Development of radiator
As is known to all, LED (Light Emitting Diode) is a solid-state semiconductor device that can directly convert electric energy into light energy. The heart of the LED is a semiconductor chip. One end of the chip is attached to a holder, which is the negative terminal, and the other end is connected to the positive terminal of the power supply. The whole chip is encapsulated in epoxy resin.
A semiconductor chip consists of two parts, a P-type semiconductor, in which holes dominate, and an N-type semiconductor, in which electrons dominate. But when these two semiconductors are connected, a "P-N junction" is formed between them. When an electric current is applied to the chip through a wire, electrons are pushed into the P-region, where they recombine with holes and emit energy in the form of photons, which is how leds glow. And the wavelength of light determines the color of light, which is determined by the material that forms the P-N junction.
When LED converts electrical energy into light energy, the current flows through the LED components, the temperature of PN junction will rise, forming the so-called luminous heat, that is, the higher the current, the higher the temperature, the higher the brightness of the light, many people may say here, since so, why to control the temperature of the LED?
To understand this problem, let's first take a look at how high temperature will affect LED and LED lamps.
Effect of temperature on LED
(1) the LED is mainly composed of stents, silver glue, wafer, gold (copper), which is composed of epoxy resin, which in addition to support and epoxy resin, the other three kinds of material damage can lead to the LED directly to stop working, and high temperature, at the right moment is the bane of the above three kinds of material, under the environment of high temperature LED light failure will increase, reduce the service life of the LED, Some can even burn the gold wire (copper wire) in a flash, leading to direct damage to the LED.
(2) Single LED can not directly meet the use of demand, often accompanied by LED and LED power supply (drive), the power supply itself is a heating body, it has its own temperature resistance requirements, if the temperature is too high, will cause power failure or even damage, resulting in LED lamps can not work normally.
Therefore, it is urgent to solve the temperature problem of LED and LED lamps, that is, heat dissipation.
The cooling principle
Heat dissipation in the traditional sense is the so-called heat transfer, and the principle of heat transfer has the following three points:
1 the conduction
As we all know, heat can be transmitted through the medium, and it can be transferred from the position of the temperature is too high to the position of the temperature is too low. In this case, the conductivity of the material, the thermal resistance caused by the structure of the radiator and the size of the shape may interfere with the heat conduction.
High school physics teacher told us that heat is upward, in fact, this is the so-called radiation, it is very limited with the surrounding environment and the material of the radiation body itself.
Buy a building should be heard a/f this concept, said sales are generally such buildings is very cool, that's true, the so-called convection is cooling through the flow of gas or liquid, it generally depends on the flow of cooling speed, if want to achieve in the lamp body is hard (such as waterproof, safety factor), However, it is not without specific reference to the following graphic products.
The above three points of heat dissipation, now the most used in lamps and lanterns is heat conduction, which is also the topic we focus on today.
Those who read the above text should notice that there are three factors affecting heat conduction: material, structure and size.
In terms of materials, we have to consist of LED lamps. First of all, one of the most common LED lamps is composed of radiator (lamp body), LED, substrate, power drive, optical components. The heating body has LED, drive two, the heat sink has radiator, substrate, or aluminum optical components (heat conduction is almost negligible).
The radiators of LED lamps are generally made of aluminum, which is divided into two categories: AL6060 and other aluminum based tensile aluminum, ADC12 based die-casting aluminum. The thermal conductivity of ADC12 is 96.7w/m deG C, AL6060 and other aluminum is 198~250w/m DEG C, the latter is better than the former in heat conduction, see here some people may ask, since AL6060 and other aluminum heat conduction is so good, why is there ADC12?
ADC12 die-casting aluminum, it to production quickly, can satisfy the general requirements of design aesthetics, is almost you can think of modelling are present), but because change is low, the design of the high cost of the mould, is generally used in size is not very big, don't need to modify the products, the same it is also because the price is relatively cheap, so long on the housing market.
② Tensile aluminum, strong thermal conductivity, low mold cost is generally a tenth of the die casting die, length change is also very flexible, fast processing, mass production, but it can not fully occupy the shell market reasons have the following: lack of hardness, easy to deformation, the appearance of the basic can only be tensile type, less change, can not meet the market appearance requirements.
Based on the above two points, it can be concluded that heat dissipation tensile aluminum is better than die-casting aluminum, and the appearance of the latter is better than the former, which depends on the cost requirements and appearance requirements of the design.
The base plate
In addition to the shell, the substrate is also one of the important heat dissipation body, the market is common can be used for LED lamps on the heat dissipation substrate copper substrate, aluminum substrate, copper thermal conductivity is better than aluminum substrate, but the price is relatively high, most designers or enterprises will choose aluminum substrate as the heat dissipation plate.
① The following figure can be used in the appearance of the fin design.
(2) At the beginning of the design, we should think of the placement of electronic components to avoid the common heat source in the following pictures.
(3) Under the permission of the structure, it is best not to fix the position of the power source to the light source, because in accordance with the principle of heat flow, heat is going up, in the case of no way to control, it is best to reserve the conduction distance to more than 3CM (as for why, please Baidu heat conduction related knowledge). The design plane is shown below.
This will not be detailed, for example, a square meter of material to export 1W of heat, with a square meter of material to export 100W of heat, this concept is very clear, there is no need to elaborate, here can only recommend is to choose a reasonable size within a reasonable range.
Read the above information, a lot of people should understand that thermal conductivity for heat dissipation of lamps and lanterns is crucial, so most people will choose a better heat dissipation material, thereby superstition in the so-called price is high, there is no after validation of high-tech materials, actually has the experiment, using ordinary aluminum radiator, after many tests, The temperature of heat sink is only 3-5 degrees higher than some of the so-called high-tech heat dissipation materials, that is to say, if you can really use a kind of heat conduction material, in the case of zero thermal resistance, can only reduce the temperature 3-5 degrees, but the cost is another talk about it.
In addition to the material, there are also a lot of misunderstandings above the heat pipe, first of all to say what is a heat pipe, heat pipe (heat pipe) is a special material with rapid temperature characteristics, the empty metal tube, so that it has the characteristics of light, and its rapid temperature characteristics, so that it has excellent thermal superconductivity performance; The application range of heat pipe is quite wide, the earliest application in the space field, has been widely used in all kinds of heat exchangers, coolers, natural geothermal reference, etc., as a fast heat conduction role, is now the most common and efficient heat conduction (non-heat dissipation) element in electronic products heat dissipation device.
This section introduces sounds is very tall, but export quantity of heat from the heat sink eventually need by air convection of the tropical, without the cooling fins, heat pipes will soon reach thermal equilibrium, the temperature rise, along with heat sink that is not much meaning, and increase in heat pipe fins, eventually use of cooling fin, Moreover, the contact point of fin and heat pipe is not as good as that of other ways. In addition, it will lead to the increase of cost and the heat dissipation effect is not improved. So in the use of heat pipe, as far as possible to consider the rationality of its structure, can not be used blindly.
Heat dissipation at three points, conduction, convection, radiation, conduction and convection I have explained, and then talk about radiation, in fact, this is not much significance for the heat dissipation of lamps and lanterns, but a lot of people will listen to those manufacturers say what nano radiation materials, in fact, this is really ignored for lamps and lanterns. Why is that? First of all, for lamps and lanterns, the temperature range is about 50-80 degrees, and in this case, even if the radiation material reaches the radiation capacity of blackbody radiation, it can also play a few percent of the heat dissipation, and the coating itself is to hinder thermal conductivity, thus affecting the heat dissipation of lamps and lanterns.