Automotive ignition system lockup protection circuit

摘要

An automotive ignition system lockup protection circuit utilizes a capacitor charging/discharging circuit to generate a periodic clock signal. A counter circuit activates an ignition coil deenergizing signal after a predetermined number of clock signal. The capacitor charges and discharges within a voltage reference window defined as the difference between a first reference voltage and a second larger reference voltage, wherein the first reference voltage is functionally related to a variable battery voltage and the second reference voltage is fixed and independent of battery voltage. The frequency of the periodic clock signal is modulated in accordance with the voltage reference window to thereby vary the lockup time in accordance with battery voltage. The capacitor charging and discharging current is adjustable to compensate for variations in the capacitor value and the entire circuit operates consistently over a temperature range typically required in an automotive application.