Research Of The Electrolytic Capacitor-less High Power LED Driver Circuit Based On Soft-switching Technology

With the increasing tension of the world's energy, more and more attention has been paid on the high efficiency and energy saving light sources. Based on the advantages of greater lighting efficiency, environmental protection, energy saving, high reliability and life long and so on, LEDs are widely used in various lighting applications, where one of the most important applications is street lighting. As a novel LED driver for street lighting, its performance index usually require electrolytic capacitor- less, high power factor, high efficiency, current balancing and so on. However, if the above characteristics need to be achieved, the structure of the LED driver will become more complexity, which will increase the cost and reduce the possibility of practical application.In view of the problems of high power LED driver, this paper proposes a electrolytic capacitor-less high power LED driver circuit based on soft switching technology. The driver is composed of two stages. The first stage is the traditional Boost circuit. The high power factor and the output voltage ripple reduction can be achieved by operating at the DCM mode and adopting the method of injecting the third harmonics into the input current, respectively. The second stage is the innovative LLC resonant circuit, aiming to realize the soft-switching technology and the current balancing of four LED strings. In order to get a constant output current, this paper introduces the PFM closed loop control strategy based on uc3863. Because the output voltage ripple of first stage is small and the second stage uses the closed loop control strategy, the driver can addopt the CBB capacitors instead of electrolytic capacitors. The main works of this paper are:(1)The research status on LED driver at home and abroad is analyzed, where this paper summarizes the performance of the novel high power LED driver.(2)The basic theory of power factor is analyzed, and this paper demonstrates why the Boost circuit can achieve PFC by operating in DCM mode, in detail.(3)The operation principle of the method, injecting the third harmonics into the input current, is described, and the Boost circuit is simulated and analyzed.(4)The operation principle of the LLC current balancing resonance circuit is analysed in detail, and this paper explains why the LLC circuit can make the technology of soft-switching and current balancing come true.(5)The control algorithm based on uc3863 aiming to realize output current constant is presented in this paper, and the simulation of LLC current balancing resonant circuit is given.(6)The electrolytic capacitor-less high power LED driving circuit based on soft switching circuit is designed based on the performance index given in this paper, and its main parameters are demonstrated and calculated.(7)The simulation circuit based on Saber software is established, and the LED driver prototype of the four channels whose rated power and current is 96 W and 0.6A separately is completed. Finally, the simulation results and the experimental results are analyzed in detail.Simulation and experimental results show that the driver can achieve the performance index given in this paper, which proves the feasibility of the electrolytic capacitor- less high power LED driver based on soft switching technology.