Over-dwell protection circuit for an automotive ignition control system

摘要

An ignition control circuit ( 12 ) is responsive to a control signal (ESTC) to apply a drive signal (GD) to a power switching device ( 22 ) to conduct ignition coil current (I_C) therethrough. A resistor (R_S) included within the circuit ( 12 ) receives, and dissipates heat generated by, the coil current (I_C). The circuit ( 12 ) includes a first transistor (Q_HOT) positioned adjacent to the resistor (R_S) such that an operating temperature thereof is near that of the resistor (R_S), and a second transistor (Q_REF) positioned remote from the resistor (R_S) and having an operating temperature defining a reference temperature. The first and second transistors (Q_HOT, Q_REF) are configured to produce an output voltage (V_OUT) proportional to a difference in operating temperatures thereof, and a latch circuit (L 1 ) disables the control signal (ESTC) to thereby turn off the power switching device ( 22 ) when the output voltage (V_OUT) difference exceeds a reference voltage (V_REF).