【作者】 郝少华；

【导师】 叶邦彦；

【作者基本信息】 华南理工大学 ， 机械制造及自动化， 2010， 硕士

【摘要】 随着LED发光效率的提高,与传统光源相比,由于其节能、环保、响应时间短、体积小、寿命长等优势,越来越广泛地应用在背光源上。本文研究了大功率,高亮度的LED背光源,首先利用光学软件对光学系统进行设计与仿真,然后在光学设计基础上,对其进行热学分析,检验背光模组是否在额定温度下工作,以此简化系统设计的流程,缩短系统设计的周期。文章首先简单地阐述LED的发光原理及其特性,介绍白光LED的发光原理,并结合LED芯片封装结构的演变介绍目前国际主流白光封装技术,然后分析了LED结温对LED器件的影响。接着介绍了光学基本理论,光学建模的基本要素以及光学设计软件Tracepro的光线追踪原理和步骤,建立LED发光简化模型,研究了1W LED的光照度分布情况,接着推导出相应的光照度均匀分布公式。根据混光腔厚度的设计为20mm时,当背光源LED的间距20mm时光照度最均匀,并用计算机仿真模拟加以验证。然后推广到LED背光源阵列,光学均匀性达到95%。在保证相同光照度情况下,用3W的LED取代1W得LED,用计算机模拟,当LED间距为28mm,光学均匀性到85%,符合要求。然后介绍了LED中热的产生、热特性以及热管理、热问题的研究现状,同时介绍了光源模块及其热问题。指出ANSYS有限元分析软件在热分析中的应用。对要研究的对象建立了热阻模型,计算得到内部热阻为4.2999K/W,外部热阻为72.2367K/W,从而得到整个器件总热阻为80.691K/W。用数值模拟方法直观地显示了稳态条件下封装体内各个部分的温度分布,计算出的内部热阻为5.875K/W,与理论分析的结果比较接近。分析了热流密度矢量和温度梯度,接着模拟出LED内部的热应力分布,指出LED的内部应力在允许范围内。然后重分析了LED发热功率和对流交换系数对LED结温的影响。同时模拟了大功率LED光源模块的温度分布,由于各个LED之间距离较近,存在着热耦合现象,因此模块芯片比单颗芯片工作时结温高。同时分析了LED结温与分布间距之间的关系。然后模拟用3W LED取代光源模组,其温度也在额定温度下。文章最后设计了一个测温试验,并与理论、模拟分析的情况进行了对比,总结得出LED热分析的一种有借鉴意义的手段:通过简易方法测得特征温度,然后与模拟所得的关系式结合,进而分析得出结温和热阻。更多还原

【Abstract】 With the improvement of LED’s lighting efficiency, compare to the conventional light resource, due to its advantage of low power consumption, environmental protection, small volume, long lifetime and so on, it is widely used in back lighting of LCD screen. This paper researchs a kind of high power, high bright LED back light resource, firstly we use ray-tracing software to model and simulate the optical system, and then based on optical design ,analysis of the thermal state, we testify whether the back light module is working in the rated temperature.By these means, we simplify the system design process and shorten the time of the design.Firstly, the luminous principles of LED devices and electrode structure of the chip were presented; the principle of white light LED was introduced, and the current international mainstream of white packaging technology was also introduced with the situation of evolution of LED chip packaging structure, and then analyzed the impact of junction temperature to LED devices.Secondly we introduce the basic measure of basic test, the basic elements of optical modeling and the optical tracing theory and steps of ray-tracing software tracepro, establish the simplified optical model of LED, research the illumination distribution of 1W LED, and then derive the formula for illumination uniform distribution. According to the design, in the case of the thickness of light mixing cavity is 20mm, when the distance between the LEDs is 20mm, the illumination of backlight is the most uniform, and it is testified by the simulation. So extend to the LED backlight ray, illumination homogeneity can got reach to 95%. Under the same illumination, replacing the 1W LED with 3W LED, the spacing of LED is 28mm, which enable the uniformity reach to 85%.Then we discussed the heat produced in LED, its character of thermal and thermal management. Meanwhile, LED is brought forward and its thermal problem is introduced. Then the methods that are used to analyze thermal problem are discussed, especially the ANSYS FE software. We established a thermal resistance model for our object, and get the results of inner thermal resistance is 4.2999K/W, the outer is 72.2367K/W and the total is 80.691K/W. Heat distribution of the package at steady condition is showed by simulating. We get the result of thermal resistance, heat flow density vector and temperature grads. Inner resistance is 5.875K/W, which is closed to the result of the theoretic analyzed. Thermal stress distribution in the LED is also simulated, which is in the allowable range. We also analyzed the relationship between the junction temperature with LED heat power and the convection coefficient. The LEDs array was also simulated by ANSYS. Due to the small space of the arrays,there are thermal coupling in LEDs,which cause the LED chip temperature rise. The effects of different LED array density on device operation were calculated. Then we replace 1W LED with 3W, the result shows that the temperature is under the rated range.At the end of this paper, an experiment to test the temperature is carried out and the results are compared with that of simulation. We conclude an indicative method to deal with the thermal in LED: get a character temperature by a simple method, then combined it with the relations that concluded by simulating, at last, junction temperature and thermal resistance are gained.更多还原