Abstract: An improved dual limit solenoid driver control circuit is disclosed in which solenoid current is sensed and provided as an input to two separate comparators (24, 25). Each comparator receives, during a solenoid pull-in (initial) period (T.sub.1), fixed maximum and minimum reference threshold levels which determine the maximum and minimum current limits (I.sub.max, I.sub.min) for solenoid current during initial pull-in excitation. Subsequently during a hold period T.sub.2 following the pull-in period, each of the comparators receives different maximum and minimum thresholds so as to establish holding solenoid current limits (H.sub.max, H.sub.min). The outputs of the compartors are connected as inputs to a set/reset flip flop (32) whose output controls the operation of a solenoid driver circuit (15). A monostable multivibrator (33) reacts to an initial control pulse (41) to produce a predetermined pull-in time pulse (43) that results in the maximum and minimum pull-in solenoid current limits.

Abstract: In a solenoid fuel injection system, an output transistor (16) receives switching signals to control through current therein which is provided to a solenoid fuel injection coil (11) in series with a current sensing resistor (17). A current control circuit (12) provides pulse width modulation control of solenoid current by monitoring the voltage across the sensing resistor. The fault detection circuit provides separate fault signals for short circuits at either the first or second end terminals (E, H) of the solenoid coil. Separate voltage comparators (18, 23) monitor voltages at the first and second end terminals, and separate delay timers (20, 25) effectively gate the comparator outputs to indicate actual detected short circuits. Each of the fault detection signals sets a fault latch (22) which then acts to reduce current through the output transistor and coil. The fault latch is periodically reset.