Investigation On Thermal Characteristics Of High Power White LEDs Device

High power LED, as a solid state lighting source with high energy conversion efficiency, is one of the most promising industrial products. Thermal analysis and management are a crucial problem in LED industrial chain from chip, packaging and lighting applications since LED devices are usually working in high power and high heat flux conditions. Based on this background, thermal investigation in LED chip, packaging and applications were conducted.The heat dissipation in LED chip design was considered by numerical simulation. The different factors that affect the heat transfer in chip were discussed. The results show that SiC substrate is better for chip heat dissipation. The thickness of chip substrate has great effect on the chip heat dissipation. When using sapphire and silicon as the substrates, thinner the chip substrate is, better the thermal performance will be. For SiC substrate, the thermal performance is the best when the substrate thickness is 0.04mm.Interface thermal resistance is one of the main thermal resistances in LED packaging. How to evaluate the thermal conductivity of the thermal interface material(TIM) is a big issue for decreasing interface thermal resistance. A transient hot-wire method were used to design a test equipment. Several TIMs were tested by the self-developed equipment. The results show that the measurement method is easy and the test results are credible.LED road lamp is one of the killer applications of high power LEDs. Thermal characteristics of an 80-W LED road lamp were studied. The averaging heat transfer coefficient of the fin heat sink used in LED road lamp were obtained by experiment, the temperature distribution of the fins were achieved by numerical simulation. A junction temperature estimation method was firstly provided based on the thermal resistance network. The temperature field of the fin heat sink was also calculated by an analytical solution based on thermal spreading resistance theory. Based on the analytical solution, temperature optimizations on the multi-chips packaging were conducted. The results show that optimized chip distribution is able to decrease the junction temperatures of chips and make the temperature uniform in fin heat sink. For extremely high power LED light sources, two kinds of active cooling solutions, honeycomb micro channel and closed micro jet heat sinks were firstly proposed. Experimental tests results on the two kinds of heat sinks show that both they can effectively dissipate the heat produced in LEDs to the ambient. Numerical simulation on the microjet cooler demonstrates that the microjet structure has great impact on the thermal and flow characteristics of the cooling system. The optimized structure can enhance its heat transfer and decrease its flow resistance. The decreasing of top cavity height can obviously increase the flow disturbance and heat transfer.