Quasi-resonant Flyback LED Driver Power Supply Research And Design

Semiconductor LED (lighting-emitting diode), which has long lifetime, energy-saving, higher luminous efficiency characteristics, has been widely used in industrial equipments, automotive electronics, general lighting and portable equipments. For general lighting purposes, a48W phase-controlled dimmable LED driver power supply is designed, combined with TRIAC dimmer. The main contents are as follows:(1) The characteristics of LED solid light source, topologies of power supply and common dimming methods are analyzed. A solution of LED driver based on quasi-resonant flyback is proposed, which uses TRIAC dimmer to achieve dimming function; Power Factor Correction (PFC) technology is analyzed as well and the LED power supply is finalized with the implement of a single-stage PFC design; Flicker problem in LED driver caused by the phase-controlled dimmer, especially in TRIAC, is analysed and the corresponding solutions are also given.(2) The question of how the quasi-resonant (QR) flyback converters to achieve zero-voltage (ZVS) and switching frequency characteristics in the process are also analysed; The converter input current tracking input voltage to achieve high PF value in current critical mode (BCM) is theoretically derived, and parameters calculations are given, which enables easily the subsequent design of transformer.(3) The high-frequency transformer is designed in detail based on the above analysis; According to the design parameters, LED driver power supply is designed based on controller SSL2129and the main circuit, control circuit, dimming circuit, EMI filter circuit have been analysed and designed; Dynamic Ton control technology is used to control the ramp current of converter’s pin TONMOD, which enables the design of a mains dimmable driver.(4) The phased dimming LED driver power supply is experimented. Experiments show that the power supply is working properly and meets the requirements of the system; Supply output current is maintained at around1A and the power factor is always above0.9within200～253VAC input voltage range; The system has no noise, no flicker during the dimming process, verifying the theoretical analysis.