Abstract: A lower-cost and more precise control methodology of regulating the output current of a Flyback converter from the primary side is provided, which works accurately in both continuous current mode (CCM) and discontinuous mode (DCM), and can be applied to most small, medium and high power applications such cell phone chargers, power management in desktop computers and networking equipment, and, generally, to a wide spectrum of power management applications. Two highly integrated semiconductor chips based on this control methodology are also described that require very few components to build a constant current Flyback converter.