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LED lighting design of the cooling problem analysis - (AddTime : 2013-03-11)

200W led Flood light as a new generation of lighting received widespread attention. Only by LED packaging and can't make good lighting lamps and lanterns. This article mainly from the electronic circuit, thermal analysis, optical and so on how to use LED the design characteristics of interpretation.

In recent years, as the electronic product high density, high level of integration, the importance of thermal solutions is more and more high, the 200W led Flood light is no exception, also need thermal solutions. Although the incandescent lamp and fluorescent lamp energy loss is big, but most of the energy is through the infrared radiation out, the light source directly produce less heat; And LED, in addition to as visible light energy consumption, other energy is transformed into heat. In addition, due to the LED packaging area is small, through the convection and radiation cooling less, so as to accumulate a large amount of heat.

Thermal solutions is?
Next to consider how to make thermal solutions. Thermal solutions simply say to be solve for heat to produce a variety of problems. Mainly include:

1. Because to thermal expansion bending and crack
2. Electronic circuit operation obstacles
3. Material quality deterioration
In addition, also worried that if fever will not damage to equipment. In order to avoid these problems, to try to control the temperature of the electronic equipment, which means effective cooling is very important, the key is to consider the use of machinery environment and installation method to work out the best thermal solutions. Here's a list of the hot lead to problems. Second half part with LED lights, for example, he LED the relevant solutions for interpretation.

The heat causes problems

1. Because to thermal expansion bending and crack
Electronic equipment by several parts, each of the parts material is different, heat bilges cold shrink scale is different also. Therefore, when all kinds of material combination together of the time it is possible to make the material causes the bending, expands, products in the joint because too much stress can produce crack.

2. Electronic circuit operation obstacles
Generally speaking, as a heat source semiconductor components, a characteristic, and that is when the electronic equipment in the semiconductor temperature rise, electrical impedance will diminish. It'll be easier in "temperature rise - impedance down - current increase - heat increase - temperature rise" vicious circle, and prone to burn out phenomenon.

3. Material quality deterioration
Generally speaking, electronic equipment materials used in easy oxidation, the higher the temperature oxidation faster, if let the material repeated after high temperature oxidation, can shorten its life. At the same time, reheat, material multiple inflation, many shrink, will reduce the strength of the material, and destroy the material.

LED thermal solutions
Below the 200W led Flood light , for example, specific discussion LED thermal solutions.

To avoid the electronic equipment heat has a variety of methods. For instance, add radiator, the heat source for around can provide air conditioning fan. The former is by increasing the cooling area, to increase the cooling channels, the latter is to make hot not heat source gathered round. But, as figure 1 200W led Flood light summary illustration, LED packaging can not be directly connected radiator, also not installed fan position. And internal power supply circuit board will generate heat, so 200W led Flood light heat dissipation problems can be said to be a very difficult problem. So, how to effectively use LED installation materials and radiator is very important.

So how to effectively use the LED installation materials and radiator? You must grasp the produced heat transfer path.

LED the heat generated by the element by encapsulated wire to the circuit board move, and then through the radiator heat release. The heat generated by the power supply circuit board in the same way, through the circuit board ambient air and filling material, through the radiator to the outside heat dissipation.

Thermal solution, it is important to eliminate heat transfer path block heat transfer factors, such as heat transfer path can be used in thermal performance good material, expand the area of path (e.g., thick copper wire than fine copper wire easier to thermal conductivity), besmear thermal lubricant product joint not void.

In addition, even through these improve the thermal properties, but if the radiator to external heat dissipation, internal will gather a lot of heat. Therefore, must improve the radiator surface heat emission characteristics. The typical method is more than the surface installation several fin, enlarge the radiator of heat release area.

Using CAE tools, through the simulation verify thermal solutions

The use of CAE
So how to verify thermal solutions whether effective? One is through the experiment measuring temperature, but when conditions change is to measure, the efficiency is low. Therefore need to use CAE software simulation. Figure 2 by using ANSYS analysis software, the 200W led Flood light transverse put, LED lights around the heat and air flow simulation is the lamp of the temperature profile, red delegation to the high temperature, low temperature on behalf of the blue part. cut piao isonitrile ED packaging surrounding (cover internal) natural convection diagram, red arrow part said convection speed, the blue part said convection slowly. When compared to reality, this case is just a very simple model, but in a way it can verify the product temperature distribution and air natural convection. From the whole lamp temperature distribution to see, although the low temperature, high temperature, but other parts to some extent or in a equal temperature distribution. The surface heat produced by the most are transferred to the radiator, and transfer path no obstacle. Radiator can have a cooling effect, but if the cooling characteristic is not good, the whole lamp temperature will increase, so we must pay attention to the shape of the radiator (install fin size, shape, number, etc.).

According to ANSYS thermal fluid analytical result diagram

Simulation of the shape of the object need analysis, product characteristics, conditions, etc. Various kinds of information, but through the wanted to confirm that information could be the difference between simple analytical model and detailed analytical model, thus effectively grasp want to verify thermal solution is good or bad. For example, in this case is to the electric light simple modeling, and can't grasp the LED packaging internal detailed temperature distribution, but if the parts detailed modeling, can confirm element the actual temperature.

Repeated experiments, through the simulation of modified information can be simple for operation, such as easy to grasp the radiator fin shape and number effect on the temperature. As the simulation software is used, can directly use CAD information to carry on the analysis, can in the unity of tectonic environment, thermal conductivity, thermal fluid and so on a wide range of analysis, and can undertake all kinds of conjoint analysis. In the design should not only consider the problem of heat, and other factors must also be considered, the analysis of the combination of difficulty is skilled carry on the simulation of a key point, these will be discussed in the back.

The only thermal problems were discussed, but there are even solve the hot problem, but can't solve the problem of light, electricity situation. The product is long life, no performance damage, the use of safe, so the task is to realize the overall optimization design.