Ignition systems have two circuits that result in a spark being fired at the end of a spark plug. The primary circuit is between the battery and the ignition coil. The secondary circuit is between the ignition coil and the spark plug.
Here’s an overview of how different systems operate.
An automotive ignition system is divided into two electrical circuits -- the primary and secondary circuits.
Like conventional ignition systems, electronic systems have two circuits: a primary circuit and a secondary circuit. The entire secondary circuit is the same as in a conventional ignition system. In addition, the section of the primary circuit from the battery to the battery terminal at the coil is the same as in a conventional ignition system.
With the ignition switch turned on, primary (battery) current flows from the battery through the ignition switch to the coil primary windings. The primary current is turned on and off by the action of the armature as it revolves past the pickup coil or sensor. Each tooth of the armature near the pickup coil creates a voltage that signals the electronic module to turn off the coil's primary current. A timing circuit in the module will turn the current on again after the coil field has collapsed. When the current is off, however, the magnetic field built up in the coil is allowed to collapse, which causes a high voltage in the secondary windings of the coil. It now operates on the secondary ignition circuit, as in a conventional ignition system.
The third type of ignition system is the distributorless ignition. The spark plugs are fired directly from the coils. An ignition module and the engine computer control spark plug timing. The distributorless ignition system may have one coil per cylinder or one coil for each pair of cylinders.
There are several advantages of not having a distributor: