Engineer experience: Summary of five misunderstandings and solutions for LED heat dissipation

　　With the widespread application of LEDs, LED heat dissipation issues are receiving more and more attention. The heat dissipation performance of LEDs will directly affect the life of LED products. Therefore, it is imperative to solve the heat dissipation problem of LEDs. This article analyzes several misunderstandings about LED heat dissipation and shares some solutions to the problem of LED heat dissipation. I hope it will be helpful to everyone.

　　1. Analysis of Misunderstandings of LED Heat Dissipation

　　The misunderstandings of LED heat dissipation are mainly reflected in the following aspects:

　　1. The internal quantum efficiency is not high. That is, when electrons and holes recombine, photons cannot be generated 100%, which is usually called "current leakage" and 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 the chip cannot all be emitted to the outside of the chip and are finally converted into heat. This part is the main one, because the current so-called external quantum efficiency is only about 30%, and most of it is converted into heat.

　　3. Over-reliance on thermal conductive materials. Because any high-tech material can dissipate heat. In fact, using ordinary aluminum for heat dissipation, after multiple tests, the temperature of the heat sink is only 3-5 degrees Celsius higher than the bottom of the radiator. In other words, if a material with excellent thermal conductivity can be used, the temperature can be reduced by 3-5 degrees Celsius when the thermal resistance is zero.

　　4. Superstitious belief in heat pipes. There is no doubt that heat pipes have good thermal conductivity. But the heat from the heat sink must eventually be taken away by air convection. If there are no heat dissipation fins, the heat pipe will quickly reach thermal equilibrium, and the temperature will rise together with the heat sink. If heat dissipation fins are added to the heat pipe, the fins will still be used to dissipate heat in the end. Moreover, the contact point between the fins and the heat pipe is not as good as other contact methods. The result is that the cost is high and the heat dissipation effect is not improved. However, heat pipes are still useful for heat conduction on integrated LEDs, but the structure must be reasonable!

　　5. Trusting the nano-radiation materials promoted by some manufacturers. The proportion of radiation heat dissipation can be ignored when the temperature of the current LED lamp is around 50 degrees Celsius. Even if the radiation coating promoted by the manufacturer has a good radiation effect as they advertise, even if it reaches the radiation capacity of black body radiation, its heat dissipation proportion is only a few percent. Moreover, the coating itself will hinder the heat dissipation, thus affecting the heat dissipation by convection.

　　2. Solutions to LED heat dissipation problems

　　Next, let’s take a look at how to deal with LED heat dissipation issues.

　　Method 1: Aluminum heat sink fins

　　This is the most common way of heat dissipation, using aluminum heat sink fins as part of the outer shell to increase the heat dissipation area.

　　Method 2: Thermally conductive plastic shell

　　Using LED insulating heat dissipation plastic instead of aluminum alloy to make the heat sink can greatly improve the heat radiation capacity.

　　Method 3: Air Fluid Mechanics

　　Utilizing the shape of the lamp housing to create convection air is the lowest cost way to enhance heat dissipation.

　　Method 4: Liquid Bulb

　　Liquid bulb packaging technology is used to fill the bulb with a transparent liquid with high thermal conductivity. This is the only technology that uses the light-emitting surface of the LED chip to conduct heat and dissipate heat, in addition to the reflection principle.

　　Method 5: Use of lamp holder

　　In household LED lamps with low power, the heat-generating drive circuit is partially or completely placed in the internal space of the lamp holder. In this way, the heat can be dissipated by using the lamp holder with a large metal surface, such as the screw-type lamp holder, because the lamp holder is closely connected to the metal electrode of the lamp holder and the power cord. Therefore, part of the heat can be dissipated from it.

　　Method 6: Insulation and heat dissipation plastics instead of aluminum alloy

　　Insulating heat dissipation plastic replaces aluminum alloy to make heat dissipation body. This LED insulating heat dissipation plastic can increase the heat radiation capacity by 4-8 times while maintaining the heat dissipation capacity on par with aluminum alloy. The LED heat dissipation body made of this heat dissipation material can greatly improve the overall heat dissipation effect.

　　Method 7: Integrated thermal conductivity and heat dissipation - Application of high thermal conductivity ceramics

　　The purpose of heat dissipation of the lamp housing is to reduce the working temperature of the LED chip. Since the expansion coefficient of the LED chip is very different from that of the metal thermal conductivity and heat dissipation materials we commonly use, the LED chip cannot be directly welded to avoid high and low temperature thermal stress from damaging the LED chip. The latest high thermal conductivity ceramic material has a thermal conductivity close to that of aluminum, and the expansion coefficient can be adjusted to be synchronized with the LED chip. In this way, heat conduction and heat dissipation can be integrated to reduce the intermediate links of heat conduction.