Abstract: The interface circuit described comprises a plurality of control stages, each of which can detect and indicate a short-circuit in the corresponding load or the associated power transistor.In particular, the interface circuit is arranged to disable a transistor permanently when short-circuits occur repeatedly in the load in order to prevent damage to the transistor.

Abstract: The system comprises: at least one spark plug, at least one ignition coil whose secondary winding is connected to the plug, a power transistor whose output path is in series with the primary winding of the coil between the two terminals of a direct-current voltage supply, and a control circuit for switching the transistor from the cut-off condition to the saturated condition to enable current to flow in the primary winding of the coil in order to generate a spark. Conveniently, the control circuit is arranged to switch the transistor progressively from the cut-off condition to the saturated condition, in dependence on the voltage detected between the terminals of its output path by the application of a driver signal which is first continuous and then pulsed.