I recently interviewed an associate professor of Guangxi University, Wang Xi-day, he specializes in power supply design, LED power supply in recent years actively engaged in the design of which, especially in the field of electrolytic capacitors in the absence of depth. Led lighting industry for the current difficulties and countermeasures, Wang Xi-day has its own unique insights.
LED light bulbs Energy Star specification for the healthy development of industry
Industry spread saying: "first-class standard-setting profits, profit second-rate competition in the patent, third-profit brand strategy, the four current profit is the price war." November 2009 announcement of the "Energy Star LED bulb Specifications" landmark. Although only bought in the U.S. market posted the "Energy Star Certified" logo LED light bulbs, only to enjoy the U.S. government financial subsidies to buyers, but this is the world's attention to LED lighting industry can not regulate the first LED light bulb and even developing countries will become their standard LED bulbs important reference.
Wang Xi-day with four points summarize the core of the standard: 1) reduce the power factor threshold, help to reduce costs and expand sales of LED lights; 2) to highlight the low power LED bulbs directly replace incandescent lamps norms; 3) a clear LED light bulb efficiency of 55 lumens per watt, the bottom line; 4) a clear light decline after 25,000 hours with a limit of three bottom line.
Wang Xi-day stress that this is only with domestic 80lm per watt LED light efficiency is the result of statistics. There have been published abroad, 208 lumens per watt of the new LED products, incandescent only 15-25lm per watt efficiency with low light, so to replace incandescent lamps with LED is an inevitable trend.
LED industry chaos and worries
The rapid development of LED lighting, but the chaos, such as lamp life, and people think of thirty thousand hours. Wang Xi-day from the following aspects that must be faced by the industry to solve the problem:
1. To purchase high efficiency LED light unit, pay attention to high temperature by 60 ℃ measured the LED voltage and current data to filter. LED current was elected for the same series, the same LED voltage was selected for association. At present the workshop-style LED lights civil works, if done after the purchase of 60 ℃ LED temperature screening, we can have confidence in a process advancing down, otherwise it will cause a lot of quality problems.
2. Low-power LED lights, LED string can be, and required constant current power supply; and in high-power LED series LED lamps were to be more constant power supply, which is more complicated; there both string and and the grid network structure of the LED matrix, must be both constant current and voltage regulator power to do.
3.LED sworn enemy is the heat lamp, LED module IV characteristics at different temperatures are quite different. So in addition to screening under the conditions of 60 ℃ for LED LED series and parallel, respectively, but also need to have temperature monitoring and compensation measures can only be controlled by cooling the temperature rise of LED light bulbs as small as possible. LED light efficiency is lower the higher the temperature, light efficiency and inversely proportional to temperature; LED temperature is higher the greater light decline, life expectancy is inversely proportional to temperature. No exaggeration to say, who mastered the LED light bulb cost-effective cooling, good structure, whoever got the advantage of LED lighting industry with confidence. LED light power adapter, note the electrolytic capacitor on the temperature-sensitive device: civilian electrolytic capacitor signs 85 ℃; industrial electrolytic capacitor temperature signs 105 ℃; professional products electrolytic capacitor logo temperature above 125 ℃. -Money, high reliability, electrolytic capacitors to be started from the purchase of careful attention.
4.LED lamps is the combination of science and art, including light, "illumination" (lux as a unit, such as corridors, 15 lux lamp on it, a desk and desktop, the need for the church was satisfied more than 60 lux). There are "color temperature" of the "color" and the need for more optical dimming requirements, meet the eye and psychological needs. For these purposes, LED lamp itself, the need for power electronics and thermodynamics considerations, and overall size requirements and cost limitations and restrictions. So, LED industry, entry is easy, the threshold is not high, prone to herd, run into the arts, optics, electricity, thermodynamics specific issues, in turn a number of Road Goukan, once a reshuffle.
LED bulb orders now often requires more than 0.9 power factor, Wang Xi-day do not agree with such a request. Widespread use of electronic ballast fluorescent lamps, the formation of social consensus: the higher the better power factor. But in order to improve the power factor had to increase costs, which are detrimental to the production and marketing. Moreover, fluorescent lamps are low pressure arc discharge lamp, a negative resistance characteristics of the light source, the power of environmental protection (Harmonics), EMC problems are acute. However, LED light source is a positive resistance characteristic, LED lamp itself does not exist EMC problems, the service is only for the LED constant current power supply adapter. Such as switching power supply, only occur EMC problems. America Online generally harmonic power compensation devices, so 5W or less than 5W of LED light bulbs without the requirements of PF, even more than 5W of LED light bulbs, but also lowers the threshold of 0.7 or above only requires it. Do not add the same number of active power compensation APFC Power Supply (That will lead to EMC problems), the production costs are very favorable. This is to promote both production and sales of LED light bulbs Specifications purpose.
"No electrolytic capacitors program" promising
Now single LED factory specifications, in addition to lumens per watt light efficiency labeling index, there are very attractive long-life, the light fades before the thirty ten thousandths to over one hundred thousand hours of tens of thousands of long life. But in fact, some LED lights do not light a few days running, and some LED lights in a fit of thunderstorms, the full range of lights are not bright. Wang Xi-day emphasis on power reliability is very important to use "bucket theory" to explain. Reliability of electrolytic capacitors is the shortest of wood! If you want to improve the reliability of LED light bulbs must be faced up to removing the most unreliable short board, which is the current LED lamp industry in general desire to "no power adapter LED electrolytic capacitor "Technical support reasons.
Wang Xi-day said that Seoul Semiconductor has recently noted that publicity to launch a "communication LED", is said to be without electrolytic capacitor, but unfortunately has not got the sample, can not prove that it really no electrolytic capacitors. In addition, the company introduced a number of IC IC power not only to serve a large number of LED solutions do not require any components, the natural need of the electrolytic capacitors. Some companies are trying to research in high-power LED light power adapter, also claimed that no electrolytic capacitors, are receiving large orders.
Vertical power electronics, the electrolytic capacitor is only the peak charge storage to prepare for the subsequent short-term release of stored charge. So you can think of the energy storage inductor, the Chinese nuclear fusion device is a very large storage of energy, while the use of the "superconducting inductive energy storage," which, "capacitor energy storage", supplemented by the match. Two power electronics based solutions that boost has excellent effects of the "Post" (Boost) and blood pressure have the advantage of the "Buck" (BUCK), are the core of high-frequency inductors as energy storage, combined with electrolytic capacitors for the smooth ripple. Wang Xi-day that if the use of power electronics technology to the ripple can be achieved is small enough, then no electrolytic capacitor to smooth the ripple is expected to be and things.
Limited to the company's patent, Wang Xi-day in the eyes of the "no electrolytic capacitors" High reliability LED power adapter program are as follows:
(1) multi-phase rectified DC output with low ripple envelope and the zero solution, however.
(2) the frequency of high-frequency multi-phase rectifier as high (Shaw diodes subject to delay and synchronous rectifier FET switch delay), then the output of the DC envelope more smooth, do not use electrolytic capacitors.
(3) single-phase AC power rectifier, AC power with the same frequency, but ninety degrees phase shift AC rectifier synthesis, but also zero-ripple, with a small non-electrolytic capacitors to smooth ripple.
(4) single-phase AC power rectifier with a switch (instead of the entire comb with a diode) into the AC circuit in the third harmonic is also significantly reduced ripple effect.
(5) with transformer ripple frequency offset can already reverse engineering utility. Particularly suitable for high current load applications.
(6) above (5) If the load current is not too great, and very strict requirements on the ripple, may wish to back with a low dropout electronic filter, in principle, to meet any of the ripple-sensitive users, but high cost , efficiency is also affected.
(7) Power Electronics negative feedback reduces ripple.
(8) above (7) with the single chip the same size in the opposite direction produces the ripple of the "digital initiative to offset the ripple" program is a promising one of the options.
(9) to play the electric LED - light response is nanoseconds (ns) level advantage of using the delay characteristics of the human eye retina, in less than 0.1 milliseconds (not less than 10KHz) of the comb with a similar kind of pulse Driving LED light, intermittent light were not seeing that the LED light flashes. This is a further significant than the DC power-saving LED lights program, many units are working to research, and that this is one of the options do not need to electrolytic capacitors.
(10) Two parallel LED back lighting with cross-frequency constant alternating current, each LED lamp single light work of high-frequency half-wave light, rest, half-wave does not emit light nor heat, the next LED after substantial price cuts, is to lower the cost of implementation.
Finally, Wang Xi-day summary of the LED industry, Difficulties and Solutions.
1) The local LED industry, where early research each company's "factory standard" by many local enterprises of the many "factory standard" collective wisdom. LED in the local association or other civil society organizations, forming "local LED industry norms", the introduction of a "national standard" in future. Energy Star, like the United States, as the introduction of more scientific and standardized Chinese characteristics LED bulbs! Have good rules into the radius.
2) to seize the "LED temperature" of this Niu Bizi make a good article.
3) take the "life of electrolytic capacitors and LED the gap between the" do more to match the reliability of long-life LED power supply LED.
4) Innovation is the core of the transformation: "I have no people, people I have gifted, gifted people I serve, who I am cheap and excellent service, innovation and price competition as a generation upgrade I have no ... ...."
