月份：2012年12月

TSMC: the driving voltage of LED drivers can reach up to 60V

TSMC promoted new BCD (Bipolar, CMOS DMOS) module on 15th this month, which can be embedded into integrated LED drivers.

 

TSMC: the driving voltage of LED drivers can reach up to 60V

 

This new BCD technology used in LED drivers can provide a voltage range from 12V to 60V, supporting a variety of LED applications, including backlight of LCD display, LED screens, general lighting applications and vehicle lighting applications. There are several core digital module options, from 0.18 micrometer to 0.6 micrometer. Besides, CyberShuttle also provided TM carpool trial services, which support modules from 0.18 micrometer to 0.25 micrometer.

 

Draw support from multiple integrated features provided by the new technology, system BOM can be reduced. High voltage DMOS not only provides MOSFET switch integration to reduce the number of components, and integrates other electronic components, like high voltage bipolar transistors, high voltage / high precision capacitors, high resistance polysilicon Zener diode (Zenerdiode), etc., but also reduces the number of external component and significantly reduce the area of the circuit board.

 

DMOS supports the advanced drain-to-source-to-resistance (Rdson) effect in IC manufacturing. A specific 60V NLDMOS component, when VB>80V, the Rdson will be 72mohm-mm2, plus the extremely strong current driving capability, engineers can simply increase power efficiency via optimizing the component size. The reliable safe operation area (SOA) can also optimize power switches and driver circuits, making them better. Certainly, there are more detailed characteristics of analysis can also be used as result reference of IC design to achieve optimum chip size and reduce design budget of LED drivers.

 

In the aspect of COMS, 5V voltage is enough to support the Pulse Width Modulation Controller. 2.5V and 1.8V logic cores are common to higher levels of digital integration. In addition, compatible to logic circuits, memory options available for single writing and multiple writing, can also enhance the use of digital programming.

 

According to Mr. Xinsheng Liu, manager of electronic and industrial research and development department of TSMC, in terms of the integration of driver components, the new BCD manufacturing process of LED drivers is a highly sophisticated technology. Related process design kits (PDKs) emphasis on SPICE models with high accuracy, providing more convenient to single-chip design. In addition, MismatchingModEL can help improve the precision in multi-channel LED Tunnel Light driver designs.

The cost of RGB-LED TV technology is expected to drop significantly

“Technically speaking, RGB-LED TV technology is, can be said, perfect. However, the over-expensive production cost is always a big problem that difficult to overcome. After comparing all sort of costs, we decided to put our focus on white LED light sources. ” said Mr. Pyorong, manager of Electronics Digital Imaging Research and Development of Samsung.

 

The cost of RGB-LED TV technology is expected to drop significantly

 

RGB-LED has excellent performances in color gamut but very high production cost relatively. Selling prices of TV sets are hardly accepted by ordinary buyers. White LED light sources are a bit of worse than RGB-LEDs in color presentation, but their relatively high contrast and affordable selling prices (low costs) is incomparable (by RGB-LED TV technology).

 

Since the end of last year, LCD TV sets using white-ray LED backlight technology continued to swarm into the market. According to statistics, Samsung 8000 series all used white-ray side-lighting LED backlight technology. Hisense Blue Media applied white-ray direct-lighting LED backlight technology. Skyworth introduced before the National Day the white-ray direct-lighting super-thin LED TV sets, covering all range from 26 inches to 47 inches. Other manufacturers, including Sony, Sharp, Konka, Changhong, Tongfang all promoted corresponding white-ray LED LCD Televisions.

 

Statistics from DisplaySearch shows that the price of white-ray LED light sources dropped more than 20% every year. Within white-ray LED LCD TVs, the production cost of white-ray LED source occupies more than 1/3, which will inevitably lead to huge price cut and popularization of LED TVs in the future. At present selling prices of TV sets using white-ray LED backlight technology is 1.5 times of ordinary CCFL backlight LCD TV sets. It is expected that this difference will fell to about 1.2 times next year, and achieve a comprehensive replacement to CCFL.

 

Not only application makers are optimistic about the white-ray LED Tunnel Light  sources, even mid-stream packaging companies pay high attention on this part. In the next few years, the cost of white-ray LED backlight technology would certainly be lower than CCFL.

 

In addition, terminal application enterprises increased investment, which helped to keep the cost down. Recently, Tsinghua Tongfang is planning to build the largest LED industry base in China. It is reported that the initial investment of this plan is nearly 10 billion yuan, and the annual output value will reach up to 100 billion yuan.

The high cost of RGB LED backlight technology hard to drop in short term

Earlier of this year, SAMSUNG promoted full-color LED LCD TV sets desperately. Many people felt surprised. Six months later, when the LED TV business rapidly popularized in the global market, competitions can only admired the predict and clever marketing of SAMSUNG. SAMSUNG’s endeavor contributed to the fast popularization of LED LCD TVs in the international market, since a new technological solution has been promoted during this time – white side-lighting LED TV.

 

The high cost of RGB LED backlight technology hard to drop in short term

 

As an upgraded version of CCFL (cold cathode fluorescent tube) backlight, LED backlight technology received high attention from Sony, Sharp and we Samsung since been promoted. In the meanwhile, the large enterprises invested heavily in research and development of technology to reduce costs. When Sony, Sharp concentrated on reducing production costs of RGB LED backlight technology, Samsung shifted their attention to develop white LED light sources, and meanwhile used side-lighting mode to take place of direct-lighting mode. Not perfect, but boosted the popularity of LED Tunnel Light LCD TV technology.

 

The high cost of RGB LED backlight technology hard to drop in short term. Any good technologies want to widely used, production cost reduction is the premise. Currently, LED became the most popular word in the TV market.

 

There are three major LED backlight technologies: direct-lighting RGB-LED source, direct-lighting white LED source, side-lighting white LED source. RGB LED backlight technology is the oldest one.

 

Compared with traditional CCFL backlight technology, RGB-LED TVs have more advanced capabilities in color performance and contrast. As a result of the independent RGB light-emitting components, the color gamut of RGB-LED TV sets can reach more than 120% of the NTSC. Some well-tuned models can even reach up to 150% of the color gamut, completely exceeds the level of plasma TVs.

 

In addition, RGB-LED TV sets can also support technical adjustment and brightness adjustment in the backlight area. Thus in the aspect of contrast, they are able to realize ten million dynamic contrast ratio, which plays a crucial role to enhance the image quality of televisions.

 

RGB LED backlight technology has obvious advantages, making Sony, Sharp and Samsung all spent a lot of money and energy on this part. These three TV giants promoted several related products based on RGB-LED technology, but with ridiculously high selling prices as a result of immature development. From the very beginning to now, after several years of development, RGB-LED did not realize an essential price dropping in production cost. Gradually, these companies reduced investment in the research and development of RGB-LED technology.

White SMD LED investment presents a small climax

After being a distressed industry for a long time, LED lighting has recently become the cash cow again. Xishan Coal and Electricity Power announced their entry to the LED industry, which is very weird, since this enterprise has nothing to do with LED even lighting business. Followed by the Sun Lighting, which has placed a new investment project: “Industrialization project of micro mercury energy-saving lamps”. Sections of this project transformed into “Industrialization project of white SMD LED lighting products with an annual output of 20 million (sets).” Furi Electronics also indicated that the funds will be sought to focus on the development of LED industry.

 

After being a distressed industry for a long time, LED lighting has recently become the cash cow again.

 

The movements of these three companies triggered buzz. The downturn of LED industry has maintained for a very long time. Does this new investment climax in the LED industry mean the new opportunities for LED manufacturers?

 

70% domestic LED companies suggested that in 2012, their sales fell down. A recent report of debt crisis of Horizons Photoelectric caused panic in the LED industry, making the entire white SMD LED industry uptight and sensitive. Early this month, Haobo Photoelectric occurred crisis, causing huge anxieties about whether LED lighting industry will follow steps of PV industry.

 

From the situation of listed companies, in the year to the third quarter, more than 70% LED companies dropped in sales. Potentials exist under the quick success of white SMD LED industry. Overcapacity, vicious competition frequently occurred. Various enterprises produced products with different qualities. It seems that everyone insisted on seizing limited marketing resources even in the condition of long-term loss. LED Tunnel Light industry reshuffle caused by overcapacity is inevitable.

 

Given such distressed background, some enterprises outside the industry tried hard to swarm into it. On 29th of November, Xishan Coal and Electricity collaborated with Guangzhou LEDWAY to established a new companies in Taiyuan – Xishan LEDWAY Co., Ltd. The initial registered capital is 10 million yuan. Products include explosion-proof lighting devices used in mining, white LED sources, road lighting products and other lighting products for commercial purpose. The estimated annual sales is around 30 million yuan. The funder plans to establish the largest high-power LED lighting production base in Shanxi Province in five years.

 

 

How to improve the luminous efficiency of white-ray SMD LEDs

In the past, in order to improve the luminous efficiency of white-ray SMD LEDs, engineers tried to develop large sized LED chips to achieve their goals. However, in fact, if white-ray LED chips continue to work under power supply higher than 1W, their luminous efficiency will reduce by 20%-30% on the contrary. In other words, if white-ray LEDs intend to have brightness several times larger than traditional LED chips and better voltage-current characteristic than fluorescent tubes, they need to overcome following shortages: temperature control, ensure the lifetime of LED chips, improve luminous efficiency and equalize luminescent characteristics.

 

How to improve the luminous efficiency of white-ray SMD LEDs

 

The most effective method to control temperature rising is reducing the thermal resistance of LED chips during the package process. The commonly used method to extend the lifetime of white-ray SMD LEDs is applying small sized LED chips. For the equalization of luminescent characteristics, the most effective way is still optimize the package of white-ray LEDs. More specific methods are still in developing now.

 

The core solution is improving the cooling problem of package. Increasing power will result in drastically reduction of thermal resistance of LED chips to less than 10K/W. In order to solve this problem, many foreign G24 LED makers developed white-ray SMD LEDs with high heat-durability. In fact, high-powered LEDs will generate much more heat (more than 10 times) than low-powered LED chips. High working temperature will speed up the process of light attenuation. But the junction temperature of LED chips can exceed the allowable value and exert very limited influence on the light attenuation. After all, LED engineers started to notice that and spent more energy and money on the package cooling.

 

Using suitable materials can improve the service life of LED chips. For example, siliceous and ceramic packaging materials can increase the service life of LEDs by 10%. The spectrum of white-ray LED chips contains light with wavelength below 450nm, which is also known as short wavelength light. Traditional epoxy encapsulation materials will be easily destroyed by this kind of rays. Plus that the large amount of luminance of high-powered LED chips will also accelerate the deterioration of packaging materials. According to related testing reports, after 10,000-hour constant lighting, the brightness of high-powered white-ray LEDs is reduced by more than 50%, cannot meet the basic requirement of long lifetime of light sources.

Influences of SMD LED beads to LED screens

For full color LED screens, SMD LED beads can be said the most important part. The quality of LED chips plays a key role in determining the quality of LED displays.

 

For full color LED screens, SMD LED beads can be said the most important part. The quality of LED chips plays a key role in determining the quality of LED displays.

 

LED beads are the mostly used components in full color LED screens, there are probably thousands or even tens of thousands of SMD LED beads on every square meter of the lighting board used in LED displays. In addition, SMD LEDs also directly determine the performance, color saturation and sharpness of LED screens.

 

The main performance figure of SMD LED beads mainly determines:

1)       The brightness of LED screens: the brighter the LED chips/the greater the margin of current, the better the quality of LED screens. This type of screens has higher reliability and can save more electricity. LED chips have different angles. With the same brightness, the narrow the angle, the brighter the LED beads, but the visual angle will become narrow all together. Normally, manufacturers choose LED beads with beam angle of 100 degrees to 110 degrees to meet the requirements of visual angle and brightness of LED screens.

 

2)       The failure rate of LED full-color display: G24 LED display is composed by tens/hundreds of thousands of red/green/blue SMD LED beads. The failure rate of LED beads with good quality will be no more than the ten-thousandth after a 72-hour ageing test.

 

3)       The attenuation characteristics of LED full-color display: definitely, the brightness of LED beads will reduce over time, which is also known as light attenuation. The speed of light attenuation is mainly determined by the quality of LED chips, assisted materials and packaging process. Normally, under 20mA driving current, at room temperature, after 1000-hour aging test, the light attenuation of red chips should be less than 7%, and the light attenuation of greed/blue chips should be less than 10%. The attenuation rate of red/green/blue chips has great influence on the white balance of full-color LED screens, and consequently their fidelity.

 

4)       Anti-static ability of LED display: since SMD LED chips are semiconductor devices, they are very sensitive to static electricity, easily leading to static electricity failures. So the anti-static ability is critical to the life of LED displays. Generally speaking, the threshold voltage of body static mode tests of LED beads should not be less than 2000V.

New cooling mode for small and medium power LED lights – vertical heat dissipation mode

Compared with traditional light technologies, LED solid source has high luminous efficiency, pure color, low power consumption, long service life, high reliability, flexible in applications, zero contamination. Currently LED light technology has been widely used in road lighting, residential lighting, vehicle lighting and outdoor landscape lighting areas. Good heat dissipation capability is a basic guarantee for the performance and reliability of LED lamps. Working temperature has significant influences on LEDs’ performances, including changes of color temperature, red shift of wavelength, decline of efficiency, etc. Therefore, good LED lighting devices must be equipped with good heat control systems. In this article, we will discuss about advantages of the vertical heat dissipation mode in small and medium power LED lights. Compared with traditional cooling modes, LED lamps, especially small and medium power LED lights using vertical heat dissipation modes have features of high brightness, fast cooling, low light attenuation, low production cost, reliable. Vertical heat dissipation mode is, can be said, a developing trend of LED lighting industry.

 

New cooling mode for small and medium power LED lights – vertical heat dissipation mode

 

This article will compare new vertical cooling mode with traditional horizontal cooling mode through comparisons between commonly used 3014 LED and 3528 LED respectively. 3528 LED chips realize cooling effects through electrodes weld legs at both ends of electrodes. Thus they use horizontal cooling mode. 3014 G24 LED chips conduct heat through metal substrates, which is vertical cooling method.

 

In order to calculate the thermal resistance more accurately, we firstly set the temperature parameter of substrates as 60℃, chip power as 0.06W, the thickness of solid crystal glue is KER-3200-TI is 0.01mm, the driving current is 20mA. According to the analysis of ANASYS (a type of finite element analysis simulation software), in the same working condition: set as above, the working temperature of vertical cooling mode is higher. This is mainly because that the volume and cooling area of 3014 is much smaller than that of 3528, in which the heat is more concentrated. But the temperature difference of vertical cooling mode is smaller, resistance of which is far lower than LED chips using horizontal cooling method. In other words, the cooling effect of vertical cooling mode is more advance than that of horizontal cooling mode.

 

 

General analysis of traditional LED power supplies

Because of the incomparable features of LED lighting fixtures: environmental friendly, long lifetime, high photoelectric efficiency (the average luminous efficiency of white-ray LEDs has reached up to 100lm/W), LED lighting technology received rapid development in various industries. Theoretically, the average lifetime of LED chips is around 100,000 hours. But this value has never been approved by practical applications. Some LED lamp designers is lack of knowledge of LED power supplies. In order to reduce production cost, they tended to choose cheap LED drivers, without knowing that drivers are one the most important parts of LED lighting devices.

 

Because of the incomparable features of LED lighting fixtures: environmental friendly, long lifetime,

 

LED drivers, also known as LED power supplies, are a type of converter output special voltage and current. The normal input modes of LED drivers include high-voltage low-frequency AC, low-voltage DC, high-voltage DC and low-voltage high-frequency AC (such as electronic transformer) and so on. The output of LED power supplies is normally constant current sources, which can change voltage with the variations of LED internal forward voltage drop. Core components of LED drivers include: switch controllers, inductors, switching components (MOSFET), feedback resistors, input filter components, output filter pieces. According to the requirements of different occasions, output over-voltage protection circuit, input under-voltage protection circuit, G24 LED open-circuit protection, over-current protection circuit are also needed in some cases.

 

Key sections of making a good LED lighting product are cooling sections, drivers and light sources.  The heat dissipation is particular important. And the cooling effect is a direct impact on the quality and the lifetime lighting products. The lifetime of LED drivers, the stability of output current/voltage also have significant impacts on the service life of the entire lamp. Light source is the core part of LED lighting fixtures.

 

Because of the particularity of LED manufacturing technologies, different makers (different products from one makers) will produce LED drivers with huge individual differences in current and voltage. Take 1W high-powered white-ray LED chips for example: generally, the forward working voltage of 1W white-ray LEDs is around 3-3.6V. In another word, suppose the internal current flow of one 1W LED white-ray LED is 350mA, voltage across it may 3.1V, 3.2V or 3.5V. When the internal current flow within LEDs reached 350mA, any tiny fluctuations of input voltage will cause huge increase of forward current, and consequently working temperature, which, as we all know, will speed up the light attenuation of LED chips.

 

How to slow down the light attenuation of LED lamps

Working temperature of LED chips is one of major factors that lead to light attenuation of LED lamps. In accordance with the aging test results of single white-ray LED lamps, if the surrounding working temperature is 30 centigrade, then the bracket temperature of single white-ray LED chip will not be more than 45 centigrade. In this condition, the service life of this single LED chip is “ideal”.

 

Working temperature of LED chips is one of major factors that lead to light attenuation of LED lamps.

 

If there are more than 100 white-ray LED chips work together. The distance between them is supposed 11.4mm. Then the bracket temperature of LED chips on the edge may not surpass 45 centigrade, but the temperature of LED chips in the center will be more than 65 centigrade. Theoretically, in this situation, LEDs in the center will suffer a much fast light attenuation then LEDs on the edge.

 

As we all know, LED cannot stand the heat. The higher the temperature, the shorter the lifetime of LED chips, vise visa. The ideal working temperature of LED chips is from -5 centigrade to 0 centigrade, which is impossible. So that, after learning the ideal operation parameters, designers and engineers need to strengthen the heat dissipation performance of the entire lighting fixture.

 

Another factor that may cause fast light attenuation of LED lamps is the electronic parameter of LED chips. Working under low input current, white-ray LED chips generate low heat, and consequently low brightness. The driving current of LED solar-related LED lamps is around 5-10mA. LED lamps utilized a large number of LED chips, like more than 500 hundreds, may need higher driving current: 10-15mA or more. The driving current of general lighting applications is around 15-18mA. Very few engineers would like to make the driving current more than 20mA.

 

Corresponding experimental data shows that, under 14mA driving current, without any cooling solutions, the internal working temperature is 71 centigrade, the light attenuation of good quality LED chips is almost aero after 1000-hour constant work, and only 3% after 2000-hour constant work. However, this is the worst working condition that good quality (low light attenuation) white-ray LEDs can endured. Working conditions worse than this will cause huge damages to low light attenuation LED chips, speeding up the light attenuation of LED lamps.

Reasons for LED light attenuation

As new lighting source, LED has a lot of incomparable advantages: energy saving, environmental friendly, long service life, etc.. LED-related lighting fixtures received more and more attentions of consumers and producers. But LED light attenuation is also a big problem for LED manufacturers, which must be solved. Fast light attention impact the service life of LED lamps. Now, engineers faced bottlenecks in this area.

 

As new lighting source, LED has a lot of incomparable advantages: energy saving, environmental friendly, long service life, etc..

 

From current situations, LED light attenuation will become the biggest obstacle for LED lighting devices to enter the market of general lighting applications. What causes the light attenuation of LED lamps? Generally speaking, there are two major reasons:

1)       Quality of LED chips: LED chips with bad quality will speed up the lighting attenuation; production process defects, especially defects in the packaging process will reduce the cooling effect of LED chips. Heat generated by LEDs cannot be conducted outward on time, leading to the continuous temperature increasing in LED chips.

2)       Inappropriate applying conditions: normally, LED lamps use constant current power supplies, but some LEDs may be drove by constant voltage power supplies, which will cause long-term damages to G24 LED chips, speeding up the light attenuation; If the diving current exceeds the rated current, there will be more light attenuation, as well.

 

There are a variety of reasons may lead to LED light attenuation, heat dissipation is the most critical problem. Although many LED manufacturers spent a lot of energy and money on the secondary products (LED modules, LED applications), they still cannot maintain normal working conditions for a long time. The light attenuation of these secondary products is more serious than products with good cooling solutions. LED light attenuation has closed relations with the thermal resistance of LED chips, influences from silver plastics, the cooling effect of substrates, colloids and gold wires.

 

The quality of white-ray LED lamps can be said that a rather important factor for light attenuation. For example, same crystal 14mil white-ray LED chip: if using ordinary epoxy as bottom glue, packaging together with white glue and packaging glue, after 1000-hour constant working in 30 centigrade, the light attenuation is about 70%; if using D-type packaging glue, after 1000-hour constant working in 30 centigrade, the light attenuation is around 45%; if using C-type packaging glue, the light attenuation is only 12%; if using B-type packaging glue, the light attenuation is -3% (brighter than original products); if using A-type packaging glue, the light attenuation is -6% (even better).