A Single-stage High Frequency LED Driver Based On Class-E Converter With Digital Control

The conventional LED driver is a two-stage system, which is constructed by a constant current control DC/DC converter with a power factor correction(PFC) stage. Though easy to design, the two-stage solution is still less comparative due to the high cost of more than one independently control circuits and power switches. Therefore, the single-stage LED driver has been studied for many years. In this paper, a single-stage based on Class-E resonant converter was presented. Class-E converter is a widely used single-switch topology, and the conversion in the switch and diodes can be accomplished at ZVS and ZCS mode, respectively. Therefore, the converter proposed was designed to work at 500 k Hz.According to the graft scheme, a series of topologies based on the Class-E converter was proposed. To meet the IEC 61000-3-2 Class C standard, an active PFC, along with an EMI filter, is indispensable. However, the different topologies will affect the shared switch present overvoltage or overcurrent feature. Take the system cost, the buck-boost circuit was finally chosen.The operational principle of the whole system and the two-separated part was analyzed in detail. In the meantime, fundamental analysis was adopted to design the component parameters, making the switch work in the optimal state. In addition, impedance matching network was used to realize the soft-switching characteristics in the full load range. The component parameters had an influence on the bus voltage and the working state of the front-end when the input voltage or the output power change, and this effect was illustrated in diagram in this paper.In order to design the control circuit, extended describing function method was moved from the series resonant converter to the Class-E converter to derive the small signal model. Based on the fact that the resonant capacitor behaved like an equivalent inductor with respect to the modulation frequency, the equivalent circuit model was derived, which could predict the dynamic behaviors very well. Besi des, digital compensation circuit and high frequency control method was designed.A 100 W laboratory prototype was built to verify the theoretical analysis. The system PF is higher than 0.99, THD is less than 5.7%, and the efficiency is as high as 90.5% in the full load state.