LED is called the fourth generation of illumination source or green light source. It has the characteristics of energy saving, environmental protection, long life and small size. It can be widely used in various fields such as indication, display, decoration, backlight, general illumination and urban night scene. In recent years, some economically developed countries in the world have launched a fierce technical competition around the development of LED. Among them, LED heat dissipation has always been an urgent problem to be solved!
According to research data, if the illuminance of the LED chip is 50% when the junction temperature is 25 degrees, the luminescence amount is only 90% when the junction temperature rises to 60 degrees, and drops to 80% when the junction temperature is 100 degrees; 140 The degree is only 70%. It can be seen that improving heat dissipation and controlling junction temperature are very important things.
In addition to this, the heating of the LED will also cause its spectral shift; the color temperature will increase; the forward current will increase (at constant voltage supply); the reverse current will also increase; the thermal stress will increase; the phosphor epoxy aging accelerates, etc. All kinds of problems, so the heat dissipation of LEDs is the most important issue in the design of LED lamps.
How is the junction temperature of the LED chip generated?
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.
1. 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%.
2. 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.
Although the incandescent lamp has a very low luminous efficiency of only about 15 lm/W, it converts almost all of its electrical energy into light energy and radiates it. Because most of the radiant energy is infrared, the light efficiency is low, but it is exempted. The problem of heat dissipation.
The heat dissipation of LEDs is now more and more important to people. This is because the light decay of LEDs or their lifetime is directly related to their junction temperature. The heat dissipation is not good, the junction temperature is high and the lifetime is short. High-power LED white light application and LED chip heat dissipation solution
Today's LED white light products are gradually being put into use in various fields, people are feeling the amazing pleasure brought by their high-power LED white light and are also worried about the practical problems of their existence!
First of all, from the nature of high-power LED white light itself. High-power LEDs still have poor uniformity of illumination, and the life of the sealing materials is not long. Especially, the heat dissipation problem of LED chips is difficult to be solved well, and the application advantages of white LEDs cannot be exerted.
Secondly, from the market price of high-power LED white light. Today's high-power LEDs are still a kind of aristocratic white light products, because the price of high-power products is still too high, and the technology still needs to be perfected, so that high-power white LED products are not used by anyone who wants to use them. The following is a breakdown of the related issues of high-power LED heat dissipation.
In recent years, with the efforts of industry experts, several improvements have been proposed for the heat dissipation of high-power LED chips:
1. Increase the amount of luminescence by increasing the area of â€‹â€‹the LED chip.
2. It is used to package several small-area LED chips.
3. Change LED packaging materials and fluorescent materials.
So is it possible to completely improve the heat dissipation problem of high-power LED white light products through the above three methods? Itâ€™s awesome! First of all, although we increase the area of â€‹â€‹the LED chip, we can get more luminous flux (the amount of light per unit area of â€‹â€‹light per unit area is the luminous flux, the unit of ml), we hope to achieve the white light effect we want, but because of its actual The area is too large, which leads to some counterproductive phenomena in the application process and structure.
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