基于半峰宽的发光二极管结温测量方法

A Measurement Method Base on FWHM for Determining Junction Temperature of LED

设计了一种采用普通光谱仪,基于光谱半峰宽(FWHM)方法测量LED结温测试系统。首先采用普通光谱仪测量在不同环境温度和正常工作的驱动电流下各色LED的相对光谱分布,由于光谱仪采集到光谱数据均是离散的,为了得到较为精确的半峰宽,需要在最强峰值Imax一半即0.5Imax处附近将离散的光谱峰形数据拟合成连续的峰形函数,便可计算出在不同温度下较为精确的FWHM,再经过一定的函数拟合,得到结温Tj与FWHM的函数关系。实验发现白光和蓝光LEDTj-FWHM函数线性关系均高于其他颜色的LED,并且其线性指数R^2均非常接近1,表明各色LED其结温Tj和半峰宽FWHM两参量具有较强的线性函数关系;利用Tj与FWHM的函数关系,便可计算出任意测量值FWHM所对应的LED结温。由于该方法采用正常的驱动电流,自加热效应不可忽略,为了减少光谱仪在固定反应时间内由自加热效应而引起的LED器件结温的升高和温控系统引入的温度偏差而带来的测量误差,选定某状态下的Tj与FWHM为基准状态,并采用逐点作差法得到相应的ΔTj和ΔFWHM,再将ΔTj和ΔFWHM拟合成相应的线性函数,得到定标函数,这样极大地减少由自加热效应和温控系统而引入的偏差。最后将本方法得出的测量结果与采用Mentor Graphics公司的T3Ster仪器测出的结果进行了比较,发现偏离2.5%,在完全可接受的误差范围内。结果表明所提出的采用半峰宽法测量LED结温测试方法的可行性。该方法克服了光谱法的峰值波长漂移过小,对测试结果带来较大误差的缺点,并且具有不破坏原有封装结构和不需要昂贵仪器的优点。

In this paper,a measurement system based on the FWHM(Full Width Half Maximum)method for junction temperature of LED is designed,which uses ordinary spectrometer.First,the relative spectral distribution of various color LEDs under different ambient temperatures and driving currents are measured by a general spectrometer.Since the spectral data collected by the spectrometer are discrete,in order to obtain a more accurate FWHM,it is necessary to fit the discrete spectral data into a continuous peak near the half of the strongest peak value Imax,i.e.0.5Imax.So,the more accurate FWHM at different temperatures can be calculated and then the functional relationship between junction temperature Tj and FWHM can be obtained by fitting a certain function.Experiments show that the linear relationship between Tj-FWHM function of white and blue LED is higher than that of other color LED,and its linear index R^2 is very close to 1.It shows that the two parameters of Tj and FWHM have strong linear function relationship.Using the functional relationship between Tj and FWHM,the junction temperature corresponding to any measured value FWHM can be calculated.Because this method uses the normal driving current,the self-heating effect can not be neglected.In order to reduce the junction temperature rise of LED devices caused by self-heating effect in fixed reaction time and the measurement error caused by the temperature deviation introduced by temperature control system,Tj and FWHM in a certain state are selected as the reference state,and the corresponding Tj and FWHM are obtained by point-by-point difference method,and then the correspondingΔTj andΔFWHM are obtained.ΔTj andΔFWHM are fitted into corresponding linear functions to obtain the calibration function,which can greatly reduce the deviation caused by the self-heating effect and temperature control system.Finally,the results obtained by this method are compared with those obtained by T3 Ster instrument of Mentor Graphics.It is found that the deviation is 2.5%,which is within the acceptable error range.The results show that the proposed method of measuring the junction temperature of LED by the FWHM method is feasible.This method overcomes the shortcomings of small peak wavelength drift of spectroscopy,which brings great errors to the test results,and has the advantages of not destroying the original packaging structure and not requiring expensive instruments.