There are some misunderstandings about the perception and use of infrared LEDs. The most important ones are:
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First, the importance of heat dissipation is neglected: we often use a heat sink that is too small or does not use a heat sink at all. It should be known that poor heat dissipation can result in high operating temperature of the chip and a decrease in infrared wavelength and a decrease in photoelectric conversion efficiency. The wavelength is higher than 850nm, which causes the camera CCD to deteriorate the light, that is, the night vision effect is worse. Low photoelectric conversion efficiency means insufficient brightness. Often a few cents of heat sinks will produce a big effect of small soldiers.
Second, the wrong hand touch to test the temperature: often someone was shocked by himself, because the human hand placed on the shell (or heat sink) more than 44 degrees Celsius, less than 2-3 seconds can not stand, so I feel "Too hot", in fact, this temperature is not high, and will not harm the normal operation of electronic components. Moreover, the higher the temperature of the outer casing (or heat sink) is, the better the "hot" is derived. "Energy is not extinguished"---Imagine: the outer casing (or heat sink) is not hot, this "hot" goes there? The heat stays on the chip and can't be guided, which causes the chip to work at high temperature, night vision effect The difference is that the light decay is large and the life is short.
Third, think that larger chips will be relatively small "bright": therefore, blindly specify LEDs that require large-size chips. Be aware that the brightness depends on the current. How much current can be used? It depends on the heat dissipation process. That is, the heat determines the current and determines the brightness. The size of the chip determines the brightness. In theory, regardless of the size of the same brand of chip, if the current and voltage are the same (power is the same), the heat generated is the same. The question is: how much heat is scattered in the same area? It is scattered in the size of the pinhole. The size of the area, the difficulty of heat treatment is greatly different. In terms of heat dissipation, each company has different technologies, different equipment, and different heat dissipation materials. Therefore, the ability of each family to dispose of the same "hot" on a large area is different.
For example: If the current of 1.2A is provided on the 28mil chip and the 42mil chip, the voltage is slightly the same (about 1.7V), so the power is slightly the same (about 2W). Of course, the heat generated is also the same. The problem is: Dissipating this 2W of heat on the area of ​​the 42mil chip is easier to handle, and it is more difficult to spread it on a 28mil chip. The packaging method using traditional silver glue to "solid crystal" has a thermal resistance of generally 20 ° C - 30 ° C / W, and is packaged using eutectic technology, and the thermal resistance is generally 6 ° C - 10 ° C / W, which Explain that the heat dissipation effect is completely different. The drive currents that can be used in the above two are greatly different, and the brightness varies greatly.
Of course, the use of advanced heat dissipation technology and small chip package, high current drive method is also limited. If the above 2W heat is placed on the area of ​​10 mil chip, even if it is packaged in eutectic process, it is difficult to smoothly and completely heat. Export. I hope that in the future, after the heat-dissipation technology and materials are improved, it is possible to realize a more advanced infrared LED with a smaller chip and a lower price, but the night vision effect remains the same.
In summary: the night vision effect of a large-sized chip is not necessarily stronger than that of a small-sized chip, and the end-to-side heat treatment is determined. Therefore, the packaging technology of the eutectic process is one of the important means of current cost performance improvement, and it should also be the future trend.
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