Primary Side Sensing (PSS) is an emerging approach designed to cut components, save cost and improve isolation and safety within flyback SMPS designs.

Several companies have developed PSS controllers to monitor waveform changes in the auxiliary winding to the control IC – located on the primary, high voltage side - and then use those measurements to regulate the voltage and current outputs. This approach certainly removes the need for expensive optocouplers and all secondary-side feedback components but it also typically delivers supplies with poor voltage regulation and virtually no current regulation.