LED has established its unshakable position in the backlighting of portable devices. Even in the backlighting for the large-sized LCD panel, it has started to challenge the mainstream CCFL. In lighting, LED is especially popular in the market due to its highlighted features like energy-efficiency, environmental friendliness, long lifetime, and low maintenance. The driver circuit is a crucial and integral part of the LED. Whether in lighting, backlighting or the display panel, the choice of the technical architecture of the driver circuit must correspond to specific applications.
The LED lighting mechanism goes as follows: when the forward voltage is applied to both ends, the minority carrier and majority carrier in the semiconductor recombine to release surplus energy, giving off photons. The main functions of the LED drive circuit are to transfer the AC voltage into a constant power supply and match the voltage and current according to the requirements of LED devices. Apart from safety need, the LED driver circuit must also include two other basic features:
First, a constant current should be kept as long as it is possible, thus the output current variation is able to be maintained between the range of ±10％ especially when the power supply change goes beyond ±15％range. Here are the reasons for having a constant current driver when using LED as the monitor, other lighting devices or backlighting:
1.To prevent the drive current from exceeding the maximum rate and further affecting its reliability.
2.To meet expected brilliance requirements and ensure the color and brilliance homogeneity of each LED.
Second, the driver circuit should keep low power consumption so that the LED system efficiency can remain at a high level.
PWM (Pulse Width Modification) is a traditional light adjusting technology, which uses simple digital pulses to switch on and off LED driver from time to time. The system only needs to supply wide and narrow digital pulses in order to easily change the output for adjusting LED brilliance. The advantage is that the technology is able to provide high quality white light with high efficiency through easy application. But there is a fatal disadvantage: it is susceptible to EMI (electromagnetic interference), sometimes even produces audible noises.
Voltage boost is an important task of the LED driver circuit, divided into two different topological modes, namely, voltage boost via the inductor and charge bump. As the LED is current-driven, and the inductor is most efficient at the moment of current transfer, so the greatest strength of voltage boost via inductor lies in the high efficiency, which can reach 90% if properly designed. However, its weakness is as much remarkable, i.e., strong EMI, which imposes high requirements on systems of telecommunication products such as mobile phones. With the appearance of charge pumps, most mobiles don’t boost voltage via the inductor. Of course, the efficiency of voltage boost via the charge pump is lower than that in the other way.
No matter in lighting or backlighting applications, the product designer has to face the problem of raising the driver transfer efficiency. To improve the transfer efficiency is not only beneficial for portable products to extend standby time but is also an important means to solve the LED thermal dissipation problem. In lighting, the use of the high power LED also underlines the problem of enhancing the transfer efficiency.
LED needs current and voltage stabilizing components at work, which should be featured with high divided voltage and low power consumption, otherwise, the highly efficient LED will lower the overall system efficiency because of high working consumption, contradicting the principle of energy-saving and high efficiency. Therefore, the main current limiting circuit should use highly efficient circuits like the capacitance, inductor or switching circuit with power supply as it is possible to ensure the high efficiency of the LED system instead of the resistor or the series voltage stabilizing circuit. The series constant power output circuit can keep the LED light output constant in a wide range of power supply, but normal IC circuits will lose some efficiency. The adoption of switching circuit with power supply is able to guarantee constant power output with high transfer efficiency under dramatic voltage variation of the power supply.
At present, LED with its luminous efficacy is far from replacing the three band fluorescent lamps, yet LED lights can efficiently work under safety extra low voltage (SELV), for instances, underwater lights in swimming pools or paddling pools, mining lamps. Besides, LED has unique advantages in the direct use of green energy like solar energy, wind energy, or emergency lights. Particularly in light adjusting, LED cannot only realize zero to one hundred percent adjusting, but also maintain high efficacy during the whole adjusting process without hurting the durability, which is a difficult task for gas discharge lights.
High power LED streetlight is the replacement of the high pressure sodium lamp. Details are as below:
Single phototropism. The feature of LED streetlight pole is single phototropism of light, there is no diffusion of light to ensure light efficiency.
High lighting effect. Twice optical design is unique design of LED streetlight, it remove the light to where needed, improve light efficiency. Currently, LED light efficiency is 100lm/w, and there are much more forward space, say 200lm/w in theory. While luminous efficiency of HPSL is increasing with power consumption, so the total efficiency of LED streetlight is stronger than HPSL’s.
High CRI. The CRI of LED streetlight is much higher than HPSL, CRI of HPSL is around 23, while LED’s is more than 70. From the vision mentality consider, illuminance of LED streetlight lower 20% than HPSL(Take UK Roadway Lighting Standard as reference) .
Lumens depreciation. Decay of LED streetlight is less than 3%, which meet the requirement of roadway lighting standard, while decay of HPSL is more than 30% after one year.
Energy saving. There is automatic control saver, it can meet different illumination requirement for different phase, saving energy hugely.
Safety. LED is low voltage device, safe voltage to drive single LED, single series is 1 watt LED, so it's safer than using high power driver, especially suit for public place.
Easy maintenance. The volume of every LED units, it can form many different shape and be appropriate for changeful environment.
A light-emitting diode (LED)is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor.
An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer life time, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as replacements for aviation lighting, automotive lighting (particularly brake lamps, turn signals and indicators) as well as in traffic signals. The compact size, the possibility of narrow bandwidth, switching speed, and extreme reliability of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are also useful in advanced communications technology. Infrared LEDs are also used in the remote control units of many commercial products including televisions, DVD players, and other domestic appliances.
Officials of the Guangdong Provincial Government stated that they are working towards the goal that by 2015, LED lighting will make up 30% of the interior lighting in Guangdong.
Street lighting is the breaking point for the government to popularize LED lighting: in the next two years, there will be over 600 thousand LED street lamps lightening up the night sky of the Pearl River Delta. The government will implement the LED plan starting in 2012 and aims to increase the penetration rate of LED in interior lighting to 30% by 2015.
At the moment, there are 200 thousand LED street lamps in Guangdong. The Science and Technology Department of Guangdong Province indicated that they will first subsidize enterprises for their LED lighting adoption, and then phase in LED lighting among citizens. In addition, the Science and Technology Department has been considering subsidizing investment institutions and supplying households with free LED lights in order to further popularize LED lighting.
Director of the Office of Guangdong Science and Technology said that the development of LED industry is a revolution
LED lighting industry with high-end new electronic information industry, the electric car industry to work in Guangdong Province is listed as the three strategic focus on the development of new industries, grasp the core technology research, improve the capability of independent innovation, has become the development of LED industry in our province strategic choice and the central task.
March of this year, the Guangdong provincial government executive meeting will be LED lighting industry with high-end new electronic information industry, the electric car industry to work together as a key development in Guangdong Province the three strategic emerging industries, given the historic mission of higher LED industry.How will the layout of the LED industry in Guangdong Development? In the new round of competition in the industry take the initiative? Guangdong how to promote the LED industry? Responsible for leading the LED industry to promote the development of the Guangdong Provincial Science and Technology Department Director Li Xinghua publication of relevant insights.
Made out the core equipment for two years
Li Xinghua Minister said, we selected two breakthrough, the key breakthroughs "core technology and equipment" and "products promote the use of" these two key ports.Epitaxial silicon in the upstream links and key breakthroughs MOCVD (metal organic chemical vapor deposition equipment) and other core equipment and key supporting material, to obtain intellectual property rights, to seize the commanding heights of industry development; downstream market application areas, focusing on expanding the scale LED product applications, driving rapid growth in the consumer market.
At present, epitaxial wafers for LED manufacturing core equipment - MOCVD.MOCVD R & D costs a million dollars, technology and capital threshold is quite high.MOCVD patented technology and market share almost monopolized by foreign companies, equipment in short supply, orders in China for two years after discharged.As the major user of MOCVD, Guangdong LED industry sales and cost under enormous pressure.
After exploring, we have found a way to achieve localization MOCVD.Science and Technology Department of Guangdong Province, Chinese Academy of Sciences Institute of Semiconductors, Industrial Technology Research Institute, Guangdong Province, China Solid State Lighting R & D and Industry Alliance will jointly build a semiconductor lighting industrial Technology Research Institute of Guangdong.We expect within two years, to come up with home-made high-volume MOCVD.
The Government is also about business models
Li Xinghua director said the market was the most critical, how to promote the development of the downstream industry? Downstream aspects of marketing applications, mainly by the Government to start the market.Mainly public lighting, this part of the resources are in the hands of the government, the main choice of high-power street lighting.The promotion of industrial development is vital part of the promotion of large-scale application of this industry to pull up, it will attract more enterprises to Guangdong.So I think that marketing is important, business model is the key.We will now use the EMC model, which is very popular internationally as a model, that is, contract energy management.You do not have money, help you install, from the savings into the electricity, to the deadline to the Government.
"Health Warning" quality control
Li Xinghua Minister said, we have recently found a new way to increase the "supply chain management company," a ring, or "energy management contract (EMC) + supply chain management + financial" innovation business model.Supply chain management company larger than the body, some of its own funds, the banks are willing to give them money, but interest rates still relatively low.Through the supply chain to manage the whole process of the company, to draw into the circle.Now we have the first partner - Guangdong CITIC energy supply chain management company, is the state-owned enterprise subsidiary of CITIC Group.We encourage more involvement of supply chain management company, is now too low. After the launch of this new model, Zhaoqing, Foshan, Dongguan, Zhongshan, Jiangmen City, and Provincial Science and Technology has signed a cooperation to build a "green light model city" of the framework agreement, a large-scale construction of LED street lamp demonstration project. You can control the quality of supply chain management company, how to control it? LED lamp has no national standards, there was a time there was also the view that LED lighting is the "wildfire", it is easy to broken.Would have the advantage of LED lights that save energy and long life, which caused the market to promote a bad influence.
Each cities has its own calculator, use of local products, ah, stimulating local industrial development.This model does not specify our products, but provides good quality products to use.Products into the top ten in the region to give priority to use, can not enter the top ten can not be used.This will ensure the quality of products, but also to break the regional blockade, give full play to the role of the EMC, we did live there.We use the "Health Warning" way, dozens of manufacturers are producing this product, go Health Warning on who wins who will be able to.
We promote the use of LED in the lead in product evaluation benchmark system.LED lights to develop a unified testing methods have been widely acclaimed large-scale applications and a number of enterprise products make regular checks, to obtain on behalf of LED lighting industry, the level of product innovation, dynamic index, which is the benchmark index, the benchmark index, then the quality of products grade, let them go to Health Warning.In the absence of standard cases, this method is very good.
In fact, benchmarking is the standard index of the work of an innovative, we are actively promoting the increased Biaogan system of technical standards for the Union, and through Biaogan system, LED lighting products on the level of technological development and market application status and other indicators of ongoing research, and strive to the formulation of international standards play a leading role. By "Kabo Zi" suffering
Li Xinghua director, said the development of LED industry in Guangdong is facing difficulties and challenges are many.On the one hand, faced with pressure from the developed countries policies.United States, Japan and other developed countries with technical and patent monopoly advantage in the industrial development direction and pace on the way to lead.With the rapid development of LED industry, the competition for the huge market profits, more and more frequently waving the big stick of litigation of intellectual property products, application give the Guangdong-based LED manufacturing industry to bring pressure on the cost, greatly squeezed Guangdong to survive in the international market space.
If not quickly reverse the negative pattern of LED industry in our province could repeat the mistake VCD industry, is to master the core technology of the foreign giants led by the nose by capacity expansion and processing fees to earn a meager price war, sinking low in the industrial chain and recover.
On the other hand, faced with fierce domestic competition.Jiangsu and Zhejiang provinces of China and Shandong and Jiangxi provinces have increased efforts to fight the development of LED industry cake.Preferential measures introduced in some provinces considerable efforts over the Guangdong counterparts.The most obvious example is none other than the shortage of non-MOCVD.
As the international market is highly monopolized the two foreign companies, in addition to expanding domestic production capacity around the race to snatch MOCVD equipment, domestic MOCVD valuable commodity, booked two years after the limited production capacity of enterprises in our province can not meet customer demand, has been a "card neck "of suffering.
Ultimately, the biggest weakness is the LED industry in our province strong capacity for independent innovation in core technology and products do not own intellectual property rights, the lack of "Guangdong-core", resulting in the core competitiveness of industries is weak, unable to grasp the commanding heights of industry and market right to speak. Figuratively speaking, be described as "are bigger, the foundation is shallow."Grasp core technology research, improve independent innovation capacity, the development of LED industry in our province has become the strategic choice and the central task.
Is not the time to talk about excess
Li Xinghua Minister said that the Guangdong are developing around the LED industry, but now is not the time to talk about the surplus, just up until the excess is too early to talk about some signs.Market rule of the market, our market is too great, the TV works, how many water heater manufacturers? LED industry, we are just beginning to talk about excess? We do not do a specific division of labor, to do what the government does not do a up, the place to do it inadvertently, and often this is the case.The process of development restrictions and deliberately do not do too many specifications, we encourage the development of the industry we are very status in the country, this recipe for a use that next year many foreign companies to rush over, and research and development, and production.We use the market to pull up to the industry.