A Novel Control Scheme of Quasi-Resonant Valley-Switching for High-Power-Factor AC-to-DC LED Drivers

This paper presents a novel control scheme of quasi-resonant (QR) mode and valley-switching for high-power-factor (PF) ac-to-dc light-emitting diode (LED) drivers. The proposed driver control scheme is based on a buck PF corrector converter, which is operated in QR valley-switching. The proposed control scheme can directly sense the QR valley signal from the current sensor, and it is definitely different from the conventional method which senses the QR valley signal from auxiliary winding. The cost and size of the driver circuit can be remarkably reduced when the proposed control scheme is adopted. Furthermore, the proposed circuit can provide not only high PF and low total harmonic distortion but also high conversion efficiency. Up to 0.99 PF and 91.5% efficiency are obtained from an 8-W (40-W replaced) LED bulb driver prototype.