Circuit configuration for a self-oscillating blocking oscillator switched-mode power supply

A circuit configuration for a self-oscillating blocking oscillator switched-mode power supply for drawing sinusoidal current from a power source, comprising a transformer having a primary winding, a bridge rectifier having an output terminal for providing a positive voltage, a semiconductor switch element for clocked application of an alternating voltage rectified by said bridge rectifier and unsmoothed to said primary winding, a control device having input terminals, an RC element providing a primary current signal, a voltage divider coupled in parallel to said RC element and providing a undervoltage detection signal for said alternating voltage, and a one-way rectifier configuration having an input side and an output side, said primary current signal being applied to one of said input terminals of said control device, said undervoltage detection signal being applied to another one of said input terminals of said control device, said control device triggering in pulse-width modulation mode said semiconductor switch element according to the primary current signal, said input side of said one-way rectifier being connected to said output terminal of said bridge rectifier, said RC element and said voltage divider being connected to said output side of said one-way rectifier.