Switching control system to reduce coil output voltage when commencing coil charging

Abstract

A switching control system and method is provided that optimizes switching efficiencies for power switching applications including automotive ignition systems, solenoid drivers, motor drivers and power regulation systems. In an ignition system, a coil current switching magnitude is controlled at the start of ignition coil charging, thereby avoiding an untimely spark event. When the transistor threshold voltage is reached, the collapse rate of the ignition system transistor collector voltage is reduced by reducing the gate charging current. The reduced collector voltage slew rate results in a reduced primary and secondary coil output voltage. After the collector voltage collapses, a continued rapid charge is provided to place the transistor in a hard saturation bias condition. In an aspect, the present invention dynamically determines the threshold voltage of a power transistor. A mirror capacitor substantially matches a transistor gate voltage and a signal is generated when the mirror capacitor voltage proportionally exceeds the transistor gate voltage as a consequence of the transistor reaching a threshold voltage.