白光LED能量转换效率的研究

推导出了根据发光效能和光谱功率分布函数,计算了白光LED能量转换效率的公式,研究了1W白光LED能量转换效率与工作电流、环境温度和发光效能之间关系,并对荧光粉涂敷前后白光LED能量转换效率的变化进行了分析.研究结果表明,φ5、1W白光LED能量转换效率分别为22.67%和14.87%,1W白光LED的能量转换效率,随着工作电流、环境温度的增加而下降,能量转换效率与发光效能比值基本恒定,荧光粉涂敷前后白光LED能量转换效率从21.2%下降到15.11%,荧光粉能量转换效率约为93%.     

键合材料对1W白光LED性能的影响

对采用银浆和250℃、130℃度高、低温锡膏作为芯片键合材料的1W白光LED结温、热阻和光衰进行了对比研究。研究结果表明,与采用银浆作为芯片键合材料的LED相比,采用锡膏作为芯片键合材料的1W白光LED的结温下降了10℃以上,热阻也相应下降了约10K/W;两种键合材料的1W白光LED初始光通量基本没有差别,在光衰试验中,初期均存在光通量提高现象。在环境温度58℃时,工作1400h之后,光通量才开始小于初始光通量;在工作2880h之后,两种键合材料的1W白光LED光衰相差6%。     

基于积分宽度法测量发光二极管结温方法的研究

本文提出了一种基于光谱积分宽度法来测量发光二极管(light emitting diode, LED)结温的新方法,并进行了理论分析和实验研究。本方法主要分为光谱数据采集、定标函数的测定和结温测量三个过程。首先,为了测量成本的降低和精度的提高而采用在正常工作电流下采集LED光谱数据,并通过采用不同温度下的光谱积分宽度与选定的某一基准状态下的值逐差可得到线性度达0.99以上的定标函数,并通过此定标函数可实时测定任意状态下的结温。其次,为了比较本方法测量结温的精确性,分别对单色和白光LED采用本方法和业界主流的正向电压法,通过自行设计的基于积分宽度法结温测量系统和美国Mentor Graphics公司的T3Ster型仪器的测量结果进行比较,两种方法测出的结温最大偏差为2.1℃,在可接受的误差范围内。实验结果表明积分宽度法测结温具有高效便捷且低成本的的特点,具有一定的应用前景。     

一体化封装LED结温测量与发光特性研究

基于一体化封装基板,制备了大功率白光LED。以低热阻的一体化封装基板为基础,设计了结温测量系统。利用光谱仪测得不同结温下LED的光电参数,并对其机理进行了分析。在工作电流为0.34A,所研究温度范围为10.8～114.9℃。实验结果表明,一体化封装的LED结温与正向电压、光通量、光效和色温有着良好的线性关系;结温的变化对主波长及色坐标影响甚微;结温的上升导致蓝光段强度下降且光谱发生红移,黄光段强度上升且光谱发生宽化,峰值波长由450nm转为550nm。     

功率型白光LED可靠性的实验及仿真建模研究

快速推广LED产品到照明市场最主要的障碍在于长期的可靠性测试问题。由于长期的LED可靠性测试不符合快速且低成本的要求,因此本实验对白光LED进行步进式加速寿命老化测试,步进式环境温度从55oC到145oC变化。同时,对LED进行结温测试,并使用COMSOL仿真软件进行温度场分布仿真来模拟器件的发热情况,结果表明荧光胶处的温度高于LED芯片温度。在长期老化之后,对LED的光度进行测量,可以对LED的失效机理进行分析。通过研究温度对LED的光谱功率分布衰减的影响及光通量衰减的影响,发现在经过近3500 h的老化之后,LED的光衰很严重,表明电流及高温对LED的影响是极大的。     

如何确定大功率LED的工作电流

针对大功率LED应用,建立了大功率LED的热阻模型,分析了环境温度、器件的最大允许结温、热阻以及输入电流之间的关系,提出了一种保证器件结温低于容许最大结温的工作电流的确定方法,并给出了一个应用本方法绘制某大功率LED工作电流与环境温度的关系曲线的实例．本方法对大功率LED应用具有重要的指导意义。     

采用双光谱参数表征GaN基蓝色LED的结温

设计了一种采用双光谱参数表征GaN基蓝色LED结 温的新方法。采用光谱仪(OSA)测量不同环境温度、不同脉冲电流驱动下,GaN基蓝色LED的 光谱分布,先忽略脉冲电流的热效应,构建驱动电流、质心波长 、半高全宽(FWHM)和结温四者之 间的关系;然后利用该关系,结合实际点灯条件下LED的光谱分布,计算出对应的LED结温和 驱动电流。再根据统计 得到的GaN基蓝色LED脉冲电流-结温修正系数,对所得结温进行修正,得到考虑脉冲电流 热效应后更准确的LED结 温。研究表明,不同类型的LED脉冲电流-结温修正系数差别较小,当脉宽为2ms时,1W G aN基蓝色LED的脉冲电 流-结温修正系数为－5℃/A。与正向电压法相比,采用双光谱参数法得到的结温平均误差 约为2℃。因此,双光谱参数法可以 较准确地测量GaN基蓝色LED的结温。     

功率型LED热特性测试及评价

针对现有热特性测试及评价标准尚不完善的问题,以功率型发光二极管(LED)的精确热特性测试及评价为目标,采用光热一体化测试技术对不同的LED灯珠进行了热特性测试,研究了测试电流对K值标定及结温测试的影响,分析了热特性随环境温度的变化情况,提出了热性能测试及评价的合理建议。研究结果表明:测试电流对K值标定及结温测试有较大影响,测试电流的合理选取与芯片本身及功率的大小有关;材料的热导率随环境温度变化波动,对于某些高温使用环境,仅25℃的热性能参数数据并不能准确反应LED的热特性;热阻测试的准确性与光功率有关,光热一体化测试有利于得到准确的热特性数据。     

大电流冲击下MEH-PPV对白光LED发光特性的影响

针对用蓝光芯片激发YAG黄色荧光粉实现白光LED的光谱中缺少红色波段成份导致的显色性较差,通过在YAG荧光粉中混合质量分数分别为1%、3%、5%和10%的有机红光材料MEH-PPV,以提高白光LED的显色指数。将制备的白光LED加700mA冲击电流,通过对冲击前后光谱变化的分析结果发现,在大电流冲击下,由于散热不完善,PN结的热阻非常大,导致LED芯片快速老化,并且使有机材料MEH-PPV分解而大量失效;但是对比冲击前后黄光波段的光谱几乎没有变化。这表明,虽然MEH-PPV可以提高器件的显色指数,但是稳定性远不如YAG荧光粉。     

大功率LED的光衰机制研究

为了研究大功率LED的光衰机制,选用了一系列的大功率白光、蓝光发光二极管分别进行恒流点亮,在点亮不同时间阶段测量其光通量、发光谱及伏安特性.发现在光衰过程中,光通量有时会上升;通过LED光谱测定,发现光谱分布有明显变化;同时,pn结内阻也逐渐变大.研究表明大功率LED光衰有较为复杂的过程:其中荧光粉老化及pn结性能退化是最主要的.文章对此进行了初步的分析,为白光LED的应用及进一步研究白光LED衰减提供了参考.     

Effect of Different Quantum Well Structures on the Output Power Performance of GaN-Based Light-Emitting Diodes

We investigated the effect of two different quantum well (QW) structures having different indium contents on the optical performance of fully packaged GaN-based light-emitting diodes (LEDs). Dual-spectrum QW LEDs exhibit ～4% higher external quantum efficiency (at 350 mA) than single-spectrum QW LEDs. However, the two types of LEDs exhibit similar efficiency droop behavior. For both types of LEDs, the output power decreases with increasing junction temperature. When the junction temperature exceeds 70°C, the dual-spectrum QW LEDs exhibit lower output power than the single-spectrum QW LEDs. The wavelength dependence of the output power (at 350 mA) of single-spectrum QW LEDs shows that the LEDs with shorter wavelengths experience more rapid optical degradation than the LEDs with longer wavelengths. Based on the wavelength- and junction-temperature-dependent output power, the droop behavior of the dual-spectrum QW LEDs is described and discussed.     

Junction-temperature estimation in AlGaInP light-emitting diodes using the luminescence spectra method

This study proposes a practical method to estimate the junction temperature of AlGaInP LEDs using the luminescence spectra method. The peak wavelength shift of LEDs is due to the energy band gap shrinking. The temperature dependence of the bandgap of AlGaInP LEDs is derived from those of the underlying binary compounds AlP, GaP, and InP. Based on this, a theoretical model for the dependence of the peak wavelength on junction temperature is developed. Experimental results on the junction temperature of AlGaInP red light-emitting diodes are presented. Excellent agreement between the theoretical and experimental temperature dependence of the peak wavelength is found.     

DC Current-Induced Rollover of Illumination Efficiency of GaN-Based Power LEDs

Pulse drive currents were utilized to investigate dc current-induced rollover of illumination efficiency of GaN-based power light-emitting diodes (LEDs). By using the pulse drive currents, we can separate the effects that junction temperature and current injection have on dc current-induced rollover of illumination efficiency of GaN-based power LEDs. Comparing the measurement results obtained from pulse and dc drive currents, we verified that junction temperature and current injection were the major causes of dc current-induced rollover of illumination efficiency of power LEDs.     

Maintenance of stable light emission in high power LEDs

As well known, the light emission characteristics of the high power light-emitting diodes (LEDs) are very sensitive to the various driving conditions, especially the injected electric current and the junction temperature in operation. In this work, the dependency of the emission light from high power LEDs upon the driving electric current and the junction temperature will be explored in details. One integrated measurement system is proposed for the study in simultaneously obtaining all the thermal–optic–electric characteristics of LEDs throughout the measuring. Based on the basic feedback control methodology, one simple maintaining procedure is applied for the stable light emission in high power LEDs. It shows the robustness of the maintaining procedure from the environment change with the least heat dissipation in the operation of the high power LEDs. The results imply that all the thermal, the optic, and the electric properties of the high power LEDs should be taken into consideration in the same time rather than separately when maintaining their operation.     

大功率LED用封装基板研究进展

LED被称为第四代照明光源及绿色光源,近几年来该产业发展迅猛.由于LED结温的高低直接影响到LED的出光效率、器件寿命和可靠性等,因此散热问题已经成为大功率LED产业发展的瓶颈.文章阐述了大功率LED基板的封装结构和散热封装技术的发展状况,从基板的结构特点、导热性能及封装应用等方面分别介绍了金属芯印刷电路基板、覆铜陶瓷...     

倒装大功率白光LED热场分析与测试

散热是影响大功率LED正常工作及器件寿命的关键因素,本文利用有限元法(FEM)对W级倒装大功率白光LED的空间温度场分布进行了模拟计算,结果与用自制的测试装置测量的温度分布相吻合。在此基础上,保持电流密度不变,研究芯片尽寸与结区温度的关系,计算出在当前的发光效率和封装结构条件下,由于散热条件的限制,芯片能承受的最大功率和能达到的最大尺寸。     

功率LED结温和热阻在不同电流下性质研究

通过对不同驱动电流下各种颜色LED结温和热阻测量,发现各种颜色LED的热阻值均随驱动电流的增加而变大,其中基于InGaN材料的蓝光和白光LED工作在小于额定电流下时,热阻上升迅速;驱动电流大于额定电流时,热阻上升速率变缓。其他颜色LED热阻随驱动电流变化速率基本不变。结温也随驱动电流的增加而变大。相同驱动电流下,基于AlGaInP材料的1W红色、橙色LED的结温要低于基于InGaN材料的蓝色、绿色、白色LED的结温。分别用正向电压法和红外热像仪法测量了实验室自制的1 mm×1 mm蓝光芯片结温,比较了两种方法的优缺点。结果表明,电学法测量简单快捷,测量结果可以满足要求。     

A study on the heat dissipation of high power multi-chip COB LEDs

In this study, the heat dissipation efficiencies of high power multi-chip COB (Chip-on-Board) LEDs with five different chip gaps were compared by assessing their junction temperature (T_j) and thermal resistance (R_th). Junction temperatures were measured using an IR camera and were also simulated by computational fluid dynamics (CFD) software. The effects of heat sinks with different surface areas, heat slugs made of different materials and different injection currents (different wattages) on high power LED junction temperatures are discussed. In addition, the optical characteristics of the LED, such as its lumens and luminous efficiency are evaluated. The experimental results show that a chip with a smaller gap has a higher junction temperature and more thermal resistance, and the junction temperature difference between the LEDs with the smallest and largest chip gaps is 3.12 °C. Optical performance analyses show that the LED with a larger chip gap has higher lumens and higher luminous efficiency. Thus, higher junction temperatures reduce the optical performance of high power LEDs.     

大功率LED灯合成双射流主动散热费用模型研究

针对合成双射流激励器大功率LED灯主动散热方案,利用Ansys软件对LED灯模型在表面射流不同流速下的散热进行仿真,并结合试验结果验证,得到气体流速和pn结温度的散点图,利用Matlab进行Gauss曲线拟合,得到pn结温度与射流速度的关系;利用阿伦尼乌斯(Arrhenius)加速模型对pn结温度与LED灯寿命的关系进行预测,得到LED灯寿命与pn结温度的一般数学关系,进而得到LED灯寿命与合成双射流流速的数学关系,结合LED灯的经济性要求,建立了基于合成双射流的LED灯散热的费用模型;通过费用模型寻找最优解,可以确定LED灯单位时间最小费用及相应合成双射流最佳速度和LED灯寿命。