Ideas for Solving the Problem of LED Display Heat Dissipation

How is the LED chip junction temperature generated?

The reason why the LED heats up is because the added electrical energy is not all converted into light energy, but a part of it is converted into heat energy. The light efficiency of LED 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 is turned into heat energy.

Specifically, the generation of LED junction temperature is caused by two factors. 

1. The internal quantum efficiency is not high, that is, when electrons and holes are recombined, photons cannot be generated 100%, which is usually referred to as "current leakage", which reduces the recombination rate of carriers in the PN region. The leakage current multiplied by the voltage is the power of this part, which is converted into heat energy, but this part does not account for the main component, because the internal photon efficiency is now close to 90%.

2.The photons generated inside cannot all be emitted to the outside of the chip and finally converted into heat. This part is the main part, because the current quantum efficiency called external is only about 30%, and most of it is converted into heat. Although the luminous efficiency of the incandescent lamp is very low, only about 15lm/W, it converts almost all the electrical energy into light energy and radiates it out. Because most of the radiant energy is infrared, the luminous efficiency is very low, but it eliminates the cooling problem. Now more and more people pay attention to the heat dissipation of LED. This is because the light decay or life of LED is directly related to its junction temperature.

High-power LED white light application and LED chip heat dissipation solutions

Today, LED white light products are gradually being put into use in various fields. People feel the amazing pleasure brought by high-power LED white light and are also worried about various practical problems! First of all, from the nature of high-power LED white light itself. High-power LED still suffer from poor uniformity of light emission, short lifespan of sealing materials, and especially the problem of heat dissipation of LED chips, which is difficult to solve, and cannot take advantage of the expected application advantages of white LED. Secondly, from the market price of high-power LED white light. Today's high-power LED is still an aristocratic white light product, because the price of high-power products is still too high, and the technology still needs to be improved, so high-power white LED products can not be used by anyone who wants to use them. Such as flexible LED display. Let's break down the related problems of high-power LED heat dissipation.

In recent years, with the efforts of industry experts, several improvement solutions have been proposed for the heat dissipation of high-power LED chips:

Ⅰ. Increase the amount of light emitted by increasing the area of the LED chip.

Ⅱ. Adopt package of several small-area LED chips.

Ⅲ. 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? In fact, it is striking! First of all, although we increase the area of the LED chip, we can obtain more luminous flux (light passing through a unit of time) The number of beams per unit area is the luminous flux, and the unit is ml).  It is good for LED industry. We hope to achieve the white light effect we want, but because the actual area is too large, there are some counterproductive phenomena in the application process and structure. 

So is it really impossible to solve the problem of high-power LED white light heat dissipation? Of course, it is not impossible to solve. In view of the negative problems caused by simply increasing the chip area, LED white light manufacturers have improved the surface of the high-power LED chip by encapsulating several small-area LED chips according to the improvement of the electrode structure and the flip-chip structure to achieve 60lm. /W high luminous flux and low luminous efficiency with high heat dissipation.

In fact, there is another method that can effectively improve the heat dissipation problem of high-power LED chips. That is to replace the previous plastic or plexiglass with silicone resin for its white light packaging material. Replacing the packaging material can not only solve the heat dissipation problem of the LED chip, but also improve the life of the white LED, which is really killing two birds with one stone. What I want to say is that almost all high power white light LED products like high power LED white light should use silicone as the encapsulation material. Why must silica gel be used as packaging material in high-power LED now? Because silica gel absorbs less than 1% of light of the same wavelength. However, the absorption rate of epoxy resin to 400-459nm light is as high as 45%, and it is easy to cause serious light decay due to the aging caused by long-term absorption of this short-wavelength light.

Of course, in actual production and life, there will be many problems such as heat dissipation of high-power LED white light chips, because the more extensive the application of high-power LED white light, the more in-depth and difficult problems will appear! The characteristics of LED chips are Extremely high heat is generated in a very small volume. The heat capacity of the LED itself is very small, so the heat must be conducted out at the fastest speed, otherwise a high junction temperature will be generated. In order to draw the heat out of the chip as much as possible, many improvements have been made on the chip structure of the LED. In order to improve the heat dissipation of the LED chip itself, the main improvement is to use a substrate material with better thermal conductivity.

Monitoring LED lamp temperature can also be imported into micro-controller

For the improved form of NTC power, if you want to achieve a better design, it is also a relatively pragmatic approach to carry out a more precise safety design with an MCU. In the development project, the status of the LED light source module can be divided into whether the light is Whether it is turned off or not, with the program logic judgment of temperature warning and temperature measurement, a more perfect smart lighting management mechanism is constructed.

For example, if there is a lamp temperature warning, the temperature of the module is still within an acceptable range through temperature measurement, and the normal way can be maintained to naturally dissipate the operating temperature through the heat sink. And when the warning informs that the measured temperature has reached the benchmark for implementing an active cooling mechanism, the MCU must control the operation of the cooling fan. Similarly, when the temperature enters the zone, the control mechanism should immediately turn off the light source, and at the same time confirm the temperature again 60 seconds or 180 seconds after the system is turned off. When the temperature of the LED solid-state light source module reaches a normal value, drive the LED light source again and continue to emit light.

sdd

Post time: Nov-09-2022

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