Electrolytic capacitor-less AC-DC LED driver with constant output current and PFC

Recent developments in improving lighting efficiency and cost reduction of LED's have caused them to be a suitable alternative for the current lighting systems. In this paper a novel off-line structure is proposed to drive LED's. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn't use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) Flyback converter in order to have power factor correction (PFC). A Buck converter is added to the third winding of the Flyback transformer in order to create two paths for the electrical power. DC power will get to the load through one stage converter (Flyback) and AC power will get to the load through two stage converter (Flyback+Buck). Therefore, the efficiency is improved in comparison with a regular two-stage circuit, as well as, having a low output current ripple. Principles of operation are presented as well as closed-loop simulation results for a 700mA / 20W prototype.