Abstract: A driver circuit for an electrical load device such as an indicator lamp includes the capability to both drive the lamp and to respond to a fault condition in the lamp to disable its energization. The circuit is adapted for control by a single I/O terminal of a programmable logic device. The I/O terminal being of the type having an internal architecture that causes the terminal to be pulled up to a logic high state when unloaded, and pulled down to a logic low state by either external loading or the closure of an internal; program-controlled switch forming part of a low-impedence path to ground. A processor-implemented test routine can be used to monitor the I/O terminal voltage and close the internal switch when the driver circuit responds to a shorted condition.

Abstract: An electronic control unit for regulating the air/fuel ratio of an internal combustion engine is disclosed. The electronic control unit includes an injector driver circuit which regulates the timing of the opening and closing operations of a plurality of electromagnetic solenoid injectors which input fuel to the engine. The injector driver circuit controls the injection with a pulse width modulated signal to supply an amount of fuel calculated from the operating parameters of the engine. The injector driver circuit is further provided with an energy dissipation circuit to assist in the rapid de-energization of the solenoid injectors. The energy dissipation circuit drains the energy stored in the rapidly collapsing magnetic field of a de-energized injector through a power device whose energy dissipation is controlled by the breakdown voltage of a Zener diode connected to the control terminal of the power device.