Reliability assurance of LED road lighting under low temperature operation environment

Along with the rapid development of LED lighting technology, in many domestic city, there is no lack of road lighting LED lamp shadow. Especially the high power LED device after the light effect of more than 100lm/W, the development trend of LED street lamp as road lighting has been widely recognized. In 2009, several domestic city were organized by testing evaluation of LED lighting products, LED lighting products most significantly in the light distribution system, light efficiency and other key technical indicators of progress, in the standard of road lighting and energy saving effect has reached the relevant standards and requirements. Despite the rapid development of the technology of LED street lamp, but most of the LED street lamp manufacturers in the product development process ignored the special technical requirements in the cold environment. A common misconception is that LED is conducive to heat dissipation in cold areas, not prone to failure. As everyone knows, the cold application environment, the LED lamp has a more stringent technical requirements, mainly in the following two aspects: (1) the cold area with low temperature and large temperature difference, thermal shock and sudden changes of the long-term low temperature for devices with more stringent quality requirements. (2) application of LED lights in the cold area must be considered to prevent the ice condensation prevention measures. In view of the above reasons, the application of LED street lamp in cold areas, the need to address the following key technical issues. The temperature change of cold shock may cause device failure due to LED LED chip package, which belongs to the solid solid state devices, there is a chip, silica gel (or resin), mismatch expansion coefficient between metal bracket and lead, coupled with the impact of hot and cold cold area of large temperature difference between the impact of changes in temperature will make the silica gel in the process of expansion and shrinkage, the device internal stress is too large, it will cause the LED wire bonding point displacement increases, lead to premature fatigue and damage. At the same time that the original solder bonding state of poor appearance may be caused by welding, solder ball and chip electrode sealing off phenomenon, and even make the LED chip failure phenomenon of layered shedding. A LED device of LED lights applications up to hundreds of pieces, usually by way of mixing in series based configuration, if a LED failure occurs, will cause a plurality of LED joint failure, so the application of LED lights in the cold area according to the first degree of lamp temperature under certain environment variation in characteristics of ultrasonic power set the reasonable bonding pressure, bonding time and bonding temperature and packaging process parameters, ensure the reliability of each LED device in low temperature operation environment. Another key technical challenge for the reliability assurance of the low temperature operation of the LED drive is the reliability of the LED street lamp driving device in the low temperature operating environment. Most of the current LED lamp drive power show phenomenon in different types of The climate does not suit one. in low temperature environment, the more prominent is the characterization of low temperature and long term operation at low temperature can not be started under the environment of the phenomenon of high failure rate. Is the main reason of these problems, the driving power at the design stage of the device selection without considering the reliability of low temperature working condition, characteristics of the key components of some low temperature changes caused by low temperature starting or driving device cannot run normally, the specific cause of the fault are mainly the following aspects: (1) the switch tube density and activity carrier at low temperature will decrease, overload protection will therefore reduce the starting point. (2) the electrolytic capacitor electrolyte is frozen at low temperature, and the capacitance effect is lost (the ion in the solution only has ion polarization at this time), and the carrying capacity is not available. (3) coupling device part type can not be normal in low temperature condition. (4) the input terminal to prevent the surge current of the thermistor, the resistance becomes larger at low temperature (3~5 times the normal temperature), it will cause the low temperature can not be activated. The solution of these problems is mainly from the choice of better temperature characteristics of the device. For example, not all of the electrolytic capacitor can work at low temperature in general, electrolytic capacitor above 200V low temperature tolerance is poor, and the electrolytic capacitor 160V the following basic can -40 C environment to work, as long as the choice of two low voltage electrolysis series can solve the problem. The device selection adjustment may slightly improve the drive cost, but from the overall cost of LED street view can be ignored, consider to improve the reliability and reduce maintenance cost factors, this adjustment is very necessary and worthwhile. A LED Street ice condensation protection measures be applied lamp harm it is easy to ignore in cold regions is due to snow in the surface of the lamp stack, formed after the ice started to melt ice, once formed, will have a large potential safety hazard to vehicles and pedestrians. Especially the LED street lamp, lamp shell is widely used because of aluminum, the surface of alumina is a hydrophilic material, more prone to ice condensation. In 2008, the South snowstorm in the vast areas of China, resulting in large aluminum surface high-voltage wire ice condensation, collapse damaged large power facilities. The consequences of this disaster is not only caused by the climate, alumina surface of the high-voltage cable is a hydrophilic material is an important incentive. Due to road traffic safety, thus preventing ice condensation is the safety measures must take into account the LED lamp applied in cold regions. In order to solve this key technology, we adopted the method of