Abstract: A DC-to-AC voltage converter having galvanically separate onput and output circuits, and comprising a converter transformer having at least one primary winding; a resonance capacitor connected to said at least one primary winding; a switching transistor, of which the collector-emitter path is series-connected to the at least one primary winding; and drive means for the switching transistor, wherein charge storage in the base-collector area of the switching transistor provides base drive for the switching transistor, and further comprising control means for detecting an increase of the collector-emitter voltage (Uce) of the switching transistor and for providing in response to such an increase and at least in a period of time directly following the increase, an additional base drive current for the switching transistor, which additional base drive current is gradually increased at a predetermined rate in such a manner that the storage time of the switching transistor remains substantially constant over the ope