Thermal simulation to simplify the development of LED light source

Any form of electrical lighting products have a negative product: heat. Incandescent lighting to fluorescent lighting from generation to generation engineers in R & D will minimize heat or heat from the light source separation methods or equipment. However, LED spotlight, currently to continuously improve the quality and increasing form, bringing a new and different challenges.
The development will reduce the heat LED light output, causing the color change, while reducing component life. Said thermal management is by far, the most critical of the LED system design aspects. From an engineer's point of view, this means learning across the structure and tools commonly used in electronic design, electronic design to be familiar with the structure and outside the scope of the process. Fortunately, we already have thermal design solutions, validation and testing in the heat challenges, design engineers can help simplify the road.
Developing a new light system, must verify the most basic product concept, the structural and aesthetic ideas and thermal properties of the actual needs can be unified.
The key success of the LED system design activities, equipment, heat is effectively carried over from its move to the PN environment. PCB and solder the LED housings are involved in the heat flow path. Design engineer must determine the transfer of heat in the shell and shields demonstrated efficiency. Series of physical samples manufactured and tested to verify this is expensive and requires more time, therefore, has the early stages of design engineers in the design of commonly used software-based approach.
More popular approach is to use computational fluid dynamics (CFD = Computational Fluid Dynamics) analysis to simulate the planned virtual devices. For early design concepts, this approach to be flexible than building a lot of physical samples, and just as effective. That the characteristics of a good virtual model, the physical samples can be clear on the basis of what works and what does not. All along, CFD simulation by some of the fluid with a high-level data and analysis of background people to operate, it requires the implementation of personnel in the analysis of complex CFD modeling tools.

The latest CFD technology development will be brought to the structural engineer's desktop, greatly simplifying and speeding up the analysis. The new process, that is synchronized CFD, the preparation and execution of simulation steps to automate most of the work required. Seamless integration with common MCAD in the environment, such as Pro / ENGINEER ®, making the structural engineers can design a new light source to create a virtual simulation model, and detect heat dissipation.
Design verification of the bottom line, whether the product is a new source or modify an existing design, should be a detailed understanding of the thermal performance of LED bulb. If the development of new LED lamps in place of existing equipment, then learn more about the thermal performance is also very important, because the original installation of thermal performance and lighting facilities is the key.
Thermal data from LED suppliers should get the hands, although in the current industry standard in the absence of such information, product specifications in the printing, the information provided is usually not comprehensive enough. For example, the thermal performance data are usually provided, but it may not include the operating temperature range, the actual end-user systems in which the temperature of the work areas. However, design engineers must rely on LED manufacturer's data or simple models to evaluate the implementation of light, or in-house testing, or start early light design.

Six LED application market analysis

Application: the main application market is the LED display, full-color display robust growth.
Early start of China's LED display market, the market appeared a group of highly powerful LED display manufacturer. Currently LED display has been widely applied to the station, bank, securities and hospitals. Demand on the LED, LED display LED indicators in second place behind, the overall LED sales accounted for 23.1%. As for the LED display on the brightness and lifetime requirements higher than the LED lights, LED lights above the average price, which led to the display with LED market reached 3.24 billion yuan, topped the list as more than light The main LED application market. With unique advantages, LED full color display widely used in sports stadiums, municipal square, concerts, stations, airports and other places.
Application 2: small size backlight market slowdown, the large size will become the new focus.
LED has long been used in mobile phone-based small-size LED light backlight market, mobile phone production growth led backlight market's rapid development. In particular, the emergence of color screen mobile phones in 2003 is to promote the rapid development of white LED market. But with the steady growth phase into the production of mobile phones and mobile phone technology to enhance the lead for LED LCD panel backlight to reduce the number, making the LED backlighting in mobile phones in the amount of slowdown in 2005, with LED backlight number over 1.2 billion, the future years, the growth rate will remain in the single digits. The average number of growth slowdown coupled with falling prices, leading to the small size backlight market sluggish, while large-size backlight Although manufacturers market darling, but in 2006 still can not scale. In the above two factors, the backlight market in 2006, a 1% negative growth. 2005 backlight market size of over 1.5 billion.
Application 3: Large market potential for car headlights, but the short term the market is difficult to start.
2005 China Automotive LED application market was 0.29 billion, of which automobile headlights market 0.21 billion. From the LED application market, the automotive market is still in its infancy, the market is small.
LED lights as the car driven by low power consumption, long life and the corresponding speed and quickness. Statistics show that, in the car traveling at 100 kilometers per hour, the vehicle is equipped with LED brake lights are not equipped with LED brake lights than the vehicle braking distance will be reduced by 7 feet. Currently, LED has been gradually applied to the third brake light on the car. Although the LED is still faced with the unit low wattage lumens and related policy constraints, the taillights and headlights into the car market will take some time, but with the decline in the cost-performance ratio and improved luminous efficiency, the LED will gradually realize the ultimate from the vehicle's interior, rear to the front of the transfer, and ultimately occupy the entire automotive lamp market. With the huge capacity car, LED lamp market faces enormous development potential.
Application 4: Interior lighting market has started to enter the market, traffic lights steady growth.
Interior LED lighting market is another emerging market. By current control, LED can achieve hundreds or even thousands of color change. At this stage, the era of personalized attention, LED color LED decorative lights will help diversify the market's development. LED has begun to make small decorative lamps, decorative wall applications in hotels, living room. Interior lighting market in 2005 reached 158 million.
After years of replacement work, the nation's major cities from the traditional traffic lights replaced with LED traffic lights have been drawing to a close. LED traffic lights for many years the market has experienced rapid growth after the 2005 market reached 15.2 billion yuan. But with the completion of the replacement work, LED spotlight lights will no longer maintain market growth is expected to LED traffic lights in 2006 to achieve only 5.8% of market growth to reach 1.61 billion yuan.
Application of five: the rapid development of landscape lighting market, the market growth rate peaked in 2007.
Landscape lighting market, mainly in streets, squares and other public places, decorative lighting, the main driving force mainly from the government. By the 2008 Beijing Olympic Games and 2010 Shanghai World Expo impact of Beijing, Shanghai and other organizations to accelerate the pace of landscape lighting, the LED low power consumption, electricity consumption in the huge landscape lighting market with strong market competitiveness. Currently, LED has been increasingly applied to the landscape lighting market. 2005 Chinese landscape lighting market size of more than $ 700 million in the two main activities, led landscape lighting market will reach 72% in 2007, the high growth rates. In addition, the Olympics and World Expo will be the main role is far longer on their own landscape lighting market to drive growth, more importantly, their role models. In order to meet the Olympic Games and World Expo, Beijing, Qingdao and Shanghai, will build a number of LED landscape lighting, decorative street in these projects will also serve as a model. Other cities see the LED lighting in the landscape will reduce the outstanding performance of the use of LED landscape lighting concerns, accelerate the use of LED landscape lighting applications. LED will fast from one city to the secondary and tertiary urban expansion.
Application of Six: the general lighting market road is long, long way to go.
For into the general lighting market, power white light LED in addition to face, such as low efficiency, poor heat dissipation, high cost and other issues, will face the optical, electronic control and other institutions and the integration of LED lighting products, and develop common standards . Solve these problems requires a long period of time, CCID Consulting forecasts that LED in 2010 can not enter the general lighting market.
As the hotel, Business Center, high-end commercial office buildings and other commercial establishments relative to the price sensitivity is low. At the same time these high-end places more emphasis on highlighting the quality and dignity of the position, for the new products have a greater degree of interest. These are LED lighting to reduce the barriers to entry. LED lighting is expected to be the first to enter the commercial market, and gradually extended to the civilian market.

LED light principle

LEDs are PN junction silicon, electrodes and optical system. From the light - the chip area of 10.2mil (1mil = 0.0254 square millimeters), a large number of current international chip LED spotlight, the chip area of 40mil.
The luminescence process involves three parts: the forward bias carrier injection, recombination radiation and energy transfer. Tiny semiconductor chip is encapsulated in epoxy resin material in a clean, when the electronic through the chip, with the negatively charged electrons to positively charged holes move the domain and with the compound, the disappearance of both electrons and holes generate photons. Between the electron and hole energy (band gap) increases, resulting in the higher energy photons. Photon energy in turn corresponds with the color of light, visible light spectrum, the blue light, violet light energy to carry most, orange light, red light energy to carry the least. Because different materials have different band gap, which can emit different colors of light.

LED street lamp market's future depends on the reliability issue is resolved

Government are currently carrying out most of the world lighting upgrade, the first step is to install LED lights in the new development area, then, LED light will replace the existing old street lighting. According to expect in the next five years, today most of the lights are LED lighting will be replaced.
However, LED lights are facing a big problem is the low reliability because it is mainly used for outdoor lighting, face a variety of extreme environmental conditions, such as long withstand sun and rain, thunder and lightning, temperature changes may be more so. LED lights to be recognized by the market and large-scale use, we must first solve the reliability issues.
TI Semiconductor Division Business Development Manager Liu Chao
TI High Performance Analog Semiconductor Division, Business Development Manager, Dr. Liu Xuechao, said: "LED street lamp market prospect, but must address reliability issues."
LED lights is an optical, thermal and electronics components of complex systems, although a longer LED life of its own, but if poorly designed LED driver circuit, such as the use of low-quality active or passive devices, and the overall life of the drive circuit not match with the LED, LED lights will affect the quality and life.
Furthermore, LED thermal management and heat dissipation is also very important, once the temperature higher than 100 ℃, LED itself, the reliability will be affected. Of course, LED early failure, and transient assembly of local defects and other factors, also led to the LED may fail occasionally, if not take appropriate protective measures diversion, a single LED failure will lead to a whole string of LED does not affect the overall effect of street lighting .
Liu Chao stressed that: "LED lamp is a complex system design, involving light, electricity, heat, mechanical and other fields. Mainly on the drive power in terms of efficiency and reliability problems. First, the driver power supply temperature is high (usually 70 degrees up and down), this way, I hope to drive power efficiency (including the constant voltage with constant current) efficiency reaches a certain height (eg> 90%), reducing the drive power of the temperature, increase reliability, and secondly, the traditional driver topology is more complex, including the PFC, PWM isolation and constant current DC / DC three circuits (see below), components and more, low reliability, especially electrolytic capacitors and opto-sensitive devices. "
Thus, in the process of designing LED bulbs, LED temperature must be well taken into account management or cooling problem, the LED operating temperature remains below its junction temperature (maximum junction temperature of 150 ℃), is generally recommended to be less than the LED operating temperature 100 ℃, avoid affected the reliability of the LED. In addition, LED spotlight circuit designer must carefully choose the circuit in the active or passive devices, to ensure match with LED life. For example, designers should avoid the use of electrolytic capacitors as much as possible, because the capacitor under the conditions in long-term use may cause leakage and result in shortened life expectancy.
Furthermore, LED lighting market in the overall, LED lights are all LED lighting applications the highest power, and therefore require multiple power levels and complex topology to meet the power factor correction (PFC), total harmonic distortion (THD) , 85 PLUS efficiency and other standards and regulations, and multi-string LED current constant demand.
Liu Chao also said: "To solve the problem of circuit reliability of LED lights, drive topology must improve, improve efficiency, reduce component count, while also further reducing costs."