injector control pulse, produced by a main fuel injection control circuit;
• a first comparator having one input thereof connected to said current sensing resistor and its other input thereof connected to receive a first reference signal from a reference circuit, said first reference signal being set so that said first comparator switches output states when the current through said coil attains a predetermined peak current value;
• the output of said first comparator being connected to said reference circuit for changing the value of said first reference signal when said first comparator switches output states so that said first comparator will not switch back to its original output state until the current through said coil, forming part of an electromagnetic fuel injection valve, is substantially equal to zero;
• and
• a second comparator having its output connected to a third switching transistor which is in turn connected to said power transistor for controlling the actuation of said power transistor, said second comparator having one input thereof connected to said current sensing resistor and its other input connected to receive a second reference signal from said reference circuit;
• said second reference signal being set so that initially said second comparator switches output states in response to said first comparator switching output states to thereby actuate said third switching transistor and deactuate said power transistor;
• said second reference signal being thereafter changed by the effect of the switched output state of said first comparator on said reference circuit to a voltage value substantially equal to the voltage across said current sensing resistor when the current through said coil, forming part of an electromagnetic fuel injection valve, is equal to a predetermined hold current level;
• said second comparator further having positive feedback for providing a hysteresis effect to said second comparator for oscillating the output of said second comparator to cycle said power transistor on and off to substantially maintain the current through said coil, forming part of an electromagnetic fuel injection valve, at said predetermined hold current level;
• said free-wheeling circuit remaining actuated during the off periods of said power transistor so that the current through said coil, forming part of an electromagnetic fuel injection valve, decays slowly when said power transistor is off.