Research On A Single-stage Isolated Electrolytic Capacitor-less LED Driver

Light Emitting Diodes(LED)are regarded as a new generation of green light sources due to their long life and high efficiency,and they have been widely used now.Driver is the key component of LED lighting source.In order to reduce the harmonic pollution,the input current and the input sinusoidal voltage are required to be in the same frequency and phase when the traditional AC power grid supplies power to the driver.Electrolytic capacitors are often used in traditional driver to ensure power balance.The life of electrolytic capacitors is much shorter than that of LED,which seriously hinders the development of driver.Therefore,the research of electrolytic capacitor-less LED driver with high power factor has important engineering application value.Firstly,the principle of eliminating electrolytic capacitor is described in thesis.Based on the traditional single-stage LED driver topology without electrolytic capacitor,its working mode and circuit characteristics are analyzed.And then it is verified by simulation.Secondly,in consideration of the disadvantages of the traditional topology,a single-stage isolated LED driver without electrolytic capacitor is proposed.The electrolytic capacitor is replaced by the capacitor with small capacitance by increasing the voltage ripple of the energy storage capacitor.The working mode and electrical characteristics of the topology are analyzed in detail,and the simulation results are compared and analyzed.Compared with the traditional Flyback transformer,the transformer in the form of bidirectional excitation to achieve electrical isolation is designed in the proposed topology.This not only makes up for the poor anti-interference ability and low safety performance of non-isolated topology,but also improves the utilization rate of the magnetic core and the power density of the driver.The primary side of the transformer adopts a Boost converter to realize the power factor correction function,and the secondary side introduces an inductor to further reduce the output current ripple.Thirdly,the proposed topology is modeled based on the state space averaging method.Combined with the transfer function of the control loop,the transfer function between the main variables is derived.The output results of circuit model and mathematical model are compared to analyze the system performance.Finally,the overall structure of the prototype is designed.The parameters of the prototype are calculated in detail,and the selection basis of the device and the design of the control circuit are given.An experimental prototype with a power of 60 W is built for verification.The experimental results prove that the single-stage isolated electrolytic capacitor-less LED driver achieves bidirectional field excitation,the power factor value reaches 98%,and the output current ripple is reduced to 2%,which has certain feasibility and superiority.