Thermal Design Ofa LED Multi-Chip Module For Automotive Headlights

Due to its advantages such as high luminous efficiency, low powerconsumption, long lifetime, high security and reliabilty, and no harm to environment,LED lighting is considered to be ideal as the4th generation of automotive headlightlighting source. However, heat dissipation is the bottleneck of its practicalapplication. The rise of LED chip junction temperature will cause many problemsincluding the reduction of both light output and lifetime.In this paper, a LED multi-chip module with a heat pipe was designed forautomotive headlights using the theory of thermal resistance, which took advantageof the relative air flow during vehicle travelling for forced convetion to keep thejunction temperature of LED chips below60℃. The structure is compact enough tobe suitable for placement in a small space for automotive lighting. The influence ofparaments on the junction temperature of LED chips, such as the distance of LEDarrangement and dimensions of both DBC substrates and sinks, has also beendiscussed by numerical simulation using ANSYS software. Then, the structure ofthe module was optimized. Three kinds of such modules with a heat pipe was made,all of which were cooled with forced air convection. The junction temperature wasmeasured using the forward voltage method, under the condition of both naturalconvection and forced convection. The differences among their thermalperformances were analyzed as well.It was pointed out that the composition of the module thermal resistance andcorresponding proportions. What’s more, it was analyzed that the factors having aneffect on convection thermal resistance, thermal contact resistance, thermalresistance of both LED chips and DBC substrates, all of which had an importantimpact on thermal performance of the module.Taking the condition of natural air convection during vehicle stopping intoaccount, a temperature control system was designed for the LED multi-chip module,whose fan was dominated by the feedback signal of fin temperature. The junctiontemperature of LED chips could be controlled within different ranges by settingdifferent threshold value of the system. Thus the junction temperature could beunder60℃.