An LFPWM dimmed LED driver featuring high power factor

A novel dimmable LED driver is presented in this paper. The circuit topology uses two active switches. One active switch shared by a buck-boost converter and a buck converter is operated at a high-switching frequency while the other one is low-frequency pulse-width modulated to dim high power light-emitting diodes (LED). The buck-boost converter plays the role of a power-factor corrector (PFC). It operates at discontinuous-conduction mode (DCM) 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 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 a unity power factor and a low total current harmonic distortion (THDi).