Analysis and design of a single-switch HPF AC/DC converter for driving power LEDs

This paper proposes a novel single-switch high-power-factor LED driver that is obtained by integrating a buck-boost converter and a flyback converter. Both converters share the same active switch. It results in reduction of power-conversion processes, leading to improving the circuit efficiency. The buck-boost converter performs the function of power-factor correction (PFC). The buck-boost converter can wave shape the waveform of the line current to be as the same as that of the input-line voltage when it operates at discontinuous-conduction mode. A nearly unity power factor and low total current harmonic distortion can be achieved. The flyback converter plays the role of the dc/dc converter that provides an isolated output voltage with very low voltage ripple to drive high-brightness light-emitting diodes. Since only one active switch is required, the proposed circuit is with simple control. Besides, it can meet the design goals of high power factor and low product cost.