Estimation And Control Of The Junction Temperature Of LED Automotive Lamps

As the fourth generation light source,LED has been widely used in the field of automotive lighting because of its advantages such as high light efficiency,long life,fast response,small size and good shock resistance.During LED work,more than 70% of the electric energy is converted into heat.If heat dissipation is not well,the LED junction temperature will be excessive,which will lead to the reduce of LED light effect,significantly reduce of the lifetime.In this paper,the optimal design and control of the junction temperature in the LED automobile lamps are discussed by experiment and simulation analysis.The main work includes the following parts.The precondition of optimize and control LED junction temperature is measure the junction temperature fast,accurately and real-time.Therefore in this paper a new method is proposed to measure the LED junction temperature by using the function model between the junction temperature Tjn and the surface temperature Ts1.The method is as following.Firstly,a high-speed current switching device and LED junction temperature measuring system is build,using the forward voltage method to measure the LED junction temperature;Measure the LED surface temperature through Infrared thermal imager.Then derive the function between the LED junction temperature and its surface temperature by fitting the testing data,and modify the Tjn-Ts1 function according to the finite element model simulation results.Finally,the LED junction temperature can be obtained through the function and real-time LED surface temperature.The test results show that the error of LED junction temperature measured by this method can be controlled within 1.5?.The small and medium power automotive LED light has no dissipate heat system,so in this paper,taking the daytime running light of medium power as an example,an optimal design method was presented to control the temperature of the LED automotive light based on the thermal analysis.Firstly,the LED daytime running light was modeled by COMSOL software.And an experiment was carried out to acquire the distribution of temperature on the surface of LED DRL.Then based on the model,the relationships between LED junction temperature and the interval of LEDs,and thickness of MCPCB were discussed detailed.Finally,considering the costs,the optimal design of the LED DRL is presented by the proposed design method.High power LED automotive head lights produce greater heat,and it's close to the engine cause high ambient temperature,the traditional radiator cooling effect is limited,so the LED junction temperature control system based the semiconductor refrigeration chips is discussed in this paper.Firstly,a hardware system,including a one-ampere constant current LED driver and the control circuit of the semiconductor refrigeration chips,are build.Then a software with the delay PID algorithm are developed in Simulink to control the B&R PLC controller and the thermocouple sensor.Finally,the real-time temperature of the LED lamp are input to the software,and the output is set to control the semiconductor refrigeration chips,which decrease the junction temperature of LED.The control system can decrease the temperature of 10 w LED pin to 25? in 50 s,at this time,the junction temperature is about 80?,which keeps the LED automotive head lights working normally and safely.