The ignition coil is divided into two types: open magnetic type and closed magnetic type according to the magnetic circuit. The traditional ignition coil is of the open magnetic type, and its core is stacked with silicon steel sheets of about 0.3 mm, and the core is wound with secondary and primary coils. In the closed magnetic type, an iron core similar to III. is used to wind the primary coil, and the outer coil is wound around the secondary coil, and the magnetic field lines are formed by the iron core to form a closed magnetic circuit. The advantages of closed magnetic ignition coil are less magnetic flux leakage, small energy loss and small volume, so the electronic ignition system generally adopts closed magnetic ignition coil.