Study On Heat Dissipation Of High Power LED Lamp

High power and high heating flux are inevitable trend of white color LED in lighting industry,however,the heat dissipation problem is the obstacle that prevent its further development.The main factors that affect the heat dissipation of high power LED are the chip package structure and proper external heat sink,therefore,it is of significant to study the heat dissipation problem from the chip level and system level.In this paper,we launched equivalent thermal path analysis aimed at Flip-to-chip,concluded that the substrate material layer is the key factor that affects the heat conduction.The FEM software ANSYS was applied to study on the heat transfer in the chip package structure,and verified the effect of three kind of substrate material that commonly used---sapphire,silicon and silicon carbide on chip thermal resistance,then the influence of different thickness of sapphire and silicon carbide as substrate material was simulated.The results indicated these materials correspond to the thermal resistance of chip form high to low as follow: Sapphire,silicon and silicon carbide.When the sapphire is used as the substrate,the thermal resistance decreases linearly with the substrate thickness,however,the thermal resistance of the chip is approximately parabola with the thickness of the substrate for silicon carbide.Through the simulation,the optimum thickness of the most suitable substrate material of the chip package is obtained from the angle of heat dissipation.A simplified physical model of heat dissipation was built for the purpose of researching whole street lamp,and then we launched equivalent thermal path analysis and built up mathematical model.The author suggested an innovative heat sink that combine traditional fin heat sink and micro heat pipe array,tested thermodynamic characteristic of MHPA experimentally,the expression of total thermal resistance of the new radiator was derived and parameters of heat sink were designed,finally concluded the calculation method of chip junction temperature.Optimal design of the new type heat sink was carried out,firstly,we selected the main factors affect the heat dissipation as the optimization variables,then set weight of heat sink and chip junction temperature as the optimization objectives,launched the optimization with Genetic Algorithm,finally got 4 groups of Pareto optimal solution.To verify the heat transfer capability of the optimized heat sink,we applied numerical simulation in ANSYS Icepak,and the contribution for heat dissipation was considered by changing local morphology on fins,results indicated that the optimized heat sink can ensure the lamp temperature maintain under 70℃,and demonstrate change of local morphology on fins could enhance convection effect and further decrease the working temperature of the lamp.In this paper,the settlement of heat dissipation problem of high power LED was studied through two technical routes: the package structure of LED chip and design of properly external heat sink,the author concluded optimal substrate layer material and its thickness from the point of heat dissipation,suggested an innovative external heat sink for LED street lamp,obtained outstanding heat dissipation effect as the simulation results indicated,and provided guiding suggestions for the research of heat dissipation of high power LED street lamp.