New product analysis report of 19 LED driver ICs in 2009 (1)

Abstract: The development of semiconductor lighting technology and industry is much faster than people expected. Some characteristics of LED light source are unmatched by any artificial light source, such as rich color, high color saturation, concentrated beam, solid-state illumination, fast response. , brightness and color can be digital, intelligent, networked control and adjustment, and so on.

Foreword

The development of semiconductor lighting technology and industry is much faster than people expected. Some characteristics of LED light source are unmatched by any artificial light source, such as rich color, high color saturation, concentrated beam, solid state light, fast response, and brightness. And color can be digital, intelligent, networked control and adjustment, and so on. The wide application of these new features will change the experience and habits of people's traditional lighting, trigger the transformation of lighting concepts and light culture, and promote the development of lighting products in a people-oriented and more humane direction.

The most important point is that LED lighting meets the trend of energy conservation and environmental protection. For this reason, governments have introduced policies to promote the development of solid-state lighting technology. The US Department of Energy has been promoting research and development of solid-state lighting technology as early as 2000, and has supported many R&D projects. achievement. It can be said that the implementation of the SSL plan has made considerable progress in the field of solid-state lighting. The Ministry of Science and Technology of China has launched the "Ten Cities and Ten Thousand Miles" semiconductor lighting demonstration project to push LEDs to a broader market and promote the LED industry to become bigger and stronger. At the same time, the European Union, Germany, Japan, South Korea and other places have also launched similar plans. The successive introduction of these policies will accelerate the development of LED lighting.

Since the LED is a characteristic sensitive semiconductor device, it has a negative temperature characteristic. Therefore, it is necessary to protect the stable working state during the application process, thereby generating the concept of driving. Unlike ordinary incandescent bulbs, LEDs can be directly connected to 220V AC mains. The LED is a low voltage drive of 2 to 3 volts, and it is necessary to design a complicated conversion circuit, and the LED drive power supply is highly required. The quality of the drive power is one of the key guarantees for the longevity of LEDs.

This report mainly analyzes the market shape of LED driver in 2009, the technical difficulty of LED driver, and lists the new LED driver IC products newly launched by 19 excellent LED driver IC manufacturers in 2009, hoping to provide some options for the selection of LED driver ICs. help.

Chapter 1 Status of LED Driver Market Industry at Home and Abroad

1.1 LED Driver International Market Analysis

LED driver market distribution (Research and Markets research institutes perspective (2009-07-02))
Since the commercialization of high-brightness LEDs (100 lm/W) and the continuous price reduction of LEDs (1 yen/lm), LEDs have become easier to enter into diversified applications, and LED-related terminal products have developed more rapidly. Among them, the main hero of LED lighting is the LED driver IC. Figure 1 below shows the global LED driver IC market value forecast.

Figure 1 Global LED driver IC market value forecast Source :IMS

At present, the application goals of LED are very wide: mobile phones, handheld devices, LCD panel backlights, car headlights or other sources of light applied to outdoor, office and home. In the short term, the main application of LED will be extended from mobile phones to LCD panel backlights. Research and Markets research institutes have found that although the main market for LED and LED driver ICs is now in mobile phones, since 2010, LED and LED driver ICs for LCD panels or LCD TVs will become their biggest mainstream.

Research and Markets believes that LCD TVs grew at an annual rate of 95% in 2006 and became a 57% growth rate in 2007. To put it simply, once the growth trend slows down, the competition among manufacturers will begin to change. Under such influence, LCD TV manufacturers can only obtain better profits by strengthening product differentiation, so LEDs are adopted. As a backlight, it has become one of the key points.

According to estimates, the average growth rate of LCD TV shipments from now to 2011 will be more than 25%, and in 2011, it will reach 200 million levels, which is a very large market for LED driver ICs. .

In addition, the growth of LED backlights in notebook computers will also grow by two digits in the coming years. Research and Markets estimates that the growth rate of notebook computers in 2008 will reach 25%, and in 2009, notebook computer shipments will surpass desktop computers for the first time. Therefore, in the next few years, notebook computers will also be the driving force for the growth of LED and LED driver ICs.

In terms of automotive LEDs, the use of automotive LEDs and LED driver ICs will continue to increase due to continuous breakthroughs in heat dissipation technology and continued reduction in cost of major components. Future LED headlights will also extend from premium cars to general caravans. LEDs are used in general lighting because the current needs to be controlled with a constant current. Therefore, LED lighting manufacturers tend to customize the LED driver IC design to meet their needs.

1.2 LED drive domestic market analysis

Current status of domestic and foreign markets: iSuppli's point of view (2009-07-31)

At a time when the global economy and electronics industry are sinking into recession, China's LED driver IC market will only grow by 1% in 2009, from $115.3 million in 2008 to $116.5 million. However, the growth rate in 2010 will accelerate to 9.6%, and the scale will reach 127.7 million US dollars. The LED market in China is expected to reach $139 million in 2013.

Figure 2 shows iSuppli's forecast for China's LED driver IC market.

The Chinese government has taken measures to stimulate domestic demand and encourage companies to invest in the LED industry, which is driving domestic LED driver sales growth.

Foreign companies currently control China's LED driver IC market, especially US companies such as Texas Instruments, National Semiconductor and Linear Technology. These suppliers are geared to different markets, each with its own special requirements, including mobile phones, portable consumer electronics, automobiles, signage/large displays, traffic lights and general lighting. In addition, Taiwan LED manufacturers are also active.

Before 2008, there were only a few local semiconductor manufacturers in China focused on the LED driver market. However, since last year, as China has taken measures to develop domestic supply to meet the needs of LED urban lighting and other projects, more and more domestic companies have begun to enter the LED driver market. However, most of these new manufacturers joining the LED driver market are non-factory companies. Since 2008, more than 40 fabless IC design companies are developing LED driver ICs. iSuppli believes that almost all vendors focused on the power management IC market will launch their own LED driver IC products in the next two years.

iSuppli predicts that Chinese companies will make great progress in this market. They strive to achieve rapid growth over the next five years, especially in the backlighting of mobile phones and consumer portable devices.

Chapter 2 LED Driver Basics

2.1 Introduction to LED Driver Topology

LEDs can be divided into three categories according to the application: illumination, backlight and display. Most LED driver circuits fall into the following topological types: buck, boost, buck-boost, SEPIC, and flyback. In order to achieve more efficient LED lighting, a new topology is needed to provide a solution, from a flyback topology to a resonant half-bridge topology, to take full advantage of the zero voltage switching topology (ZVS). In addition to this, there are simple current limiting resistors or linear regulators to drive the LEDs, but such methods typically waste too much power. The main design challenges for LED lighting applications include the following: heat dissipation, high efficiency, low cost, dimming without flicker, wide dimming, reliability, safety, and elimination of color cast. These challenges need to be addressed by a combination of appropriate power system topology, drive circuit topology, and mechanical design.

Table 1 LED drive common topology diagram

Regardless of the output power of the LED lighting system, the choice of LED driver circuitry will depend to a large extent on the input voltage range, the cumulative voltage drop of the LED string itself, and the current required to drive the LED. This has led to a number of different possible LED driver topologies such as buck, boost, buck-boost and SEPIC, flyback topologies, and resonant half-bridge topologies. Each topology has its advantages and disadvantages.

Design parameters related to the LED driver circuit include input voltage range, number of LEDs driven, LED current, isolation, EMI suppression, and efficiency. In general, LED lighting design needs to consider the following factors:

Output power: related to LED forward voltage range, current and LED arrangement, etc.

Power supply: AC-DC power supply, DC-DC power supply, direct AC drive

Functional requirements: dimming requirements, dimming methods (analog, digital or multi-level), lighting control

Other requirements: energy efficiency, power factor, size, cost, fault handling (protection characteristics), standards to be followed, reliability, etc.

More considerations: mechanical connection, installation, repair/replacement, life cycle, logistics, etc.

2.2 LED lighting driver

LED lighting meets the trend of energy saving and environmental protection. The prospects are clear. Although the backlight and display technologies have been developed for many years, the solution is relatively mature, but it is not as bright as the market, and it is competitive in many related consumer electronics markets (such as mobile phone backlights). The cost is high, the price war is frequent, and the profit margin is greatly limited. Some people think that perhaps in 2-3 years, LED lighting technology will have a breakthrough, and the market will start on a large scale. At the same time, the application of LED lighting continues to expand, and new markets are constantly emerging. Perhaps the market for high-power street lights and general lighting is slow to start, but you will find that some low-power lighting markets are developing rapidly, such as decorative lighting, portable product lighting and so on.

US Department of Energy (DOE) Energy Star (ENERGYSTAR) Solid State Lighting (SSL) Specification:

Power Factor Correction (PFC) is mandatory for any power class specified by the US Department of Energy (DOE) ENERGY STAR Solid State Lighting (SSL) specification. This standard applies to a range of specific products, such as recessed lights, cabinet lights and table lamps, where the LED driver power factor for residential applications must be greater than 0.7, and for commercial applications greater than 0.9; however, this standard is a voluntary standard. The European Union's IEC61000-3-2 Harmonic Content Standard specifies the total harmonic distortion performance of lighting applications with power greater than 25 W, with a maximum limit equivalent to total harmonic distortion (THD) of 0.94.

While not all countries absolutely mandate improved power factor in lighting applications, some applications may have this requirement, such as utilities that promote commercial applications of products with high power factor in utilities, and utilities. When an organization purchases/maintains a street light, it can also decide whether it is required to have a high power factor (usually 0.95+) according to their wishes.

The US Department of Energy's ENERGY STAR recently released its proposed integrated LED lamp (which is typically screwed into an ANSI standardized lampholder, similar to most incandescent lamps on the market today). Draft revision 3 of the proposed standard specifies power for ≤ 5W. The lamp does not require a minimum power factor. For a 5W lamp, the power factor must be ≥ 0.70.

LED lighting system topology selection:

The choice of LED lighting system architecture depends on whether your design goal is low cost, high efficiency or minimum PCB area. In general, LED lighting systems smaller than 25W do not require power correction, so simple topology such as PSR or Buck topology can be used. 25W-100W LED lighting applications require power calibration, so single-stage PFC, quasi-resonant (QR) PWM or flyback topologies are typically used. LED lighting applications above 100W generally use more efficient LLC topology and PFC. From an efficiency point of view, LLC and QR perform better; the PSR scheme does not require secondary feedback, is simple in design, and is smaller in size than other solutions. ”

In terms of DC-DC solutions, the standard buck converter is the simplest and easiest to implement, followed by boost and buck-boost converters, while SEPIC converters are the hardest. This is achieved because it uses complex magnetic design principles and requires designers to have superior switch mode power supply design expertise. The application of the terminal product determines the topology of the LED, and then the Buck, Boost, SEPIC (less used), or Buck-Boost structure is reasonably selected according to the topology of the LED and the input power. "In general, there are more Bucks below 25W. The larger powers tend to choose the Boost structure. If the efficiency is both, the two can generally achieve more than 85%. The low-power LED lights should adopt a highly integrated solution. High-power solutions should use products with high technology integration.

2.3 LED backlight driver

The application of LED backlights on small-sized screens such as mobile phones, digital cameras, and PowerDVDs is very mature, and there will be no high compound annual growth rate in recent years. With the improvement of LED luminous flux, cost reduction, green environmental protection of LED (CCFL backlight containing mercury), wide color gamut, local dimming, etc., it meets the current development requirements of LCDTV HD energy saving. Therefore, the growth point of the backlight will be applied to large-size screens in notebooks, LCD TVs, and the like.

Mobile handheld and other display products backlight LED driver IC selection, according to the area of ​​the LCD to set the number of LED point light source; according to the LED N string N and the lighting mode to select different working principle, LED output with different output capabilities IC; 1.8-inch to 3.5-inch mobile phone with LCM LED point light source is 2 ~ 4 LED; 3.5-inch to 8.0-inch MP3, MP4, PDP, GPS, PND, DPF with LCM LED point light source is 6 ~ 28 LED; 12.1 inch to 15.4 inch notebook LCM LED point light source is 48 ~ 60, 60 ~ 72 LED; mobile phone has RF fear of interference, so most do not use the inductor as the electrical storage DC / DCBoost; DC/DCBoost is mostly used in consumer electronics without RF because it can output higher voltage and higher efficiency. Commonly used LED driver ICs are charge pump (Charge Pump), constant current source (Constant current), and inductive step-up switching regulator (DC/DC Boost). Below is a selection table for the backlight driver IC for mobile handheld display products.

Table 2: Choice of backlight driver IC for mobile handheld display products

2.4 LED display driver

As a high-tech product, LED display has attracted people's attention. The intelligent full-color display that integrates light and electricity with computer control has been applied in a wide range of fields. The pixel points adopt LED light-emitting diodes, and many light-emitting diodes are arranged in a dot matrix to form an LED array, thereby forming an LED screen. Different effect images can be obtained by different LED driving methods. Therefore, the advantages and disadvantages of the LED driver chip play an important role in the display quality of the LED display. LED driver chips can be divided into general-purpose chips and dedicated chips. General-purpose chips are generally used for low-end products of LED displays, such as single and dual-color screens in indoors.

Figure 4 The basic structure of the LED display system

At present, LED driver-specific driver chip manufacturers mainly include TOSHIBA (Toshiba), TI (Texas Instruments, USA), SONY (Sony), MBI (Accumulation Technology), SITI (Site Technology). In the domestic LED display industry, these chips have applications.

Since the LED is a current characteristic device, that is, under the premise of saturation conduction, its brightness changes with the magnitude of the current, and does not change with the voltage across it. The biggest feature of the dedicated chip is to provide constant current source output, to ensure stable driving of the LED, and to eliminate the flicker phenomenon of the LED. It has the characteristics of large output current and constant current, and is suitable for occasions requiring high current and high image quality, such as outdoor full color screen and indoor full color screen.

The LED display driver is generally a multi-channel constant current source (currently 16 channels) plus grayscale control. The IC does not integrate DC/DC power modules. In backlights and illumination drivers, the number of channels will be Less, and the DC/DC converter module is usually part of the IC. The LED display pays great attention to the refresh rate and image performance of the screen. High matching, high refresh rate and high resolution are important indicators for judging the performance of an LED display. This requires high consistency of current between the LED display driver IC channels, high-speed communication interface rate, and constant current response speed. The display-driven technology focuses on LED grayscale linearity and fast output response. The backlight factory uses multiple and multi-string architectures to achieve operating voltages as high as 50V to 60V, which will increase the process technology required for the driver IC. The VF difference of each LED after string high voltage needs to be considered. This has a large impact on overall power efficiency and constant current control. The following table shows the key indicators of the LED display screen drive.

Table 3 LED display screen drive key indicators

2.5 LED car lighting driver

For automotive applications, LEDs are extremely attractive, and their longevity, shock resistance, high efficiency, and good control of the light source are all advantages. Of course, compared to incandescent lamps, LEDs need drive circuits, and automotive electronics are powered by acid-lead batteries. They are mechanically driven alternators. These batteries are suitable for incandescent lamps and are not suitable for LEDs. Therefore, design is stable. A drive circuit with good voltage performance and low noise is very necessary. The range of automotive power supply varies widely, from 8V to 18V, with peak voltages of up to tens of volts. In addition, the high-brightness LED drive current is large, which generates a large amount of heat in the resistor, complicating the heat dissipation design.

Figure 5 shows various LED lighting applications in modern cars. Inside the car, there are several "standard built-in" lighting modules that use various types of LEDs. Some are single LEDs, while others such as navigation dashboard backlighting require LED arrays. LEDs are also recognized for external lighting. More than 40% of the central high-position brake lights now use red LEDs. In addition, the Audi 2008 A8 uses a high current LED array as the daytime running light (DRL). All external "forward illumination" of the Lexus 600 sedan and the Audi R8, including the headlights, are done by LEDs. Similarly, even more mid-range cars and many motorcycles use color LED arrays as brake/turn signal indicators.

Figure 5 Typical application of LED lighting in modern cars

The following picture shows the structure of the car lighting drive system

Figure 6 Automotive lighting drive system structure

The following table shows the common topology table for automotive lighting drivers.

Table 4 Common Topology Table of Automotive Lighting Drivers

2.6 Dimming Technology - Analog, PWM, and TRIAC Dimming

LED dimming solutions and specifications have been constantly changing, and have not been fixed until now, so there are three dimming schemes for PWM, analog and thyristor (TRAIC) on the market.

The PWM and analog methods are simpler, but require a dimming infrastructure and a new dimming controller. A disadvantage of the analog dimming scheme is that the adjustment range of the LED current is limited to a certain maximum to about 10% of the maximum (10:1 dimming range). Since the chromatogram of an LED is related to current, this method is not suitable for some applications. The PWM dimming scheme switches between zero current and maximum LED current at a rate that is fast enough to mask visual flicker (typically above 100 MHz). This duty cycle changes the effective average current so that a dimming range of up to 3000:1 can be achieved (limited only by the minimum duty cycle). Since the LED current is either at its maximum or turned off, the method also has the advantage of avoiding LED color shift when the current changes, which is common in analog dimming.

Regarding TRIAC, there are different opinions:

TRIAC dimming is a hot topic in the industry. Initially, TRIAC dimmers were designed for incandescent lamps, but most users expect the same TRIAC dimmers to dim alternative LEDs.

Opinion 1: Sang Cheol Her, senior manager of high-voltage IC products at Fairchild Semiconductor, said that he is optimistic about the market prospects of TRIAC dimming solutions. SCR (TRIAC, 2-wire dimming) will become a very popular solution because it can be fully used. The traditional system does not require any changes. Moreover, it can be extended to 3-wire dimming to avoid defects associated with low power factor values. ”

Viewpoint 2: Xu Ruibao, engineer of Cytech's product and design department, believes that the choice of modulation method should not be determined by the power of the LED. It should be determined by the application requirements of the terminal product. For example, the display backlight or LED decorative light may use PWM dimming mode, with good color consistency and high brightness level. However, for general household lighting or commercial lighting, analog dimming or TRIAC can also be chosen, but color shift will occur and the level of dimming will be low. Tony Armstrong also pointed out that the dimming method used by end users will largely be determined by the end use of the LED itself. For example, in automotive infotainment systems where LEDs are used to provide backlighting to displays, the brightness of ambient lighting The range of variation is very wide, from the incomparably bright when there is plenty of sunshine, to the darkness of the moonless night, which is very different. Because the human eye is extremely sensitive to slight changes in ambient lighting conditions, it requires a wide dimming of 3000:1. Scope. This will require the LED driver circuit to use PWM dimming. However, he added: "In LED street lights, because this lamp is often either on or off, only a limited dimming is required. The scope is fine. In this case, only a simple analog dimming method can be used to meet the requirements. ”

Viewpoint 3: Zheng Zongqian, senior application manager of ON Semiconductor China, believes that the application of TRIAC dimmers on the market should be only transitional. In the long run, PWM dimming should be used. The main three decisive factors are: 1) PWM dimming from zero to the most light, there will be no flicker. 2) Performance will be better. Because the dimming output power uses a power factor correction circuit, which is in line with the global requirements for the power factor of the light, although generally starting from 25 W, the United States requires that the light must be forced from zero watts. Factor correction circuit. The use of TRAIC dimming will sacrifice power factor and increase circuit complexity. Therefore, the use of PWM dimming can provide the best performance choice and is the future trend. 3) The cost will be better. Adjusting the duty cycle with PWM does not require much additional control circuit cost. Alexander Sommer, Director of Product Marketing, Power Management Business Unit, Infineon Technologies, Inc., also said that he is optimistic about the prospects of PWM dimming solutions. He said: "Compared with analog dimming methods, LED PWM dimming methods have the following advantages: 1) Efficiency Higher; 2) Regardless of the degree of dimming, the LED is allowed to operate under optimized and constant current; 3) The color tone of the LED remains the same throughout the dimming range (color tone is the same as LED output current as lumen output) And change). ”

In order to achieve flicker free during continuous dimming, most customers prefer PWM dimming because it provides a larger dimming range and better linearity. Depending on the dimming frequency you are using, flicker can be minimized. Analog dimming is easier to implement because it requires only one DC voltage to dim the LEDs without flicker. For high-power lighting applications consisting of multiple LEDs, ensuring uniform brightness per LED and not producing any flicker has become a major design challenge, but the PWM method easily resolves flicker problems during dimming.

As mentioned earlier, LED lighting applications of less than 25W are primarily replacing standard incandescent and halogen lamps. The most likely application in this power range is to replace incandescent or energy-saving lamps controlled by TRIAC (two-way thyristor)-based step-down in-wall dimmers. There are cutting-edge and trailing edge dimmers on the market today, which poses a challenge for overall compatibility because TRIAC dimming is poor from an EMI perspective.

“For non-dimming applications that require the best price/performance ratio, a single-stage PFC flyback topology using a DCM PFC like the Infineon NCP6561 is a suitable choice.” Alexander, Product Marketing Director, Power Management Business Unit, Infineon Technologies, Inc. Sommer believes that "25W and above power range LED lighting applications are targeted at more specialized markets. The choice of dimming control method will depend on whether it is an alternative or a new installation. Digital lighting control (such as DALI or wireless solutions) allows Dimming levels for more precise control and more features such as daylight dimming and duty cycle sensing. Alternative installations may require compatibility with older analog 1-10V dimming controllers.
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