An ignition system for an IC engine has at least one ignition coil and in series with the primary is a switch triggered by a control unit (12). In each branch between the secondary and a spark plug is a high voltage sweep diode. In series with this but parallel to the plug itself is a switch (18) triggered by the same control unit. Between the high voltage end of the secondary and the plug is a circuit to limit the switch-on voltage. The control unit switches off the coil charging current directly before the end of a coil charging process and then back on again. The switch is triggered simultaneously so that a conditioning current flows in the sweep diode.
