上海理工大学学报  2019, Vol. 41 Issue (4): 368-373 PDF

1. 上海理工大学 光电信息与计算机工程学院，上海 200093;
2. 常州工学院 光电工程学院，常州 213002

Characterization of the Average Junction Temperature of GaN-Based White LED Arrays by Centriod Wavelength
GUO Jie1,2, MA Junshan1, RAO Feng2, CHU Jing2
1. School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China;
2. School of Opts-Electrical Engineering, Changzhou Institute of Technology, Changzhou 213002, China
Abstract: The junction temperature is an important parameter that affects LED performance. It is of great significance to measure the junction temperature of LED quickly and accurately for the design and performance testing of LED products. Under different driving currents, the normalized spectral distribution of the GaN-based white-light LED arrays at different substrate temperatures was measured, and the centroid wavelength was calculated. The relationship between the centroid wavelength and the average temperature of the LED array was analyzed. The junction temperature of the array was measured and compared with that measured by the central wavelength method. The results show that there is a good linear relationship between the centroid wavelength and the average junction temperature, and the slope of the straight line changes exponentially with the change of the driving current. Compared with the central wavelength method, the accuracy of this method is higher. Therefore, using centroid wavelength to measure the junction temperature of the GaN-based white LED array is an intuitive, non-contact effective method.
Key words: spectroscopy     junction temperature measurement     spectral analysis     light emitting diode arrays     centroid wavelength

GaN基白光LED阵列平均结温的变化将导致每一波长对应的相对辐射强度发生变化，而质心波长、半高全款、光谱差异等特征参数与整个光谱分布相关。同时，在不同的驱动电流下，结温对光谱的影响程度不同。因此，可以建立光谱参数与阵列平均结温的关系。基于此，本文研究了采用质心波长表征GaN基LED阵列结温的可行性。

1 测量原理

 $\displaystyle{\lambda _{\rm c}}{\rm{ = }}\frac{\displaystyle{\int\nolimits_{{\lambda _1}}^{{\lambda _2}} {F(\lambda )\lambda {\rm{d}}\lambda } }}{\displaystyle{\int\nolimits_{{\lambda _1}}^{{\lambda _2}} {F(\lambda )} {\rm{d}}\lambda }}$ (1)

 $\frac{{{{\partial}} {\lambda _{\rm c}}}}{{{\rm {\partial}} {T_{\rm j}}}} = k$ (2)

 ${\left. {{\lambda _c}'} \right|_{I = {I_{\rm{0}}}}} = k\partial {T_{\rm j}} + {\lambda _{\rm c}}$ (3)

 ${T_{\rm j}} = \frac{{{\lambda _{\rm c}}' - {\lambda _{\rm c}}}}{{k(I)}} + T{}_0$ (4)

a. 测量给定小电流驱动、不同温度下的归一化光谱功率分布，计算质心波长 ${\lambda _{\rm{c}}}$ ，求出质心波长−平均结温系数k

b. 改变驱动电流，测量不同电流不同温度下的归一化光谱功率分布，得到一组随驱动电流变化的k，通过拟合得出不同电流下的电流修正公式为

 $k(I) = {\sigma _1}\exp \left( - \frac{I}{{{I_1}}}\right) + {\sigma _2}\exp \left( - \frac{I}{{{I_2}}}\right) + {\sigma _0}$ (5)

c. 计算待测条件下对应驱动电流Ik值；

d. 测量待测条件Tj下的归一化光谱功率分布，并计算质心波长 ${\lambda _{\rm{c}}}'$ ，结合初始温度T0下的质心波长 ${\lambda _{\rm{c}}}$ 和系数k，代入式（4）计算出待测结温Tj

e. 将不同方法的测量结果进行对比，得出该方法的适用性和准确性。

2 实　验

 图 1 测试系统结构图 Fig. 1 Schematic diagram of the test system

3 结果与讨论 3.1 白光LED阵列的归一化光谱功率分布

 图 2 单颗灯珠与串联阵列的归一化光谱功率分布 Fig. 2 Normalized spectral power distribution of a single bulb and a tandem array
3.2 恒定驱动电流时阵列质心波长与结温的关系

 图 3 质心波长随温度控制器温度的变化 Fig. 3 Variation of centroid wavelengths with the temperature of thermostat
3.3 不同驱动电流时阵列质心波长与结温的关系

 图 4 各驱动电流下的质心波长随温度控制器温度的变化 Fig. 4 Variation of centroid wavelengths with the temperature of thermostat under different driving currents

 图 5 质心波长–平均结温系数随驱动电流的变化 Fig. 5 Variation of average junction temperature coefficients of the centroid wavelength with different driving currents

3.4 测量精度分析 3.4.1 测量分辨率对比

 图 6 3种波长随热沉温度的变化 Fig. 6 Variation of three wavelengths with the heat-sink temperature
3.4.2 测量准确度对比

 图 7 3种方法测量结果比对 Fig. 7 Comparison of measurement results by three methods

4 结　论

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