Treatment measures of high-power LED street lamp under extremely cold environment

The application of high-power LED street lamps in icy regions needs to deal with the following key technical issues.

1. The temperature change of hot and cold shocks may cause the failure of LED devices

After the LED chip is packaged, it is a solid solid device. There is a mismatch in the shrinkage coefficient between the chip, silicone (or resin), metal bracket and lead, plus the impact of cold and hot shocks with a large temperature difference in the cold area In the process of temperature change, silicone rubber shrinks and shrinks, and the internal stress of the device is too large, which will lead to increased displacement of the LED wire bonding point, premature tire fatigue and damage. At the same time, the solder joints that are originally in a poor bonding state may be de-soldered, and the phenomenon of de-soldering the solder ball and the chip electrode will cause the LED chip to exhibit a layered failure.

There are hundreds of LED devices used in an LED street lamp , usually in a series-connected hybrid configuration mode, assuming that one LED has a defect, it will cause multiple LEDs to fail together, so it is used in LEDs in icy regions The street lamp must first set reasonable packaging technology parameters such as ultrasonic power, bonding pressure, bonding time and bonding temperature according to the temperature change characteristics of the lamp under a specific application environment to ensure the reliability of each LED device under low-temperature operating environment .

Second, the reliability of LED driver installation at low temperature

Another key technical challenge lies in the reliability of LED street lamp drivers installed in low-temperature operating environments. At present, most LED street lamp driving power shows different types of soil and water dissatisfaction in cold areas and low temperatures. The more prominent characteristics are the failure to start normally at low temperatures and the high failure rate in long-term low-temperature operating environments. The main reason for the above problems is that the device selection of the drive power supply at the design stage does not consider the reliability of the low-temperature working state, and the characteristics of some key components in the low-temperature environment have changed. The meticulous reasons mainly include the following four aspects:

First, the density and activity of the switching tube will be reduced at low temperature, and the starting point of overload maintenance will also be reduced; second, the electrolytic capacitor electrolyte will freeze at low temperature and lose the capacitance effect (the ions in the solution are now There is only ion polarization), no load ability; third, the local type of optical coupling device can not work normally at low temperature; fourth, the thermistor at the input terminal to avoid inrush current, the resistance value becomes larger at low temperature ( 3 to 5 times the normal temperature ), it will also constitute a low temperature can not start normally.

The way to deal with the above problems is to start with the selection of devices with better temperature characteristics. For example, not all electrolytic capacitors cannot work at low temperatures. Generally speaking, electrolytic capacitors above 200V have poor low-temperature resistance, while electrolytic capacitors below 160V can work normally at minus 40 degrees Celsius . A series of low-pressure electrolysis can solve the problem. The adjustment of device selection may slightly increase the cost of driving installation, but from the perspective of the overall cost of LED street lamps, it can be neglected, and it is necessary and cost-effective to consider the factors of improving reliability and reducing maintenance costs.

3. Protection measures for LED street light icing

One of the problems that is easily overlooked when street lamps are used in icy regions is that ice and snow accumulate on the surface of the lamps, and the ice icicles formed after being heated and melted. Once the ice icicles are formed, it will cause a great potential safety hazard to vehicles and pedestrians. Especially for LED street lamps , aluminum is generally used for the lamp housing, and the appearance of aluminum oxide is hydrophilic, which is more likely to cause ice condensation. In 2008, a large-scale snow disaster in southern China constituted a large amount of ice icing on aluminum exterior high-voltage conductors, which collapsed and destroyed a large number of electrical equipment. The consequences of this scourge are not limited to climate, and the high-voltage cost cables of alumina appearance are hydrophilic materials and an important incentive. Because it affects the safety of road traffic, avoiding ice condensation is a necessary safety measure for LED street lamps in icy areas.

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