High Power Factor Single Stage Flyback Converter for Dimmable LED Driver

Single stage Flyback converter with active power factor correction (PFC) function built-in is very popular for low power LED driver application. However, a universal driver design (120V similar to 277Vac wide input) for meeting PF>0.90 and THD<20% at 50% of maximum output power remains very challenging using peak current transition mode (PCTM) PFC control. Therefore, in this paper, a novel and practical scheme is presented for a single stage Flyback LED driver to achieve high power factor for universal input. Based on LED output feedback, the off-time is controlled to operate the Flyback converter in discontinuous conduction mode (DCM) to realize high PF. The control implementation can be adapted to existing popular PCTM PFC controller and due to the secondary side current regulation, it is suitable for dimmable LED driver application. A 22W dimmable LED driver is prototyped to verify this scheme and at 10W output power, PF>0.90 and THD<20% are achieved for the universal input voltage range.