Resonant LED driver with inherent constant current and power factor correction

A drive converter for light emitting diodes is presented, which is able to add the constant current operation mode and power factor correction without any control feedback or special control algorithm while obtaining very good performances regarding high efficiency, good reliability and most importantly, low cost. The converter is based on a half bridge resonant topology, controlled with a discrete self-oscillating drive circuit, with an output parallel resonant tank. The working principle is based on the inherent current source behaviour of these kinds of converters, allowing a high power factor and low harmonic distortions. One topology uses no electrolytic high or low voltage filtering capacitors, thus obtaining a longer working lifetime for the driver. In addition, a second topology with output non-electrolytic condenser filtering for higher performances in dimming applications is proposed.