Thermal Characteristics Measurement System Of High-power LED With Pulse Injection

In the field of semiconductor lighting, thermal characteristics is one of the most important factors affecting the overall performance of High-power LED. And the testing techniques for thermal characteristics have influenced each link of its development, design and production. With the development of semiconductor technology, more refined testing techniques and advanced testing equipments for thermal characteristics of the LED are required.At Present, the steady-state electrical parameters method has been widely applied in LED thermal properties testing, as it can achieve rapid measurement, simple operation, non-destruction,etc. Based on the theory of the electrical parameters method, the junction temperature and thermal resistance characteristics of LED are analyzed,and then the pulse method for measuring the junction temperature of the devices, and method for U-I curve are described.Finally, the thermal characteristics parameter measurement system based on pulse current is presented. Parameters needed in system detection are as follows:K-Coefficient with different pulse currents, AT(ie,temperature difference of the junction temperature of devices),and U-Icurves at different temperatures. The whole system is generally made up of two parts, respectively, the hardware and the software.The analog circuits and the digital circuits comprise the hardware system. And the main structure of analog circuits consist of three parts:the pulsed constant current supply module, the high-speed sampling module, and the temperature control module. The pulsed constant current supply is responsible for generating pulsed constant current with adjustable current values, changeable pulse period and width, so as to drive the LED. And the high-speed sampling module is used to detect positive junction voltage and current at each pulse peak. The temperature control module can achieve real-time checking and controlling of the temperature of devices. And the digital circuits consist of the microcontroller, FPGA, and the USB interface. STM32F107ARM chip as the core controller can connect and control all the peripheral devices. FPGA is used to generate modulated pulse and sampling pulse.USB acts as the connection between PC and the hardware system.The software system contains the computer applications and the embedded program of hardware. The computer applications based on VB6.0platform, is mainly responsible for the man-machine interface system operation and the data processing.The embedded program was re-edited on the foundation of msOS,ie,an architecture of open source embedded system.And it is used to receive command from PC, and control the entire hardware system to accomplish the whole measuring performance and finally return the data.In the end, the feasibility of the system is verified by analyzing and testing the main system parameters, and besides, performing some corresponding experiments.