Associate Professor Wang Xitian of Guangxi University specializes in power supply design. In recent years, he has been actively involved in the design of LED power supplies , especially in the field of electroless capacitors. For the current difficulties and countermeasures of the LED lighting industry, Wang Xitian also has his own unique insights.
US Energy Star LED Bulbs Code Promotes Healthy Industrial Development
There are rumors circulating in the industry: "First-class profits are in standard setting, second-rate profits are in patent competition, third-rate profits are in brand-name strategy, and fourth-rate profits are price wars." The US Energy Star LED Bulb Specification announced in November 2009 has a milestone. significance. Although it is only in the US market to buy LED bulbs with the "US Energy Star Certification" logo, it will enjoy the US government's financial subsidies to buyers, but this is the first LED bulb specification that the global LED lamp industry can't care about. It will even become an important reference for countries to formulate their own LED bulb specifications in the future.
Wang Xitian summed up the core content of the standard in four sentences: 1. Lowering the threshold of power factor, helping to reduce costs and expanding production and sales of LED lights; 2. Highlighting the specification of direct replacement of incandescent lamps with small power LED bulbs; 3. Defining LED bulb light Effectiveness 55 lumens per watt; 4, clear 25000 hours after use, light decay three becomes the limit of the bottom line.
The direct replacement of incandescent bulbs with LED bulbs is of great significance. Combined with the current domestic chips, it has reached 80lm/W. In combination with the US Energy Star specification, the specifications for replacing incandescent bulbs with LED bulbs are as follows:
Electrolytic capacitors are not good for LED lighting price wars
Wang Xitian particularly emphasized that this is only the result of using 80mm light-effect statistics per watt of domestic LED. Foreign countries have announced new LED products with 208 lumens per watt. Incandescent lamps have only 15-25 lm per watt low light efficiency, so replacing incandescent lamps with LED lamps is an inevitable trend.
LED industry chaos and hidden worry
LED lighting is developing at a high speed, but it is like a mess. For example, the life of a lamp is not as long as 30,000 hours. Wang Xitian believes that the problems faced by the industry must be solved from the following aspects:
1. Purchase LED units with higher luminous efficiency, and pay attention to screening with LED voltage and current data measured at 60 °C high temperature. Selecting the LED with the same current is suitable for the series connection, and selecting the LED with the same voltage is suitable for the correlation. At present, the folk workshop-style LED lamp factory, if you do the 60°C high-temperature screening after LED purchase, can confidently proceed to the next process, otherwise it will cause many quality problems.
2, low-power LED lights, a string of LEDs can be used, need to use constant current power supply; and medium and high-power LED lights need multiple strings of LEDs to supply constant current, which is more complicated; there are both strings and The square matrix of the square network structure must be both constant current and regulated power supply.
3, the enemy of LED lights is high temperature, the volt-ampere characteristics of LED units are quite different at different temperatures. Therefore, in addition to screening LEDs at 60 ° C for LED series and parallel respectively, temperature monitoring and compensation is required to control the temperature rise of LED bulbs as small as possible. The higher the LED temperature, the lower the light efficiency, and the light effect is inversely proportional to the temperature; the higher the LED temperature, the greater the light decay, and the lifetime is inversely proportional to the temperature. It is no exaggeration to say that whoever has mastered the cost-effective and excellent structure of LED bulb cooling, whoever has the confidence guarantee of the dominant LED lamp industry. In the LED light power adapter, pay attention to the temperature-sensitive device of electrolytic capacitor: 85 °C for civil electrolytic capacitors; 105 °C for industrial electrolytic capacitors; 125 °C for professional-grade electrolytic capacitors. For a penny of goods, high reliability requires careful attention from the purchase of electrolytic capacitors.
4, LED lamps are a combination of science and art, including the lighting "illuminance" (luxe units, such as 15 lux under the corridor lights, desks and church tables need to be more than 60 lux to be satisfied). There is also the "color rendering" of "color temperature" and the need for optical requirements such as dimming to meet eye and psychological needs. For the above purposes, LED lamps themselves need to be considered in terms of power electronics and thermodynamics, and overall, there are cost constraints and volume requirements. Therefore, the LED industry is easy to get started, the threshold is not high, and it is easy to happen. When encountering the above-mentioned specific problems of art, optics, electricity and thermodynamics, there will be many gullies and shuffling once and for all.
Today's LED bulb orders often require power factors greater than 0, 9, Wang Xitian does not agree with this requirement. Fluorescent electronic ballasts are widely used, forming a social consensus: the higher the power factor, the better. However, in order to increase the power factor, the cost has to be increased, which is unfavorable for both production and sales. In addition, the fluorescent lamp is a low-pressure arc discharge lamp, which is a light source with negative resistance characteristics, and is very prominent for the environmental protection (harmonic problem) and EMC problem of the power supply. However, LED is a light source with positive resistance characteristics. The LED lamp itself does not have EMC problems, and is only a constant current adaptive power supply for LED services. If a switching power supply is used, the EMC problem occurs. The US power grid generally has an online harmonic compensation device, so there is no PF requirement for a 5W or less 5W LED bulb. Even if the LED bulb exceeds 5W, the threshold is reduced to only 0, 7 or above. It is not necessary to add active power equal-quantity compensation APFC switching power supply (which will cause EMC problems), which is very beneficial to the reduction of production cost. This is the normative purpose of promoting the production and sales of LED bulbs.
"Electro-less capacitor solution" is promising
Now, the single LED factory manual, in addition to the luminous efficiency per watt lumen indicator, there is a very attractive long life, tens of thousands to more than 100,000 hours of long life before the light decay of 30. But in fact, some LED lights do not light up in a few days, and some LED street lights are not lit after a thunderstorm. Wang Xitian emphasized that power supply reliability is very important and can be explained by the "wooden barrel principle". Electrolytic capacitors are the least reliable strips! If you want to improve the reliability of LED bulbs, you must be determined to remove the most unreliable short board. This is the reason why the LED lighting industry is generally eager to support the "LED power adapter without electroless capacitors".
Wang Xitian said that he recently noticed that Seoul Semiconductor of South Korea promoted an "AC LED", which is said to be without electrolytic capacitors. Unfortunately, no samples have been obtained so far, and it is impossible to prove whether it is really an electroless capacitor. In addition, many IC companies have introduced an IC solution that does not require much power, and does not require any components. Naturally, electrolytic capacitors are not needed. There are also some companies that are working hard to tackle the high-power LED light power adapter, and also claim that they do not need electrolytic capacitors and are accepting large orders.
In the case of vertical power electronics, electrolytic capacitors simply store peak charge for subsequent short-term discharge of stored charge. Therefore, the inductor can also store energy. China's nuclear fusion equipment needs to store very large energy. At the same time, it uses “superconducting energy storage†and “capacitor energy storage†as a supplement. The two basic schemes of power electronics, Boost, which has excellent effects in boosting, and BUCK, which has advantages in bucking, use high-frequency inductors as the energy storage core, supplemented by electrolytic capacitors. Smooth ripple. Wang Xitian believes that if the power electronics technology can achieve a sufficiently small ripple, then it is impossible to smooth the ripple without using electrolytic capacitors.
Limited to the patents of various companies, Wang Xitian’s solution for the “electroless capacitor†high reliability LED power adapter is as follows:
(1) The multi-phase rectified output DC envelope is a low ripple and not zero solution.
(2) The frequency of the multiphase rectification high frequency is as high as possible (limited by the Shore diode delay and the synchronous rectification FET switch delay), the smoother the output DC envelope is, and the electrolytic capacitor is not needed.
(3) Single-phase AC rectification, the AC rectification combined with the same frequency as the AC power supply but with a phase shift of 90 degrees is also zero, and the non-electrolyte small capacitor can smooth the ripple.
(4) The three-phase harmonics injected into the circuit of the single-phase AC power switch (rather than the diode comb) also significantly reduce the ripple effect.
(5) It is engineering and practical to reverse the high frequency ripple with the transformer. Particularly suitable for high current load applications.
(6) The above (5) If the load current is not too large, and the ripple requirement is very strict, it may be followed by a low-dropout electronic filter. In principle, it can satisfy any user sensitive to ripple, but the cost is high. Efficiency is also affected.
(7) Power electronic negative feedback technology can reduce ripple.
(8) The above-mentioned (7) "digital active cancellation ripple" scheme with the same size and opposite direction of ripple generated by the single-chip microcomputer is one of the promising solutions.
(9) The electro-optical response of the LED is an advantage of the nanosecond (ns) level. Using the delay characteristic of the retina of the human eye, a pulse like a comb is used within a period shorter than 0, 1 millisecond (not less than 10 kHz). To drive the LED light, the human eye can't see the intermittent light, that is, the LED light flashes. This is a plan to further save power than DC LED lamps. Many units are working hard to solve the problem, which is one of the solutions that do not require electrolytic capacitors.
(10) Two LEDs are connected in reverse parallel with AC constant current AC lighting. Each LED lamp operates with a high-frequency half-wave illumination. The rest of the half-wave does not emit light or heat. In the future, after the LED is greatly reduced, it can be low. Cost implementation plan.
Difficulties and countermeasures in the LED industry
(1) All localities investigate the “factory standard†of each local LED industry enterprise early, and gather many “factory labels†from many local enterprises to gather ideas. In the local LED association or other non-governmental organizations, the formation of "local LED industry norms", to lay the foundation for the introduction of the "national standard." Like the US Energy Star, the introduction of more scientific Chinese LED bulb specifications, there are rules and regulations.
(2) Grab the "LED temperature" and make a good article.
(3) Grasp the "difference between electrolytic capacitor and LED life" to make more reliable LED power supply to match long-life LED lights.
(4) The core of the transformation lies in innovation: "There is no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one."
US Energy Star LED Bulbs Code Promotes Healthy Industrial Development
There are rumors circulating in the industry: "First-class profits are in standard setting, second-rate profits are in patent competition, third-rate profits are in brand-name strategy, and fourth-rate profits are price wars." The US Energy Star LED Bulb Specification announced in November 2009 has a milestone. significance. Although it is only in the US market to buy LED bulbs with the "US Energy Star Certification" logo, it will enjoy the US government's financial subsidies to buyers, but this is the first LED bulb specification that the global LED lamp industry can't care about. It will even become an important reference for countries to formulate their own LED bulb specifications in the future.
Wang Xitian summed up the core content of the standard in four sentences: 1. Lowering the threshold of power factor, helping to reduce costs and expanding production and sales of LED lights; 2. Highlighting the specification of direct replacement of incandescent lamps with small power LED bulbs; 3. Defining LED bulb light Effectiveness 55 lumens per watt; 4, clear 25000 hours after use, light decay three becomes the limit of the bottom line.
The direct replacement of incandescent bulbs with LED bulbs is of great significance. Combined with the current domestic chips, it has reached 80lm/W. In combination with the US Energy Star specification, the specifications for replacing incandescent bulbs with LED bulbs are as follows:
Electrolytic capacitors are not good for LED lighting price wars
Wang Xitian particularly emphasized that this is only the result of using 80mm light-effect statistics per watt of domestic LED. Foreign countries have announced new LED products with 208 lumens per watt. Incandescent lamps have only 15-25 lm per watt low light efficiency, so replacing incandescent lamps with LED lamps is an inevitable trend.
LED industry chaos and hidden worry
LED lighting is developing at a high speed, but it is like a mess. For example, the life of a lamp is not as long as 30,000 hours. Wang Xitian believes that the problems faced by the industry must be solved from the following aspects:
1. Purchase LED units with higher luminous efficiency, and pay attention to screening with LED voltage and current data measured at 60 °C high temperature. Selecting the LED with the same current is suitable for the series connection, and selecting the LED with the same voltage is suitable for the correlation. At present, the folk workshop-style LED lamp factory, if you do the 60°C high-temperature screening after LED purchase, can confidently proceed to the next process, otherwise it will cause many quality problems.
2, low-power LED lights, a string of LEDs can be used, need to use constant current power supply; and medium and high-power LED lights need multiple strings of LEDs to supply constant current, which is more complicated; there are both strings and The square matrix of the square network structure must be both constant current and regulated power supply.
3, the enemy of LED lights is high temperature, the volt-ampere characteristics of LED units are quite different at different temperatures. Therefore, in addition to screening LEDs at 60 ° C for LED series and parallel respectively, temperature monitoring and compensation is required to control the temperature rise of LED bulbs as small as possible. The higher the LED temperature, the lower the light efficiency, and the light effect is inversely proportional to the temperature; the higher the LED temperature, the greater the light decay, and the lifetime is inversely proportional to the temperature. It is no exaggeration to say that whoever has mastered the cost-effective and excellent structure of LED bulb cooling, whoever has the confidence guarantee of the dominant LED lamp industry. In the LED light power adapter, pay attention to the temperature-sensitive device of electrolytic capacitor: 85 °C for civil electrolytic capacitors; 105 °C for industrial electrolytic capacitors; 125 °C for professional-grade electrolytic capacitors. For a penny of goods, high reliability requires careful attention from the purchase of electrolytic capacitors.
4, LED lamps are a combination of science and art, including the lighting "illuminance" (luxe units, such as 15 lux under the corridor lights, desks and church tables need to be more than 60 lux to be satisfied). There is also the "color rendering" of "color temperature" and the need for optical requirements such as dimming to meet eye and psychological needs. For the above purposes, LED lamps themselves need to be considered in terms of power electronics and thermodynamics, and overall, there are cost constraints and volume requirements. Therefore, the LED industry is easy to get started, the threshold is not high, and it is easy to happen. When encountering the above-mentioned specific problems of art, optics, electricity and thermodynamics, there will be many gullies and shuffling once and for all.
Today's LED bulb orders often require power factors greater than 0, 9, Wang Xitian does not agree with this requirement. Fluorescent electronic ballasts are widely used, forming a social consensus: the higher the power factor, the better. However, in order to increase the power factor, the cost has to be increased, which is unfavorable for both production and sales. In addition, the fluorescent lamp is a low-pressure arc discharge lamp, which is a light source with negative resistance characteristics, and is very prominent for the environmental protection (harmonic problem) and EMC problem of the power supply. However, LED is a light source with positive resistance characteristics. The LED lamp itself does not have EMC problems, and is only a constant current adaptive power supply for LED services. If a switching power supply is used, the EMC problem occurs. The US power grid generally has an online harmonic compensation device, so there is no PF requirement for a 5W or less 5W LED bulb. Even if the LED bulb exceeds 5W, the threshold is reduced to only 0, 7 or above. It is not necessary to add active power equal-quantity compensation APFC switching power supply (which will cause EMC problems), which is very beneficial to the reduction of production cost. This is the normative purpose of promoting the production and sales of LED bulbs.
"Electro-less capacitor solution" is promising
Now, the single LED factory manual, in addition to the luminous efficiency per watt lumen indicator, there is a very attractive long life, tens of thousands to more than 100,000 hours of long life before the light decay of 30. But in fact, some LED lights do not light up in a few days, and some LED street lights are not lit after a thunderstorm. Wang Xitian emphasized that power supply reliability is very important and can be explained by the "wooden barrel principle". Electrolytic capacitors are the least reliable strips! If you want to improve the reliability of LED bulbs, you must be determined to remove the most unreliable short board. This is the reason why the LED lighting industry is generally eager to support the "LED power adapter without electroless capacitors".
Wang Xitian said that he recently noticed that Seoul Semiconductor of South Korea promoted an "AC LED", which is said to be without electrolytic capacitors. Unfortunately, no samples have been obtained so far, and it is impossible to prove whether it is really an electroless capacitor. In addition, many IC companies have introduced an IC solution that does not require much power, and does not require any components. Naturally, electrolytic capacitors are not needed. There are also some companies that are working hard to tackle the high-power LED light power adapter, and also claim that they do not need electrolytic capacitors and are accepting large orders.
In the case of vertical power electronics, electrolytic capacitors simply store peak charge for subsequent short-term discharge of stored charge. Therefore, the inductor can also store energy. China's nuclear fusion equipment needs to store very large energy. At the same time, it uses “superconducting energy storage†and “capacitor energy storage†as a supplement. The two basic schemes of power electronics, Boost, which has excellent effects in boosting, and BUCK, which has advantages in bucking, use high-frequency inductors as the energy storage core, supplemented by electrolytic capacitors. Smooth ripple. Wang Xitian believes that if the power electronics technology can achieve a sufficiently small ripple, then it is impossible to smooth the ripple without using electrolytic capacitors.
Limited to the patents of various companies, Wang Xitian’s solution for the “electroless capacitor†high reliability LED power adapter is as follows:
(1) The multi-phase rectified output DC envelope is a low ripple and not zero solution.
(2) The frequency of the multiphase rectification high frequency is as high as possible (limited by the Shore diode delay and the synchronous rectification FET switch delay), the smoother the output DC envelope is, and the electrolytic capacitor is not needed.
(3) Single-phase AC rectification, the AC rectification combined with the same frequency as the AC power supply but with a phase shift of 90 degrees is also zero, and the non-electrolyte small capacitor can smooth the ripple.
(4) The three-phase harmonics injected into the circuit of the single-phase AC power switch (rather than the diode comb) also significantly reduce the ripple effect.
(5) It is engineering and practical to reverse the high frequency ripple with the transformer. Particularly suitable for high current load applications.
(6) The above (5) If the load current is not too large, and the ripple requirement is very strict, it may be followed by a low-dropout electronic filter. In principle, it can satisfy any user sensitive to ripple, but the cost is high. Efficiency is also affected.
(7) Power electronic negative feedback technology can reduce ripple.
(8) The above-mentioned (7) "digital active cancellation ripple" scheme with the same size and opposite direction of ripple generated by the single-chip microcomputer is one of the promising solutions.
(9) The electro-optical response of the LED is an advantage of the nanosecond (ns) level. Using the delay characteristic of the retina of the human eye, a pulse like a comb is used within a period shorter than 0, 1 millisecond (not less than 10 kHz). To drive the LED light, the human eye can't see the intermittent light, that is, the LED light flashes. This is a plan to further save power than DC LED lamps. Many units are working hard to solve the problem, which is one of the solutions that do not require electrolytic capacitors.
(10) Two LEDs are connected in reverse parallel with AC constant current AC lighting. Each LED lamp operates with a high-frequency half-wave illumination. The rest of the half-wave does not emit light or heat. In the future, after the LED is greatly reduced, it can be low. Cost implementation plan.
Difficulties and countermeasures in the LED industry
(1) All localities investigate the “factory standard†of each local LED industry enterprise early, and gather many “factory labels†from many local enterprises to gather ideas. In the local LED association or other non-governmental organizations, the formation of "local LED industry norms", to lay the foundation for the introduction of the "national standard." Like the US Energy Star, the introduction of more scientific Chinese LED bulb specifications, there are rules and regulations.
(2) Grab the "LED temperature" and make a good article.
(3) Grasp the "difference between electrolytic capacitor and LED life" to make more reliable LED power supply to match long-life LED lights.
(4) The core of the transformation lies in innovation: "There is no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one, no one."
Small computer system interface (SCSI) is an independent processor standard for system level interfaces between computers and intelligent devices (hard disks, floppy drives, optical drives, printers, scanners, etc.). SCSI is an intelligent universal interface standard.
In addition to SCSI, IDE is also a very common interface. From the point of view of ease of use, IDE is more suitable for ordinary users. In addition, personal computer users not only need to configure a few peripherals, but also do not require high speed. Therefore, it is more appropriate to choose IDE interface. In addition, IDE also has the characteristics of high performance price ratio and wide application. Although the SCSI interface has many incomparable characteristics, the price of the interface and its peripherals is too expensive to be borne by ordinary users, which determines the limitation of its actual use range.
1. The working mode of IDE requires the whole process participation of CPU. When the CPU reads and writes data, it can't perform other operations. In this case, in the multitask operating system of Windows 95 / NT, the system reaction will be greatly slowed down. The SCSI interface controls the data reading and writing operation completely through the independent high-speed SCSI card, so the CPU does not have to waste time to wait, which obviously can improve the overall performance of the system. However, IDE interface has also made great improvements to improve this problem. DMA mode can be used instead of PIO mode to read and write data. DMA channel is responsible for data exchange, which greatly reduces the CPU consumption. However, comparing the CPU utilization of SCSI and IDE, we can find that SCSI still has considerable advantages.
2. The scalability of SCSI is larger than that of IDE. Generally, each ide system can have two IDE channels, with a total of four IDE devices. The SCSI interface can connect 7-15 devices, much more than IDE, and the cable connected is far longer than ide.
3. Although the price of SCSI device is higher, compared with IDE, the performance of SCSI is more stable, durable and reliable.
SCSI Solder Type Section
ShenZhen Antenk Electronics Co,Ltd , https://www.antenkcon.com