Abstract: A single pulse blocking converter for generating of a constant output voltage has a switching transistor and a transformer wherein a feedback effect of the transformer supplies the base current of the switching transistor by way of the collector-emitter path of a driving transistor. The driving transistor is controlled by means of a control transistor in dependence upon a measured voltage which is in proportion to the output voltage of the blocking converter. The circuit is particularly characterized in that an auxiliary circuit is provided with a transistor which, during the transition of the switching transistor from the conductive into the blocked condition, applies a blocking voltage to the control path of the switching transistor and in that, by means of a periodic resetting of the auxiliary circuit by the pulses from a pulse generator, the blocking voltage is switched off and a new switching period is initiated for the switching transistor.