Research On Key Technologies Of Multi-characteristic Parameters Integrated Measurement System Of High-power LED

High power light emitting diodes(LEDs)are widely used in the field of general lighting due to their advantages of environmental protection,long life and high energy conversion efficiency.With the improvement of light efficiency,light intensity and circuit integration,the thermal problems of high-power LED devices become more and more serious.The accumulation of more heat leads to the increasing junction temperature and thermal resistance of LED,which leads to a series of reliability problems,such as the decline of optical output power,color shift,chip degradation and damage.As an important factor affecting the performance and reliability of high-power LED devices,the accurate measurement of junction temperature,thermal resistance and photochromic thermal coupling characteristics is very important to guide the thermal management optimization and heat dissipation design of highpower LED.In this paper,the comprehensive measurement of the optical,color,electricity and thermal multi characteristic parameters of high-power LED devices and the coupling characteristics analysis are taken as the objective.Aiming at the problems existing in the current measurement methods of thermal characteristics parameters of high-power LED,the improved measurement method of junction temperature and thermal resistance is proposed,and the design scheme of the comprehensive measurement system of high-power LED multi-characteristic parameters is proposed.Finally,the paper analyzes and verifies the multi group measurement experiments,and makes an exploratory study on the change law of the light color characteristics and thermal characteristics of high-power LED.The main work and conclusions are as follows(1)A method of voltage-down compensation junction temperature measurement based on reverse current is proposed.Firstly,the forward voltage(FVM)junction temperature measurement method is theoretically analyzed and deduced.After considering the effect of the measurement delay and abnormal temperature rise on the junction temperature measurement,the more accurate and complete data of junction temperature and transient cooling curve are obtained by introducing the switching process of compensating amount acceleration current and the combination of unbalanced carriers.(2)A differential difference fitting thermal resistance measurement method based on improved thermal interface is proposed.Firstly,the conventional transient double interface(TDI)thermal resistance measurement method is theoretically analyzed and deduced.Then,aiming at the problem that the separation point of TDI thermal resistance curve is not easy to determine and the measured value is low,the thermal resistance measurement value is more accurate by improving the exponential fitting of thermal interface and differential difference.Based on the optimized zth curve,the structure function analysis method is used to further obtain the thermal resistance value of each layer structure in high power LED.(3)An integrated measurement system for multi characteristic parameters of high-power LED based on LabVIEW is proposed.The accurate output of test current and the accurate measurement of junction temperature,thermal resistance and photochromic thermal coupling characteristics are realized.The program includes constant current source output control,K value calibration algorithm and transient thermal response measurement algorithm.(4)The variation of light color characteristics of high-power LED at different junction temperatures was studied.The proposed method and system are verified by a number of measurement experiments,and the influence of thermal characteristic parameters of high-power LED on its photochromic performance is analyzed.The preliminary research shows that the increase of junction temperature will lead to the significant decrease of luminous flux and luminous efficiency of high-power LED,resulting in the decrease of the peak value of the optical spectrum,the red shift of the peak wavelength and the blue shift of the main wavelength,the color temperature and chromaticity coordinates are shifted.In high temperature environment,the photochromic performance of high-power LED decreases sharply and tends to fail.