| LED lighting is replacing traditional lighting equipment such as incandescent lamps and fluorescent lamps with the advantages of high efficiency,long life and energy saving.In recent years,in order to improve the versatility of LED drivers,a LED driver is required to support different working voltage LED light sources,meaning that the LED driver need to support an as far as possible wide output voltage range.The traditional PWM-controlled hard-switching topology power supply has been unable to meet the requirement of current LED lighting equipment in terms of efficiency,volume,output power,and versatility.The soft-switching power supply with the advantages of simple circuit,high efficiency,long life and wide load variation range will be the future development trend of LED lighting driver.Nowadays,LLC topology is the most common soft-switching topology in medium and high power LED driver.However,the lower limit value of output voltage should not be lower than 50%at full load in constant current output mode.Otherwise,the resonator parameters designed under full load condition no longer meet the output requirements;In addition,the switching frequency varies widely when the LLC topology output voltage changes,so it is difficult to design the output filter.Through detailed analyzing the characteristics of LCC topology in constant current mode,it’s found that it can effectively overcome these shortcomings of LLC topology.But,there is no effective design algorithm for resonator parameters at home and abroad when LCC topology is applied in the field of medium and high power LED driver power supply.In order to achieve better results,engineers only depend on experience to repeatedly change the parameters of resonant cavity components,or even the number of transformer turns.On the basis of predecessors,this paper proposed a simple and effective design method to reduce the workload of engineers,shorten the product development cycle and reduce the cost of research and development.The main work of this topic includes the following points:(1)A brief analysis is made for traditional PWM control hard switching topology used in constant current output mode which shows the advantages and disadvantages of the topology in the application of LED driver.(2)Analyze and summarize the characteristics of series,parallel and LLC resonant topologies with their voltage and current gain characteristics.It was found that it could not meet the application requirements of current LED driver power supplies.(3)Based on the overall structure of the resonant converter,the differences between the half-bridge and full-bridge square wave generators and the characteristics of full-wave,full-bridge and double-current rectifier circuits are briefly analyzed.(4)Analyze the whole working process of LCC resonant topology in detail.It is found that the LCC resonant converter can ignore the influence of equivalent capacitance on the resonant cavity when the parallel resonant capacitor C_P capacity is much smaller than the series resonant capacitor C_r and the transformer primary winding N_P terminal voltage u_P can still be approximate as a square wave.Based on this feature,the first harmonic analysis method(FHA)is used to obtain the voltage and current gain characteristic curves.According to the characteristics of current gain curve,the optimal working area selection strategy is proposed,and the derivation process of the calculation formula of LCC resonant cavity and transformer parameters is given in detail.(5)According to the given input and output conditions,the resonant cavity parameters of the LCC resonant was calculated,the relevant waveforms were simulated by MATLAB,and then the whole circuit diagram with parameters was completed to design.At last,a 96W experimental prototype was produced and its relevant electrical parameters were tested to verify the rationality of the design method. |
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