Design And Implementation Of LED Photo-Electro-Thermal Test System Based On LabVIEW

Light-emitting diode(LED)has been widely used in various fields of social life as the result of energy saving,environmental protection,long life,small size,etc.In terms of energy saving,LED is the best choice to replace the current lighting source.For seeking higher brightness,many of the current LED lighting solutions encounter the undesirable chromaticity coordinate shifts owing to the heat generated by the higher power consumption.Therefore,it is necessary to analyze its photo-electro-thermal characteristics systematically to guide the design of the LED structure,furthermore,design higher-power LEDs without those drawbacks.The fundamental of LED photo-electro-thermal characteristics test is measuring junction temperature.Because of the LED chip size is tiny and the package of LED lamp,it is impossible to measure the junction temperature directly.To measure the junction temperature,forward voltage method is widely used.In traditional method,the junction temperature can be measured by the forward voltage due to the linear relationship.However,the pulse current is essential when the current soars which could lead to higher testing cost.This thesis summarizes the existing junction temperature test method,and the improved method is put forward.After that,a test system based on Lab VIEW is designed,it can measure the photo-electro-thermal characteristics automatically.This thesis tests four different LED lamp,analyzes their photo-electro-thermal characteristics systematically,as a result,the relationship between photo-electro-thermal characteristics can be obtained.The main work of this thesis is as follows:Firstly,this thesis proposes an improved test method based on forward voltage method for testing junction temperature.By fitting the relationship between voltage and temperature at low currents,the voltage-temperature relationship of any current is indicated,which furthermore lower the cost.Secondly,a test system based on Lab VIEW is designed in this thesis.It can not only test the relationship between the voltage but also the temperature,spectrum,luminous flux,luminous efficiency,etc.This test system automatically measures and saves the data to the local computer,which shorten the testing time and promote efficiency.Finally,by fitting the relationship between junction temperature,current and forward voltage,the corresponding junction temperature of the luminous spectrum can be obtained.With the increase of junction temperature,the intensity of the spectrum peak drop,and the wavelength of the spectrum peak floats to the blue.In addition,the luminous efficiency decreases along with the increase of the current.Through the analysis of MacAdam Ellipse,the chromaticity coordinate shifting is mainly blamed on the deviation of junction temperature rooting in different current.This test system designed in this thesis can test the LED photo-electro-thermal characteristics effectively,in addition,the improved forward voltage method can achieve low-cost testing of junction temperature.What's more,a systematically analysis method is put forward in this thesis.Through analyses,it can be learned that a feasible thermal structure can effectively reduce the junction temperature,furthermore,increase the luminous flux and the luminous efficiency in rated current,as a result,decrease the shift of chromaticity coordinate.