LED street light fixture Manufacturer is known as the fourth generation or green light, energy saving, environmental protection, long life, small size and other characteristics, can be widely applied in various directions , display, decoration , backlight, general lighting and urban landscape and other fields. In recent years, some of the world 's developed economies around the development of LED technology in a fierce competition . LED heat which has been a serious problem !
Research data indicate that if the LED chip junction temperature of 25 degrees when the light emission is 100% , then the junction temperature rises to 60 degrees , the light emission amount is only 90% ; junction temperature of 100 degrees dropped to 80% ; 140 degree is only 70%. Visible improve heat dissipation , junction temperature control is a very important thing.
In addition to the LED heat also makes its spectral shift ; color temperature increases ; forward current increases ( constant supply) ; reverse current increases ; thermal stress increased ; phosphor epoxy accelerated aging , etc. problems , so that the heat LED LED lighting design is the most important issue .
LED chip junction temperature is how to generate the
LED heat added reason is because not all the energy into light energy , but part transformed into heat. LED light efficiency is currently only 100lm / W, its electro-optical conversion efficiency of only about 20 to 30%. That is about 70% of the electrical energy into heat .
Specifically , LED junction temperature is generated caused due to two factors .
1 . Internal quantum efficiency is not high , that is, when the electron and hole recombination , and can not produce 100% of all photons, commonly referred to as the " current leakage " of carriers leaving the PN zone composite rate. Leakage current times the voltage that this part of the power , which is converted into heat , but this part does not account for the main component , because the internal photon efficiency is close to 90%.
2 . Internally generated photons emitted to the outside of the chip can not be fully converted to the final heat, which is the main part , referred to as the current that the external quantum efficiency is only about 30% , most of the heat is converted into a .
Although incandescent light efficiency is very low , only 15lm / W or so, but it is almost all the light energy is converted into electrical energy is radiated , since most of the infrared radiation is therefore very low efficiency, but eliminates the problem of heat dissipation .
Cooling LED is now more and more people pay attention , because the LED light failure or life is directly related to its junction temperature , heat is not good junction temperature is high , life is short . High-power LED white LED chip cooling applications and solutions
Today white LED products are increasingly used in various fields and put into use , people feel the amazing power LED white light brings pleasure while also practical issues to worry about its existence !
First, from the very nature of high-power white LED . High-power LED still exists luminous uniformity is poor , life is not long enclosed materials especially its LED chip cooling problem is difficult to get a good solution , but can not play the advantages of white LED applications are expected.
Second, from the high-power white LED street light fixture Manufacturer is . Today's high-power LED or an aristocratic style of white products , power products because the price is still too high , but technically still needs to be improved , so that the high-power white LED products not who wants to use it can be used . The following issues related to decomposition under high-power LED heat dissipation .
In recent years the efforts of industry experts for high-power LED chip cooling issues raised the following points to improve the program :
1 by increasing the LED chip area to increase the amount of light emitted .
(2) using several small area LED chip package .
3 . Changing LED packaging materials and fluorescent materials.
It is not by these three methods you can completely improve the heat dissipation problem of high-power white LED products out? Actually striking ! First we though the LED chip area increases, in order to obtain ( within a few beams of light per unit area per unit time is the flux through the unit ml) hopes to achieve more luminous flux white effect we want, but because the actual too large , resulting in the opposite phenomenon occurs in some application process with structure.
It is not white power LED thermal problems really can not solve it? Certainly not impossible to solve. Simply increasing the chip area for the emergence of negative issues , LED white light industry are the purposes of the electrode structure improvement and flip chip packaging structure and use several small area LED chips and other ways to improve from a high-power LED wafer surface thereby to achieve 60lm / W high low High heat flux luminous efficiency.
In fact, there is a way to effectively improve the heat dissipation problem of high-power LED chips . That is, it replaces the previous white plastic packaging materials or plexiglass with silicone . Replace the packaging material is not only able to solve problems more LED chip cooling can improve white LED life , really double-edged sword ah. I want to say is that almost all high-power LED white light such as high-power white LED silicone products should be used as a packaging material . Why are high-power LED silicone must be used as a packaging material ? Because the wavelength of light for the same silica gel absorption rate of less than 1% . But epoxy to light of 400-459nm absorption rate up to 45% , it is easy to produce due to the long aging absorb short-wavelength light after leaving the light of this serious decline .
Of course, there will be a lot of problems such as high-power white LED chip cooling in the actual production life, because people more extensive application of high-power white LED appears more deeply intractable problems ! LED chip features a high heat is generated in a very small volume . The heat capacity of the LED itself is small, it must be the fastest of these heat conduction out , otherwise you will have a very high junction temperature. In order to maximize the heat leads to the outside of the chip , the people on the LED chip structure has been a lot of improvements. In order to improve the heat dissipation of the LED chip itself , its main improvement is the use of better thermal conductivity substrate material . Like Cree 's LED thermal resistance because the use of silicon carbide as the substrate , the thermal resistance than other companies at least twice as low .
Even if it can solve the thermal resistance from the chip to the package material between , but the cooling effect from the package to the PCB board is not good , it is also caused by the LED street light fixture Manufacturer rises , the phenomenon appears luminous efficiency decreases . So, like the Panasonic just to solve this problem , starting in 2005 , he gave including circular , linear, surface -type white LED, and PCB board design into one, to overcome possible because of the emergence from the package to the PCB board interruption between the heat problem .
Thus , in the face of constantly improving the current situation , while how to increase the heat capacity is urgent at this stage to be overcome, in every sense , in addition to the material itself, but also included among the packaging material from the wafer heat resistance , heat resistance thermal structure, packaging materials to the PCB board between thermal structure, and the PCB thermal structure , all of which needs to be holistic considerations.
More info you can visit:http://www.lead-lighting.com/products/sid108-1.htm
没有评论:
发表评论