Thermal clamp for an ignition coil driver

摘要

A circuit in an ignition system having a switchable current drive circuit responsive to a first control signal, and a charging circuit responsive to the switchable current drive circuit for providing a current through a coil to charge the coil when the switchable current drive circuit is enabled by the first control signal being in a first logic state and for collapsing the current through the coil thereby producing a rising voltage across the coil to fire a spark plug, typically coupled across the coil, when the switchable current drive circuit is disabled by the first control signal being in a second logic state. The circuit includes a thermal clamping circuit responsive to a second control signal and coupled to the charging circuit for providing current to the charging circuit to slowly discharge the coil and for clamping the voltage at the coil to a predetermined voltage such that the firing of the spark plug is prevented. The thermal clamping circuit is activated when the temperature of the ignition system exceeds a predetermined temperature.