Unlike incandescent lamps and fluorescent lamps used in the past, their energy loss is large, but most of the energy is directly emitted by infrared rays, and the light source generates less heat. LEDs, in addition to being consumed as visible light, convert other energy. It became hot. In recent years, electronic products have gradually developed toward high density and high integration, and LED products are no exception. Therefore, solving the problem of LED heat dissipation has become a major problem in improving LED performance and developing the LED industry.
Reasons for LED heating:
The reason why the LED heats up is because the added electric energy is not converted into light energy, but a part is converted into heat energy. The luminous efficacy of LEDs is currently only 100lm/W, and its electro-optical conversion efficiency is only about 20~30%. That is to say, about 70% of the electrical energy becomes heat.
Specifically, the LED junction temperature is caused by two factors:
The internal quantum efficiency is not high, that is, when electrons and holes recombine, photons cannot be generated 100%, and it is generally called "current leakage" to lower the recombination rate of carriers in the PN region. Multiplying the leakage current by the voltage is the power of this part, which is converted into heat, but this part is not the main component, because the internal photon efficiency is now close to 90%.
The internally generated photons cannot be completely emitted outside the chip and finally converted into heat. This part is the main one, because the current external quantum efficiency is only about 30%, and most of it is converted into heat.
As mentioned above, although the incandescent lamp has a low light efficiency of only about 15 lm/W, it converts almost all of the electrical energy into light energy and radiates it. Because most of the radiant energy is infrared, the light efficiency is very low. But it eliminates the problem of heat dissipation.
LED heat dissipation solution:
Solving the heat dissipation of LEDs mainly starts from two aspects. Before and after packaging, it can be understood as the heat dissipation of LED chips and the heat dissipation of LED lamps. The heat dissipation of the Led chip is mainly related to the selection and process of the substrate and the circuit. This article mainly introduces the heat dissipation of Led lamps, because any LED will be made into lamps, so the heat generated by the LED chips will always be dissipated into the air through the outer casing of the lamps. If the heat dissipation is not good, because the heat capacity of the LED chip is small, a little bit of heat accumulation will cause the junction temperature of the chip to increase rapidly. If it is operated at a high temperature for a long period of time, its life will be shortened very quickly. However, there is a lot of way for this heat to actually lead the chip to the outside air. Specifically, the heat generated by the LED chip comes out of its metal heat sink block, first passes through the solder to the PCB of the aluminum substrate , and then passes through the thermal conductive glue to the aluminum heat sink. Therefore, the heat dissipation of LED lamps actually includes two parts: heat conduction and heat dissipation.
However, the heat dissipation of the LED lamp housing may have different options depending on the power level and the place of use. There are mainly the following cooling methods:
Aluminum fins: This is the most common way to dissipate heat, using aluminum fins as part of the enclosure to increase heat dissipation.
Thermally conductive plastic case: Fill the thermal conductive material during injection molding of the plastic case to increase the heat conduction and heat dissipation capability of the plastic case.
Air hydrodynamics uses the shape of the lamp envelope to create convective air, which is the lowest cost way to enhance heat dissipation.
The interior of the fan lamp housing uses a long-life and high-efficiency fan to enhance heat dissipation, resulting in low cost and good effect. However, it is more troublesome to change the fan, and it is not suitable for outdoor use. This design is rare.
The heat pipe uses heat pipe technology to conduct heat from the LED chip to the heat sink fins of the case. This is a common design in large luminaires such as street lights.
The surface radiation heat treatment treatment of the surface of the lamp housing is radiated and heat-dissipated. The simple application is to apply Zhisheng Weihua radiation heat-dissipating paint, which can radiate heat away from the surface of the lamp housing.
The following describes a new type of heat-dissipating coating: ZS-411 radiation heat-dissipating coating, which has high thermal conductivity and large heat-dissipating surface area, and has high emissivity in a relatively wide wavelength range (1-20μm). Significantly improved overall performance including conduction, convection, and radiative heat dissipation.
The heat dissipating solution has special properties such as high visible light and near-infrared light reflectance, high thermal infrared emissivity and stability, and also has good physical properties, chemical properties and good workability. The working principle of the heat-dissipating solution is to form a bonding force by agglomeration of inorganic colloidal particles (less than 100 nm). The addition of carbon nanotubes and other materials with high thermal conductivity and emissivity in the coating solution can make the surface of the coating exhibit a macroscopic, smooth and microscopic rough morphology of the nanomaterial component, which can greatly increase the contact area between the heat sink and the outside. Significantly improve heat dissipation. At the same time, a large number of spinels which have been electronically transitioned are added as composite infrared radiators, which not only increase the impurity level, but also improve the infrared radiation coefficient, and maintain the corresponding thermal stability and heat resistance.
In general, the luminous efficiency of LEDs is still relatively low, resulting in an increase in junction temperature and a decrease in lifetime. In order to reduce the junction temperature to improve the life, it is necessary to pay great attention to the problem of heat dissipation.
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