With the development of automobile gasoline engine in the direction of high speed, high compression ratio, high power, low fuel consumption and low emissions, the traditional ignition device is no longer suitable for use. The core components of the ignition device are the ignition coil and the switch device. When the energy of the ignition coil is increased, the spark plug can produce enough energy spark, which is the basic condition for the ignition device to adapt to the operation of modern engines.
Generally, there are two groups of coils in the ignition coil, the primary coil and the secondary coil. The primary coil is wrapped with thick enameled wire, usually about 0.5-1 mm enameled wire for about 200-500 turns; The secondary coil is made of thinner enameled wire, usually about 0.1mm enameled wire is used for about 15000-25000 turns. One end of the primary coil is connected with the low-voltage power supply (+) on the vehicle, and the other end is connected with the switching device (breaker). One end of the secondary coil is connected with the primary coil, and the other end is connected with the output end of the high-voltage line to output high-voltage electricity.

The reason why the ignition coil can turn the low voltage power on the vehicle into high voltage is that it has the same form as the ordinary transformer, and the turn ratio of the primary coil is larger than that of the secondary coil. However, the working mode of the ignition coil is different from that of the ordinary transformer. The working frequency of the ordinary transformer is fixed 50Hz, also known as the power frequency transformer. The ignition coil works in the form of pulse, which can be regarded as a pulse transformer. It repeatedly stores and releases energy at different frequencies according to different engine speeds.

When the primary coil is connected to the power supply, a strong magnetic field is generated around with the increase of the current, and the iron core stores the magnetic energy; When the switch device disconnects the primary coil circuit, the magnetic field of the primary coil decays rapidly, and the secondary coil will induce a high voltage. The faster the magnetic field of the primary coil disappears, the greater the current at the moment of current disconnection, and the greater the turn ratio of the two coils, the higher the voltage induced by the secondary coil.