Switched-mode power supply designed to supply power to a consumer (S), with an output voltage (U out ) regulated to a target value (U s ), with - a supply path, which comprises a switching regulator controlled by a driver , a galvanically isolated transformer which is situated downstream from the switching regulator , and an output circuit comprising a rectifier which is situated downstream from the transformer , wherein the consumer (S) can be connected to the output of said output circuit, and - a feedback path via which a signal is supplied to the driver , said signal representing the output voltage (U out ) and being transmitted via a light source and a light receiver , wherein, on the basis of said signal, the driver regulates the output voltage (U out ) to the target value (U s ) via a corresponding control of the switching regulator , - wherein the feedback path comprises a current regulator , which regulates a current flowing via the light source to a current value corresponding to the output voltage (U out ), and - wherein the light source is used in the feedback path without a series resistor (Rv) upstream from the light source , characterized in that - the feedback path comprises a voltage regulator , which comprises a downward voltage switching regulator, particularly a synchronous downward voltage switching regulator, and regulates a feed voltage dropping over the light source at an output voltage (U out ) in the range of 4.5 V to 45 V to a fixed value, in the range of 3 V to 5 V, below the target value (U s ), - wherein the light source comprises a light element, specifically a light emitting diode, particularly an infrared light emitting diode, whose brightness changes depending on a current flowing through it, and - wherein an isolator , specifically a printed circuit board, is arranged between the light source and the light receiver , said isolator being transparent in the range of the wavelength of the light emitted by the light source . - a supply path, which comprises a switching regulator controlled by a driver , a galvanically isolated transformer which is situated downstream from the switching regulator , and an output circuit comprising a rectifier which is situated downstream from the transformer , wherein the consumer (S) can be connected to the output of said output circuit, and - a feedback path via which a signal is supplied to the driver , said signal representing the output voltage (U out ) and being transmitted via a light source and a light receiver , wherein, on the basis of said signal, the driver regulates the output voltage (U out ) to the target value (U s ) via a corresponding control of the switching regulator , - wherein the feedback path comprises a current regulator , which regulates a current flowing via the light source to a current value corresponding to the output voltage (U out ), and - wherein the light source is used in the feedback path without a series resistor (Rv) upstream from the light source , characterized in that - the feedback path comprises a voltage regulator , which comprises a downward voltage switching regulator, particularly a synchronous downward voltage switching regulator, and regulates a feed voltage dropping over the light source at an output voltage (U out ) in the range of 4.5 V to 45 V to a fixed value, in the range of 3 V to 5 V, below the target value (U s ), - wherein the light source comprises a light element, specifically a light emitting diode, particularly an infrared light emitting diode, whose brightness changes depending on a current flowing through it, and - wherein an isolator , specifically a printed circuit board, is arranged between the light source and the light receiver , said isolator being transparent in the range of the wavelength of the light emitted by the light source . <EOS>