High Frequency LED Driving Technology Based On Quasi-resonat Dual Buck Circuit

Traditional LED driver is a two-stage topology,which is composed of power factor correction stage and DC/DC stage.Two-stage converter has the advantages that each stage can be designed separately with easier design method,and the control of each stage is more accurate.In this paper,in order to increase the efficiency and power density further,a quasi-resonant dual Buck circuit which is suitable for higher frequency applications is proposed.The switches work in soft switching state and the system obtains high efficiency and power density.The major research contents are introduced as follow.In this paper,dual Buck circuit is analyzed in detail and the condition constraint of quasi-resonant state is obtained,and an optimized parameter design method is also proposed.In order to further reduce the system on-state loss and increase the switching frequency,Ga N devices of Ga N system are adopted,and an optimized driving circuit design method for the selected device s is proposed.At the same time,the parameters such as winding loss,parasitic capacitance and leakage inductance in the planar magnetic components are difficult to be predicted.Therefore,the influence of the structure of the magnetic components,the number of turns of the magnetic components and the number of layers,the thickness and width of the winding on the parasitic parameters are discussed.The precise design method of planar magnetic components is put forward,and the accuracy of the method is verified by finite element simulation with Maxwell simulation software.An optimized digital control method is utilized in this paper.Zero voltage signal detection and peak current detection are designed to determine the turn on and turn off moments of switches.The zero voltage opening of the switching device is realized,and the peak current of the switching device is effectively controlled and the stability of the system is improved.Moreover,constant current control method is also added to maintain output current constant,realizing the closed-loop control of the LED driving system.Because the state space averaging method neglects the parasitic parameters in the circuit and has some limitations,this paper adopts the circuit averaging method to model the non-ideal Buck circuit which works in the discontinuous current mode,and establishes its small signal model.And the system is compensated by hysteresis.At the same time,the optimized digital compensation strategy is proposed according to the corresponding difference algorithm,which improves the robustness of the system.Finally,a 60-W and 500 k Hz prototype was designed to demonstrate the theoretical analysis.The obtained power factor was as high as 0.98,THD was lower than 5%,and efficiency reached 92.9% at full load.The experimental results correspond with the theoretical analysis.