A two-stage quasi-resonant dual buck LED driver with digital control method

A two-stage quasi-resonant LED driver with digital control method is proposed in this paper. The first stage of this converter is a boost circuit with power factor correction (PFC) function and the second stage is a dual Buck circuit which works in quasi-resonant zero voltage switching (ZVS) state. Because of the soft switching characteristics of the converter, switching losses are reduced and efficiency is improved greatly. Digital control method is adopted to detect the peak value of inductor current and enhance the reliability of the system. Moreover, as LEDs are always driven by current source, a current loop is designed to maintain output current constant. IRS2104 is chosen as the drive chip and microcontroller is AT90PWM216 which can improve the quality of the drive signals. The output of the converter is a square wave which drives two branches of antiparallel LEDs. A 60W prototype has been designed to demonstrate theoretical analysis. Obtained power factor was as high as 0.987, and efficiency was up to 92.3%.