Thermal Analysis In High Power LED And LED Arrays

Light emitting diode(LED) is a kind of semiconductor optical component with its merits of low operating voltage,energy saving,high luminous efficiency,more directional light source,non-pollution,long life expectancy and more design freedom, et al.It can be expected that HB-LED will become the fourth generation lighting source replacing incandescent and fluorescent.Due to the low luminous flux of one LED,it is a way to get high flux by mount several LED on a MCPCB.At present, thermal challenges must be resolved because of the low conversion rate of electricity-light.This thesis focuses on the thermal analysis of a kind of 5W white LED array which is used as house illumination.We study the issues such as junction temperature,thermal resistance and temperature distribution by two method:theoretic analysis,FEM simulation.First,we then discussed the produce of thermal,the character of thermal in LED and the thermal management.Meanwhile,LED arrays is brought forward and its thermal problem is introduced.Then the methods that are used to analyze thermal problem are discussed,especially the MARC FE software.A thermal resistance model is established.Inner and outer thermal resistance is calculated and the total is 7.623K / W.A 3D-model of classic high-power LED was established by using MARC,in which the heat distribution,thermal resistance,total deformation,Von-Mises strain and stress in steady and transient conditions were analyzed.Because the contact resistance was considered in FEM,the thermal resistance is 8.235K/W,which is a little bigger than the theoretic result.An improvement scheme that the heat path of LED isolates from the electric path is given.The result showed the thermal resistance of improved LED is 7.22K / W,which is about 1K / W smaller than the classic one. The simulation result shows that LED with natural convection can not operate at＞4.5W.Forced convection must be fitted to ensure the HP-LED structure quality. The LEDs array was also simulated in MARC.Due to the small space of the arrays, there are thermal coupling in LEDs,which caused the LED chip temperature rise.The effects of different LED array density,LED power density,and active versus passive cooling methods on device operation were calculated.Results showed that when heat conductance of the heatsink is higher than 300W / m·K,its thermal resistance is almost steady,so pursing high conductive heatsink material blindly is not a wise action.