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 .