High‐power‐factor dimmable LED driver with low‐frequency pulse‐width modulation

A novel dimmable light‐emitting diode (LED) driver is proposed in this study. The circuit topology uses two active switches. One active switch shared by a buck–boost converter and a buck converter is operated at high‐switching frequency while the other one is low‐frequency pulse‐width modulated to dim high‐power LEDs. The buck–boost converter plays the role of a power‐factor corrector. It operates at discontinuous‐conduction mode to waveshape the line current to be sinusoidal and in phase with the input‐line voltage. The buck converter regulates the dc‐link voltage to output a low‐frequency pulse‐width modulation (PWM) voltage to drive high‐brightness LEDs. Since only one power‐conversion process is required, and the buck converter works only when the low‐frequency PWM voltage is at a high level, the proposed LED driver has the advantage of high efficiency. Besides, it achieves unity power factor and low total current harmonic distortion.