Method for operating an ignition device for an internal combustion engine, and ignition device for an internal combustion engine for carrying out the method

A method for operating an ignition device for an internal combustion engine, which ignition device comprises an ignition coil embodied as a transformer, a spark plug connected to a secondary winding of the ignition coil, a drivable switching element connected in series with a primary winding of the ignition coil, and a control unit connected to the primary winding of the ignition coil and a control input of the switching element, wherein the control unit is configured to provide an adjustable supply voltage for the ignition coil and a drive signal for the switching element depending on currents through the primary and secondary windings of the ignition coil and a voltage between a connecting point of the primary winding of the ignition coil to the switching elemeht and a negative terminal of the supply voltage, the method comprising:

• in a first phase, the switching element is switched by the drive signal to be conducting at a first switch-on instant and to be non-conducting again at the predefined ignition instant,
• in a subsequent second phase, the primary voltage or a voltage derived therefrom is compared with a first threshold value and, in the case of said voltage falling below the first threshold value, the switching element is switched to be conducting again at a second switch-on instant,
• in a subsequent third phase, the supply voltage is regulated such that the current through the secondary winding of the ignition coil approximately corresponds to a predefined current and the current through the primary winding of the ignition coil is compared with a predefined second threshold value and, in the case of said current exceeding the second threshold value, the switching element is switched to be non-conducting again at a first switch-off instant,
• in a subsequent fourth phase, the current through the secondary winding of the ignition coil is compared with a third threshold value and, in the case of said current falling below the third threshold value, the switching element is switched to be conducting again at a third switch-on instant,
• subsequently the third and fourth phases are repeated until a predefined burning duration is reached at an instant, at which point the switching element is finally switched to be non-conducting.