The Analysis And Research Of Efficiency Of Single-stage PFC Flyback LED Drive

Single-stage PFC flyback LED driver has been widely used in the field of small and medium power LED driver due to simple structure and low price. However, because this structure uses usually a fixed conduction time to achieve PFC function, the change of frequency is larger, especially when the loads is light, frequency will be very high and efficient will be low. Meanwhile, the leakage inductance of primary and secondary windings of the transformer in flyback topology are larger,so that loss is serious.Therefore, studying flyback LED driver’s efficiency is particularly important.The thesis designed a single-stage PFC flyback LED driver chip based on a quasi-resonant technology. Meanwhile, designed a boundary control LED driver structure in order to compare. Chip peripheral used primary side feedback methods, internal circuit include valley detection module, the secondary inductance zero crossing detection module, the output current pre-processing module, an error amplifier module, the drive output modules,undervoltage overvoltage protection modules and so on. Dued to achieve constant current, PFC and quasi-resonant function simultaneously, the circuit needed a compromise deal.The paper analyzed the main loss sources of switching power, and some common techniques to improve efficiency, compared the advantages and disadvantages of single-stage PFC and two-stage PFC. According to the design objectives and requirements, completed the design of whole circuit and analyzed the efficiency in principle, designed and simulationed a part of the sub-modules circuits. When the input voltage range is 85²65VAC, output power is 12 W, the average efficiency of the quasi-resonant mode of LED driver is 93.04%, PF is 0.92, the average efficiency of the boundary mode of LED driver is 87.95% in TSMC₀.5μm BCD process. It shows that quasi-resonant technology can effectively improve the single-stage PFC flyback LED driver’s efficiency. LED driver’s average efficiency is 92.5% in the full voltage and the whole load range, which proves that the quasi-resonant technique have practicality in single-stage PFC LED driver circuit.