Light Emitting Diode (LED) is one of the most promising new cold light sources in the 21st century. The light-emitting mechanism of LEDs is that the electrons in the PN junction transition between the energy bands to generate light energy, and the chip has a fever phenomenon, especially a high-power LED, which is assembled into a module using a plurality of LEDs, and the heat dissipation is greatly increased. At present, only 15%-20% of the energy of LED is converted into light energy, and the remaining 80%-85% of the energy is converted into heat energy, and the chip size is only 2112.52.5mm, resulting in a large power density of the chip (up to 21). /Wmm magnitude). However, the heat dissipation of the LED device is relatively poor. First, because the infrared spectrum of the white LED does not contain the infrared portion, that is, its heat cannot be released by radiation; secondly, the diffusion heat resistance and the thermal resistance of the LED lamp are large. Poor heat dissipation can lead to serious consequences, such as reducing the light output of the LED, shortening the life of the device, and shifting the dominant wavelength of the LED. Therefore, how to make these thermal energy with the shortest path, the fastest method, and maximize the emission has become one of the key issues.
LED thermal management mainly includes three aspects: chip level, package level and system integration heat level. Among them, the chip is the main heating component, its quantum efficiency determines the heat efficiency, and the substrate material determines the heat transfer efficiency of the chip; for the package, the package structure, materials and process directly affect the heat dissipation efficiency; the system integrated heat dissipation level is also called the external The radiator mainly includes a heat sink, a heat pipe, a fan, a temperature equalizing plate and the like. In recent years, the problem of LED heat dissipation has been paid more and more attention by academic circles at home and abroad, and various researches have been carried out accordingly. However, since the heat dissipation of LED lamps is mostly empirical design, the heat dissipation system is relatively poor in professionalism, so that the heat dissipation problem of LED lamps is still very high. serious. Therefore, thermal analysis and thermal design of high-power LED lamps have important practical significance.
This paper first introduces the current heat dissipation technology of LED lamps and commonly used thermal analysis tools, then selects a high-power LED lamp as the research model, and uses ANSYS finite element analysis software to perform thermal analysis on the LED lamp to obtain various parts of the lamp. The temperature distribution and the maximum temperature of the chip are improved on the basis of this, and a satisfactory heat dissipation effect is obtained.
2 LED light cooling technology
At present, the main heat-dissipating technologies for high-power LED lamps include heat sinks, heat pipes, temperature equalizing plates, radiation coating layers, conductive pastes, and thermal conductive gaskets. The heat sink uses the enlarged surface area to dissipate heat convection into the environment. The factors affecting the heat dissipation performance of the heat sink are the shape of the heat sink, the number of fins, the pitch, the size, the tilt angle, the material of the heat sink and the processing technology. Commonly used heat dissipation technology, the model lamps in this paper use heat sinks to dissipate heat. The heat pipe uses the cyclic change of the condensed liquid phase to derive and dissipate the high heat generated by the LED. Under normal circumstances, the cold end of the heat pipe is used together with the heat sink to achieve better heat dissipation. The principle of the uniform temperature plate is similar to that of the heat pipe, except that the heat pipe is one-dimensional one-way heat transfer, and the uniform temperature plate is surface heat transfer, which has two-dimensionality, so that the surface temperature of the entire heat sink is uniform. The radiation coating layer is coated with a heat-dissipating paint on the outer surface of the heat sink to increase the emissivity and allow the heat to radiate more efficiently. The thermal paste and the thermal pad are designed to reduce the thermal resistance of the contact.
LED lamp heat dissipation defects mainly have the following four points:
1) The arrangement of heat sink fins of LED lamps is unreasonable. The arrangement of the heat dissipating fins does not take into account the use of the luminaire, affecting the heat dissipation effect of the heat sink, and designing the heat dissipating fins that conform to the characteristics of the product itself.
2) LED lamps over-emphasize the heat conduction link, but neglect the convection heat dissipation. Heat pipe, thermal grease and other heat-dissipating measures reduce the thermal resistance through heat conduction, but the heat ultimately depends on the outer surface area of the lamp, so it is a development trend to apply the radiation coating on the outer surface.
3) LED lamps neglect the balance of heat transfer. If the temperature distribution of the fins is severely uneven, it will cause some of the fins to have no effect or limited effect, and the uniform temperature plate can play a role in equalizing the temperature.
4) The heat dissipation of the luminaire is best to find the shortest design heat dissipation channel, so that the heat is released into the atmosphere as soon as possible. Among them, the interface thermal resistance is the bottleneck of the heat dissipation channel, so the focus of heat dissipation should also be placed on the interface thermal conductive material.