1. Introduction The AP3768 is the generation II Primary Side Regulation (PSR) controller, which uses Pulse Frequency Modulation (PFM) method to realize Discontinuous Conduction Mode (DCM) operation for flyback power supplies. The AP3768 can provide accurate constant voltage, constant current (CV/CC) regulation. In order to achieve the excellent voltage regulation, AP3768 has a programmable cable voltage drop compensation function to accommodate various cables with different gauges and lengths.