The NCP1343 is a highly integrated quasi−resonant flyback controller suitable for designing high−performance off−line power converters. It features a proprietary valley−lockout circuitry, ensuring stable valley switching. This system works down to the 6th valley and transitions to frequency foldback mode to reduce switching losses. As the load decreases further, the NCP1343 enters quiet−skip mode to manage the power delivery while minimizing acoustic noise. Additionally, the NCP1343 integrates power excursion mode (PEM) to minimize transformer size in designs requiring high transient load capability.