Digital primary-side sensing control for flyback converters

Primary-side sensing (PSS) technique can be used for the output voltage or current regulation by employing an auxiliary winding. However, the sensed voltage may be corrupted by switching noise due to leakage inductance, winding resistance, and nonlinearity of the magnetic core, therefore the sensed voltage can only achieve limited accuracy. With the advance of power control IC realization technology, more complicated control and estimation algorithms can be realized by using analog, digital, or mixed-signal technologies. This paper introduces a digital control method to make the influence of nonideal factors as low as possible. A key factor for accurate voltage sensing is the determination of sampling instant on the auxiliary winding. A prototype of a DCM DC/DC flyback converter with digital signal processor has been realized to verify the proposed digital PSS scheme.