Abstract: In order to obtain a stable dc output from a switching regulator of a type in which a switching control arrangement is provided with an optical coupler, an A-D converter is arranged to provide the optical coupler with a digital error signal. This error signal corresponds to a difference between the regulated dc output and a reference voltage. The digital output of the optical coupler is converted into a corresponding analog signal at a D-A converter. The output of the D-A converter is applied to a comparator and is compared thereat with a reference signal voltage for controlling a switching device.