Ignition Coil & Power Transistor: Operation

• When the power transistor unit is switched on by the signals from the engine control unit, the primary current of the ignition coil will flow. When the power transistor unit is switched off, the primary current flow is interrupted, and high voltage is produced at the secondary coil. See Fig 1 .
• When the engine control unit switches off the power transistor within the unit, the battery voltage within the unit is applied to the power transistor unit, and the power transistor unit is switched on. In addition, the power transistor unit is switched off when the engine control unit switches on the power transistor within the unit.

Fig 1: Identifying Ignition Coil & Power Transistor Circuit

Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.