LED is called the fourth generation light source or green light, energy saving, environmental protection, long life, small size and other characteristics, it can be widely applied in various directions, display, decoration, backlight, general lighting and urban areas such as night. In recent years, some of the world's economically developed countries around the development of LED technology in a fierce competition. Wherein the LED heat dissipation has been a serious problem!

There are research data shows that if the LED chip junction temperature of 25 degrees emitting at 100%, then when the junction temperature rises to 60 degrees, the amount of light emission is only 90%; a junction temperature of 100 degrees, drops to 80%; 140 of only 70%. Visible improve heat dissipation, junction temperature control is very important.

In addition to the LED heat will make its spectral shift; color temperature increases; the forward current increases (at constant voltage power supply); reverse current increases; increased thermal stress; phosphor epoxy accelerated aging, etc. problems, so that the heat LED LED lighting design is the most important issue.

LED chip junction temperature is how generated

LED fever because of the added electrical energy into light, and not all, but part of the conversion into heat. LED light efficiency is currently only 100lm / W, its electro-optical conversion efficiency of only About 20 to 30%. That is About 70% of the electrical energy into heat energy.

Specifically, LED junction temperature occurs due to two factors caused.

1. The internal quantum efficiency is not high, that is, when electrons and holes recombine and generate photons are not 100%, commonly referred to as the "current leakage" leaving the area PN carrier recombination rate decreases. Leakage current times voltage is this part of the power is converted into heat, but this part does not account for the main component, because the internal photon efficiency is close to 90%.

2. internally generated photons emitted to the outside of the chip can not be whole and finally converted into heat, which is the main part, because the current is called the external quantum efficiency is only About 30%, most of them converted to heat up.

While incandescent light efficiency is very low, only 15lm / W or so, but it is almost all the electrical energy into light energy and radiate out, because most of the radiant energy is infrared, so the light efficiency is very low, but eliminating the problem of heat dissipation.

Cooling LED is now more and more people pay attention, because the LED light decline, or life is directly related to its junction temperature, heat is not good junction temperature is high, life is short. High-power LED white LED chip cooling applications and solutions

In today's white LED Products are increasingly used in various fields put into use, people feel the amazing power LED white light brings pleasure but also practical issues to worry About its existence!

First, from the very nature of high-power white LED. High-power LED still exists luminous uniformity is poor, life is not long closed material and especially its LED chip cooling problem is difficult to be a good solution, but can not play the advantages of white LED applications are expected.

Second, from the high-power white LED market price is. Today's high-power LED is also an aristocratic white Products, high-power Products because the price is still too high, but also technically needs to be improved, so that high-power white LED Products are not who wants to use it can be used. The following issues related to decomposition of high-power LED cooling.

In recent years the efforts of industry experts, high-power LED chip cooling problems put forward the following points to improve the program:

1. to increase the amount of light emitted by the LED chip to improve the area.

2. Using a small area of the LED chip package number.

3. Change the LED packaging materials and fluorescent material.

It is not by the above three methods can be fully improved heat dissipation problem of high-power white LED Products of it? Actually striking! First we though the LED chip area increases, in order to get by in the more luminous flux (light per unit time the number of beams is the luminous flux per unit area, the unit ml) white hope to achieve the desired effect, but because the actual area is too large, and led to the emergence of some counterproductive phenomenon in the application process and structure.

It is not high-power white LED heat dissipation problem really can not solve it? Of course not impossible to solve. Simply increasing the chip area for the emergence of negative issues, LED white light industry according to the design of the electrode structure improvement and flip chip packaging structure and use of a number of small area LED chips and other ways to improve high-power LED from the wafer surface so as to achieve 60lm / W high low high heat flux luminous efficiency.

In fact, there is a way to effectively improve the high-power LED chip cooling problems. That is its white packaging materials replace conventional plastic or plexiglass with silicone. Replace the packaging materials not only can solve the heat problem LED chip white LED life can be improved even more, really kill two birds with one stone ah. I would say that almost all of the high-power LED white light such as high-power white LED Products are silicone resin as a sealing material should be used. Why are high-power LED silicone must be used as packaging material? Because silica gel for the same wavelengths of light absorption rate of less than 1%. However, the epoxy resin to light absorption rate up to 45% of 400-459nm, easily absorbed due to the long aging of this short wavelength light after leaving the light fades serious.

Of course, there will be a lot of problems such as high-power white LED chip cooling in the actual production and life, because the more people on a wide range of high-power white LED applications will be more in-depth intractable problems! LED chip is characterized in extremely high heat in a very small volume. The LED itself is the heat capacity is small, so must be the fastest speed to the heat conduction out, otherwise you will have a very high junction temperature. In order to maximize the heat to outside the chip, people in the LED chip structure has been a lot of improvements. To improve heat dissipation of the LED chip itself, the most important improvement is the use of better thermal conductivity of the substrate material. Like Cree's LED thermal resistance because the use of silicon carbide as a substrate, the thermal resistance than other companies at least twice as low.

Even if it can resolve from the wafer to the heat resistance between the packaging materials, but the cooling effect from the package to the PCB is not good, is also caused by the temperature rise LED chip, luminous efficiency drop phenomenon occurs. So, like the Panasonic just to solve this problem, starting in 2005, it gave including circular, linear, surface type white LED, and PCB board design into one, to overcome possible because of the emergence from the package to the PCB board between thermal disruptions.

Thus, in the face of the continuous improvement of the current situation at the same time, how to increase heat resistance, but also the stage of the urgent problems to be overcome, in every sense, in addition to the material itself, further comprising between from wafer to packaging materials heat resistance, heat resistance, thermal structure, packaging materials and PCB between the thermal structure of the PCB and heat dissipation structure, all of which needs to be holistic considerations.

LED lighting cooling Questions

The current common incandescent bulbs or fluorescent lamps, even if the product itself is running may produce heat, but the heat component can still be effectively isolated from the light source and power connection seat will not produce heat and unexpected problems. However, solid-state lighting is different, one to focus on running a high temperature LED module single point, must take more active means of heat treatment, and heat treatment with the active and effective mechanism in order to avoid problems with lighting. LED solid-state light source Heat Treatment is much more complex than traditional lighting.

Or more than a traditional light fixtures generate heat during operation problems, such as halogen bulbs or incandescent bulbs, if form incandescent lamp, lamp that is heated in a ball specially treated to produce tungsten light.

In fact, rather than the high temperature generated in the filament lamp holder, lamp holder even due to light ball glass or metal tungsten light of that radiant heat, indirect heat transfer high temperature, but the temperature resulting in acceptable safety range, and then With non-direct Contact conduction, security is relatively high.

But replaced by solid-state LED light source in the form of lamps, the treatment will likely become a New application security issues. Most people would think that LED with high energy conversion efficiency, low driving energy advantages, the use of high security nature, but in fact LED solid-state light source in order to achieve the purpose of the daily lighting applications, it is necessary to strengthen the unit to increase power through a single set of components lumen output member, such as lighting plant will adopt a multi-LED module integration in the form of strengthening the output effect, and multi-component while running can improve LED solid-state light source type deflection point source of the problem, the LED solid-state light source technology lighting produces as bulb-like surface lighting effects. If you want to strengthen the lumen output unit member must be a higher current to the LED chip PN junction produce more lumens, but also makes for higher current single LED assembly point temperature rises, more difficult to handle, even for improve the performance of the optical type, the luminous efficiency of the lamp and take the form of a multi-component and also make the problem of high temperature LED lighting intensifies, so the heat problem more difficult to handle.

Looking at the current development trend of LED lighting market, most of the LED light source manufacturers would most likely be market-driven, because of the high price, high profit to be made by the technical differences quickly into the development of more technologically avant-garde LED light source market, for example, for upholstery, situational lighting applications embedded lamps, wall lamps, ceiling lamps LED light source has become more common form of design, power efficiency to replace the traditional lamp post which is also the most relevant industry attention.

Thermal design LED light fixtures need to focus, where possible in a closed or semi-secret Downlights dead through use, wall lamps, ceiling Products, a more demanding challenge, lamps developers have from the material, product configuration, the main / passive cooling mechanism, the drive chip design and other aspects to invest more resources in order to avoid the Products in question Hajime students. Especially LED Recessed Lighting is small, and often adopt multi-component integration, high thermal design difficulty module. Embedded mining lamp housing or aluminum extrusion heat sink design, can play the role of autologous heat. But this is not enough.

LED thermal management: NTC continuous operating temperature is maintained safe LED lights

If the LED lamp does not come with sufficient thermal management design, during use may cause high fever running lamps because often caused by the sharp drop in life expectancy, resulting in frequent need to replace the failed LED lighting problems, severe Cases may even lead to accidents due to high temperature operation causing lines or the surrounding décor is burning!

In the product development stage, the use of intelligent LED lighting control technology, see temperature performance LED lamps with integral light source module through proactive monitoring, simplify thermal management device, and when the lamp with the ambient temperature rises to zone time, Lamps electric power must be reduced, reducing the LED light output, in order to enhance the use of LED solid-state light source lamp safety.

Like LED Ceiling shell consider a simpler design form, if the lamp itself using a drive that features a more focused on power conversion and LED driver module, not embedded microprocessor temperature control and heat processing module to avoid an increase in raw materials member cost, LED lamps can be integrated NTC (negative temperature Coeffient) NTC Thermistor Sensors electricity, is the relatively high cost-effectiveness of safety design.

The so-called NTC electricity, its purpose is to set back by electronically monitoring the temperature of the LED lamp module, or through the default temperature warning automatic processing corresponding to the driving conditions, picking off the LED solid-state light source module on ways to increase the use of safety LED lamps while NTC electricity also reduces the complexity of the design. Since NTC electric temperature coefficient is very large, so that can detect tiny changes in temperature performance, it is widely used in demand measurement, control and compensation-related electrical design temperatures, whereas NTC electrical LED light source module design, the basic product changes in the surrounding temperature is measured LED solid-state light source lamps, as measured with the voltage situation will change the status of NTC, directly measured the electrical voltage and NTC temperature correspondence.

When the NTC and peripheral level or raise the temperature of the entire module, the electrical resistance of NTC reduced immediately, so the product can be related dependencies security control feedback mechanisms, such as reducing the LED drive current of the light emitting component or directly forced off lighting in fixtures temperature problems improve after automatic reply lighting state, thereby obtaining safety lamp used.

Temperature monitoring LED lamps can import microcontroller mining SMD components manufactured in the form of NTCTHERMISTOR

Improving the aforementioned NTC form of electricity, if you want to achieve better design, with a more sophisticated security MCU design is a relatively pragmatic approach in the development project, the status area may be divided into light LED light source module is normal, lighting is turned off, the temperature warning with temperature measurement program logic to construct a more perfect wisdom lighting management mechanism.

For example, if there is a temperature warning lamp, the temperature measurement module that is still acceptable temperature range can be maintained in the normal way through the natural dissipation of heat sink operating temperature; and when a warning to inform the measured temperature has reached the required implementation of active cooling reference mechanism, this time MCU must control the fan actuator, even when the temperature reaches the value, the system must be directly off the drive power supply through the MCU, LED components temporarily stop running, natural heat dissipation process.

Determine whether to use the lamp on or off using a simple bit of judgment and understanding of the product do change the current status, the more critical part of the temperature measurement, the temperature must be measured in real-time and reference table system for comparison to confirm the current normal or abnormal extent of the module status, calculate the temperature pitch, automatically perform the corresponding temperature management.

Similarly, when the temperature into the zone, the control mechanism should be immediately shut down the light source, while the system is shut down after 60 seconds or 180 seconds after the temperature again to confirm until the LED solid-state light source module temperature reaches normal, then re-driven LED light source, continue to provide lighting. In short:

Volkswagen has been concerned About the life of the lamp. If you rely solely on the use of low thermal resistance of LED components can not build a good cooling system for the light fixtures, and must be effectively reduced from PN node to ambient thermal resistance, can greatly reduce the LED PN junction temperature, and the successful practice of extended LED lamp life and improve the actual flux of the goal. In addition; Different from traditional lamps, the printed circuit board LED power supply both carrier, also LED heat carrier, so the heat sink and the printed circuit board thermal design is very important. In addition, the lighting manufacturer must consider factors quality, thickness and size, and thermal interface thermal processing and material connections.