Electronic Spark Control Module: Description and Operation

Ignition Coil With Power Output Stage:

Power Output Stage, Ignition Coil, And Connector:

Audi vehicles use one of two different styles of power output stages (depending on which style of ignition coil is used). Although they are different in appearance, they operate in the same way. The ignition power output stage consists of a power transistor and integrated circuit. It is used to make and break the primary circuit, and to regulate the current through the ignition coil. It receives a triggering signal from the ECU. The ECU applies power to the output stage, which turns it ON. In this ON state, current flows through the primary circuit of the ignition coil. When the ECU determines it's time for a spark, the power to the output stage is momentarily interrupted. The transistor turns OFF, breaking the primary circuit, and inducing a high voltage spark in the secondary circuit. The ECU regulates the duration of the interruption in the trigger signal, and thus regulates the dwell angle, and charging time. The longer the interruption, the smaller the dwell angle and the shorter the charge time. This is comparable to the point gap in a standard point type ignition system, where the larger the point gap, the smaller the dwell angle, and the longer the interruption in the primary current. Because the switching is electronic, the dwell can be increased to very large angles and still ensure a complete break in the primary current when a spark is needed.