A new valley-detection method for the quasi-resonance switching

To reduce switching losses in flyback topologies with a single switch, many kinds of quasi-resonant techniques are used. One of them is a valley-switching method which finds valleys of the drain-to-source voltage of the switch and makes the next switching begin at one of the valleys. It results in high efficiency and low EMI but an additional pin is required to detect where valleys are in view point of a control IC. This paper suggests a new valley-detection method without increasing the number of pin. Operational principles and experimental results will be shown to verify the validity of the proposed method.