The hot LED lighting topic has been extended from the beginning of the year to the end of the year. Everyone knows that LED energy saving and long life, but in the face of large-scale applications, but because of power supply mismatch, lack of reliability and other issues have to delay the time to market. More and more people in the industry realize that to fully utilize the potential of LEDs, lighting drive power is one of the key supporting factors.
For LED lighting drive power, the current main demands are focused on high reliability and high efficiency. Xing Xianfeng, general manager of Xi'an Mingtai Semiconductor Technology Co., Ltd. from the local area, clearly put forward three requirements for the current LED lighting driver power supply:
First, it must have high reliability, including long life matched with LED light source, wide working temperature adaptability (-40 degrees - 65 degrees, even -55-85 degrees), and wide grid adaptation and self-protection. Performance, etc.
Second, to be energy efficient, Mingtai Tesemi's product efficiency is as high as 95%, far exceeding the first-class energy efficiency standards of 91% in China and the EU;
Third, in the current LED products without comprehensive standards, LEDs must meet the electrical mandatory standards, especially EMC's GB17743 corresponds to IEC6100, and current harmonic THD's GB17625.1-2003 corresponds to IEC61000-3-2:2001, which requires The power supply must have good EMC, PFC/THD.
iWatt has been working with a number of LED lighting companies to provide power solutions. The company's vice president of sales, Zhu Baozhen, said that the trend of LED lighting power development should be: high efficiency, high reliability, and compatibility with a wide range of applications for dimming and non-dimming. Doug Bailey, vice president of marketing at PowerIntegrations, also believes that all customers need reliable, energy-efficient LED driver products.
Of course, there are other requirements, such as power factor correction (PFC), flicker-free thyristor dimming, high-precision constant-current drive output between different input voltages, temperatures, and bulbs, as well as consistent turn-on and turn-off. Break performance. According to Doug Bailey, PowerIntegrations (PI) devices offer these features in both isolated (LinkSwitch-PH) and non-isolated (LinkSwitch-PL) topologies, depending on the mechanical isolation method chosen and the target application. Security rules.
The current market demand for LED lighting power varies from application to application. The design requirements for consumer light bulbs are quite different from those of street lighting or industrial fluorescent replacement lamps. According to Rohm, the bulb type used for indoor lighting in the LED lighting market has gradually transitioned to a straight tube type, and street lights for outdoor use have also increased. As LEDs have improved in brightness, LED driver circuits have gradually begun to develop toward higher output.
Offline LED lighting power supply into the mainstream
At present, the development of LED replacement bulbs and other new LED lighting is very rapid, and the main market tends to be offline LED lighting power. Peter B. Green, head of the International Rectifier (IR) LED division, pointed out that the offline LED power supply market is mainly divided into high power and low power, which is about 50W, excluding low voltage applications such as handheld devices.
Lamp replacements based on integrated LEDs mostly use a simple, non-isolated buck regulator LED driver circuit. These products use the fewest component count and lowest cost, but must also provide enough lumens per watt, and a power factor higher than 0.7, with standard triac dimmer dimming ability.
Products that do not meet these performance requirements are gradually being replaced, and the US Department of Energy's Energy Star program is one of the reasons for this change.
High power LED drivers typically require insulation isolation to meet UL standards. This often requires a power factor greater than 0.9 and dimming capability, which may be achieved by methods other than the base dimmer. There is also a need to produce at least the same lumens per watt of fluorescent light and a longer lifetime.
Allan Lin, general manager of the Diodes LED lighting business unit, believes that the development of off-line LED lighting power will change the LED sales angle, from low-current, high-brightness LEDs (for mobile phones, logos and laptops) that sell large quantities of DC/DC power supplies, to Higher current LEDs (usually lighting applications) that sell AC/DC power supplies. This will increase the overall general lighting AC/DC LED driver market and increase the need for lower cost power generation.
LED backlighting TVs and other large LCD TV applications are also welcoming other development spaces. They are moving from CCFL to LEDs, further driving the market for higher current LEDs, higher voltage power supplies, and increasing the demand for higher power LEDs that drive many large parallel chains.
Electroless capacitor LED lighting solutions controversy
In most LED applications, the device that has the greatest impact on the life of the LED lamp is the decoupling capacitor. High-temperature and high-reliability capacitors can significantly increase the cost of the BOM, so reducing the size of the capacitor is an important trend and appeal for increasing the life of the lamp and controlling the cost of the BOM. According to AllanLin, Diodes is studying reducing the size of capacitors in future devices.
Not only that, but many manufacturers have introduced LED lighting solutions without electroless capacitors. Creative Electronics Co., Ltd. product engineer Longjin Festival introduced, the company TK5401, IL9910, TK5401 are electroless capacitor drive solutions, mainly used for bulbs, PF value can reach European standard 0.70, few external components, low price, long Life and space saving. With the passage of time, some driving power sources with electrolytic capacitors on the market will have successive failures. Longjin Festival believes that the driving scheme of electroless capacitors is an inevitable development trend.
Although LED is an energy-saving and environmentally friendly product, the current commercial 80-120lm/w light effect is the highest level among all lighting products, but still about 60% of the electric energy cannot be converted into light energy and converted into heat energy. All LED lamps work as a heating body, so that the lamps partially form a high temperature zone of 50-70 degrees or even 85 degrees, and the electrolyte of the electrolytic capacitors will be quickly evaporated and evaporated, and will quickly fail after 1000 to 3000 hours.
Xing Xianfeng pointed out that in fact, the traditional electrolytic lamps and energy-saving lamps drive electrolytic capacitors are also urging the same problem, but the life of the power supply is comparable to the life of the lamp without making the contradiction particularly prominent. He said, "Either reliability or cost, or achievability considerations, electroless capacitors will be the best choice for LED lighting driver power."
There are many other different sounds in the industry for electroless capacitor solutions.
"We don't think that electroless capacitor LED lighting is the development trend of LED lighting power supply. And from the current situation, there are many technical problems to be overcome," Rohm said.
Peter B. Green pointed out that as power requirements increase, the design of LED drivers can become very expensive without the use of electrolytic capacitors. At low power levels, this problem can be solved by replacing electrolytic capacitors with ceramic capacitors, which are difficult to remove on high quality light source fixtures.
In fact, if the electrolytic capacitor is of good quality and can reach an operating temperature of 105 degrees Celsius and a rated working time of 10,000 hours, there is no need to remove the electrolytic capacitor from the LED driver design.
If the temperature of these components can be far more than 10,000 hours under low temperature conditions, for example, at 85 degrees, a component with a rated life of 10,000 hours can run for 40,000 hours.
"The utility is not electrolysis, and its focus is on the life of electrolysis, which is the reliability of the entire product." Zhu Baozhen said that for LED power supply, the most worrying is the natural aging of some components, such as electrolytic capacitors, because its operating temperature is very high. High; secondly, the adaptability and reliability of the drive power to grid fluctuations, such as lightning strikes, because many semiconductor components will fail due to OverStress. Electrolytic capacitors have reliability problems with electrolyte dryness, but simply removing electrolytic capacitors will reduce the power supply's immunity to grid fluctuations and the risk of lightning strikes. Therefore, it is necessary to comprehensively evaluate product reliability. .
The low-frequency flicker caused by the high ripple current caused by electroless capacitors has begun to attract more and more attention. Some researchers believe that strobes below 165 Hz are not easily noticeable by the human eye, but this is already for some people's eyes. Caused by physical discomfort, the large amplitude of the low frequency ripple will also cause some digital camera equipment to appear in the dark and dark grid of the frequency difference. Zhu Baozhen believes that although the market is eager to have a new solution that can solve the capacitor life and maintain stability and reliability, it is difficult to remove electrolytic capacitors on high-quality light source lamps at this stage.
Doug Bailey agrees with this view. He said that for applications that do not require dimming, the use of LinkSwitch-PH eliminates the need for electrolytic capacitors. PI's single-stage PFC/constant current design allows designers to eliminate bulk capacitors, which are typically used between PFC and constant current stages in traditional designs. The only remaining requirement for the capacitor is to power the LED through the low point of the AC waveform (at this point, the voltage is close to zero) in the output.
“This can replace electrolytic capacitors with ceramic capacitors, tantalum capacitors or OSCON capacitors of sufficient capacity to eliminate 100Hz or 120Hz flicker. For high temperature, high reliability industrial applications that are less concerned with dimming, I strongly recommend not using Electrolytic capacitors are designed," Doug Bailey emphasized.
Non-isolated and isolated drive power will coexist for a long time
Currently in the general LED lighting market, there are non-isolated designs and isolated drive power.
Non-isolated designs are limited to dual-insulation products, such as replacements for light bulbs, where the LED and the entire product are integrated and sealed in a non-conductive plastic, so the end user does not have any risk of electric shock. The secondary products are all isolated and relatively expensive, but they are essential where the user can access the LEDs and output wiring (usually in the case of LED lighting and street lighting applications).
An isolated driver or an electrically isolated LED driver means that the LED can be touched directly without touching the battery. The LED driver power supply without the isolation transformer can still achieve partial mechanical insulation by means of the protective casing, but the LED at this time cannot be directly contacted during operation.
Rohm pointed out that how to choose insulated and non-insulated lighting drive power, mainly in terms of safety and size, depends on market needs. "But we believe that insulated bulbs will become mainstream in the future," said the company's responsible person.
Dragon Gold Festival also believes that isolation will become the mainstream of the market. If an isolated drive is used, the secondary side source will not be damaged if there is a problem on the primary side of the power supply, ie the source will not be destroyed. As people pay more and more attention to safety regulations, the market for isolation drive is promising.
Doug Bailey holds different opinions. He believes that the two-stage architecture is suitable for older drives that must use a second constant current drive circuit to enable the PFC to drive the LEDs at constant current.
These designs are outdated and no longer cost effective, so in most cases it is best to use a single stage design.
The physical design determines whether the drive is isolated or non-isolated. Security rules usually require the use of two separate isolation layers. Designers can choose between two physical barriers, a plastic diffuser and a glass shield, and use a non-isolated power supply. If physical isolation costs are too high, there are mechanical difficulties, or too much light is absorbed, electrical isolation issues must be addressed in the power supply.
Doug Bailey pointed out that isolated power supplies are typically larger than non-isolated power supplies of the same power level. Lighting designers must perform significant cost and design optimizations in each of the products they design.
Xing Xianfeng also said that the simpler the solution, the more advantageous it is, so the single-level framework has always been the direction that designers are pursuing.
“There are a lot of ways to implement 'offline' LED power, and the best way depends on the final application,†AllanLin said. “We foresee that single-stage (no isolation and isolation) will dominate the replacement bulb (E27, GU10). , T8 type lights), for these products, the cost and size of the solution is crucial."
Since it is suitable for different applications, whether it is an isolated insulating transformer or an isolated protective lamp housing, the designer will always have different opinions in different angles. Often, they analyze in many ways, such as cost and manufacturing processes, efficiency and volume, insulation reliability and safety specifications, and so on.
Supertex believes that both architectures will become popular in the future. Peter B. Green also said that in the future these two types of design will continue to be used, because each design meets different market needs.
Drives with transformers cost more, but they also make LED luminaires more practical and meet the needs of end users who accidentally touch LEDs. When the incandescent glass casing is easily damaged, an ordinary bulb of the E27 model can be replaced with an LED lamp. In addition, luminaires in industrial areas or office equipment applications do not need to reach end users, such as street lights and mall lighting, where LED lights do require isolation transformers.
Zhu Baozhen said that as a product that can be safely used by end users, the reliability of insulation and isolation must be considered. As a complete product, the parts of the product surface that are accessible to the user must be isolated and not subject to electric shock. From the perspective of the entire system, isolation is inevitable, the only difference is the location of the isolation. Some designers use isolated transformer designs so they can simplify heat dissipation and lampshade design. If a non-isolated drive design is used, reliable insulation requirements must be considered for structures such as lamp housings. Therefore, as a power driver, both isolated and non-isolated solutions exist simultaneously.
iWatt's iW3610iW3612 series ICs have integrated traditional two-stage control (PFC+PWM) into a SO8 package that provides both constant current control and phase-cut dimmers, as well as improved power. factor. Zhu Baozhen said that this design meets the mainstream requirements of the LED market.
Local manufacturers face cost pressures
Today, a large number of small companies have entered the LED lighting business, and the market price has been declining due to competition. How to ensure the reliability and quality of design under fierce competition, not just providing the lowest cost solution, has become a challenge for many local OEMs.
“The challenge for everyone in the LED industry chain is to reduce the overall cost of the lamp every month.†Allan Lin, general manager of the Diodes LED lighting business unit, said the low-cost BOM solution also has strict LED power factor and efficiency specifications. .
The main challenge that Chinese LED driver manufacturers may face is finding low-cost AC/DC drivers to achieve tighter power factor and efficiency performance in low-cost power systems.
In the future, the use of high-quality, high-reliability power supplies in systems where space is limited and where heat dissipation is difficult (such as LED luminaires) will no longer be free. However, it is quite difficult to prove that its quality is high before the end user has used many of the bulbs that last for about 10,000 hours.
Doug Bailey, vice president of marketing at PowerIntegrations, said that things would be much simpler if they were driven by a drive controller company that produces high-quality power products for harsh environments such as home appliances and electricity meters.
LED is a brand new lighting system, LED driver needs to work with LED and its module coordination system. "LED driver is not a simple power supply problem. It must not only meet the LEDPN junction load requirements, but also consider the LED module optical and electrical structure design." Xing Xianfeng pointed out that "the current LED driver manufacturers are almost all traditional power supply manufacturers. Lack of system solutions and comprehensive considerations."
Peter B. Green from IR pointed out the problem of product quality standards. In order to sell LED drivers in the US and Europe, Chinese OEMs must create well-designed, high-reliability products that fully meet UL and ENERGY STAR requirements. The life of the product is critical, so the use of high quality components and production quality control is critical. At the same time, the cost must be reduced as much as possible while ensuring high performance and reliability.
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