Although the LED prospects are now being heated up, the relevant data shows that in the general lighting market, which is dominated by light bulbs and fluorescent tubes, recessed lights, street lights and parking lights, and work lights (table lamps, cabinet lighting). The proportion of LED lighting applications is still less than 1%. Taking outdoor LED street lighting as an example, most of them are only used as government demonstration projects. The real commercial popularity seems to take time.
Zheng Zongqian, senior application manager of OnSemi Hong Kong and China, believes that the reason why LED street lamps can be used as demonstration projects depends on their high luminous efficiency, low reflection loss of lamps, no need for high pressure, no mercury, and higher safety. Secondly, compared with ordinary lighting, LED lamps are easier to add digital or analog dimming functions, which is convenient for remote control, and can provide ultra-high brightness and color rendering in special cases such as foggy and rainy days. In addition, LED street lights are significantly superior to high-pressure sodium lamps in terms of laying costs, power consumption costs, and life.
At the same time, however, the relatively high cost, low reliability of the power supply, and short range, which are not conducive to working at higher heights, are still important factors hindering the rapid development of LED street lights. On the other hand, if the government can introduce LED road lighting standards in time, it will be a very powerful means to popularize LED street lights.
Li Yingyou, senior manager of Fairchild's PLM lighting technology marketing, said that LED street lighting is part of the government's energy efficiency program. The upgrade includes not only replacement of light bulbs, but also the use of long-life rectifiers. “The first step in the upgrade is to install LED streetlights in the newly developed area and then gradually replace the existing old streetlights. It is expected that most of today's streetlights will be replaced by LED lighting in the next five years.â€
Zhang Jing, sales manager of ADI Central China, believes that compared with outdoor lighting, LED indoor lighting is in its infancy, and the current cost performance is not high. This is because the lumen cost is too high, and on the other hand, LED indoor lighting products. There are too few types, lighting designers have no choice but to set an obstacle to the promotion of indoor lighting products. His suggestion is that the development and promotion of LED indoor lighting products should focus on product family, integration, intelligence and humanization, improve luminous efficiency and luminous flux utilization, and minimize overall integrated lighting costs.
Challenge keywords: "hot", "drive" and "cost"
According to PieroBianco, Maxim's business manager, “frame size†and “electrical compatibility†are key factors in the success of LED lights. “The reason is simple. The replacement lamp must be able to be installed in the frame of the previous lamp source. Of course, it must also work properly on the existing electrical structure to ensure that no light flashes.â€
He further explained that the existing framework imposes physical limitations on the replacement lamp (ie, the drive board must be small enough) and thermal limit requirements. These factors constrain the designer's ability to change lighting options (such as PAR, R, and A specifications), and the smaller the size, the more difficult the application faces, such as MR16 and GU10. Thermal constraints are often more critical than size factors. Because, unlike other technologies, LEDs emit only visible light and do not generate infrared radiation energy. Therefore, LEDs are more energy efficient than incandescent or halogen lamps, and most of the heat is dissipated through the inner conductor of the lamp.
"Considering that heat dissipation is a key factor that limits the light intensity of the lamp, the LED technology currently used in lighting replacement products is difficult to reach the brightness level acceptable to the mainstream market. Therefore, in order to break through the brightness limit, it is necessary to solve the heat dissipation problem. This is also an indispensable condition for the product to successfully commercialize." Piero stressed.
The effect of heat dissipation is not only the light intensity, but also directly affects the service life of the drive board. Piero said that in order to emit higher light, the lights must work at fairly high temperatures (+80 ° C to +100 ° C). At this temperature, the life of the driver board will limit the performance of the entire lamp, especially electrolytic capacitors become a difficult problem in design. Because electrolytic capacitors dry quickly at high temperatures, their working life does not exceed thousands of hours, which is a factor that limits the life of the entire lamp.
Tony Armstrong, director of marketing for Power Products at Linear, analyzed that the choice of LED driver circuitry is highly dependent 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. “But regardless of the topology, optimized LED drivers are very important for the reliability and longevity of LED products.â€
In Zheng Zongqian's view, in addition to the current LED light quality compared with traditional lighting, there is still a gap, another problem that cannot be ignored is that LED lighting is related to the complicated design of electricity, light, heat and machinery. The unified design standards directly lead to the uneven quality of LED lighting products on the market, which is one of the reasons why it is difficult to be accepted by the public in the short term.
In addition to the difficulties and challenges mentioned in the article, the cost pressure can of course not be avoided. In this regard, both Zheng Zongqian and Li Yingyou said: "Compared with traditional lighting used CFL lamps or incandescent lamps, the current price of LED lamps is still expensive, which also greatly hinders the development of LED lighting. High reliability is becoming an LED At the same time, the key factors of lighting also increase the system cost pressure."
LED lighting solutions
Piero highlights Maxim's LED driver solutions for 120VAC/230VAC input and 12VAC input illuminators. It is reported that this type of scheme adopts single-stage conversion. By shaping the input current, the illumination lamp can be prevented from flickering in the dimming state, and is compatible with the two-way three-terminal thyristor and the trailing edge dimmer and the electronic transformer. design. On the other hand, since there is no need for electrolytic capacitors, it not only helps to reduce the size of the solution, but also enables the driver board to be mounted in a small-sized lamp frame, and can extend the life of the LED lamp from less than 10,000 hours to 90 degrees. 000 hours.
Li Yingyou recommends four topological solutions based on the power rating of the application:
* Since small PCB area and low BOM cost are important factors in the use of ball-embedded bulbs, the PSR flyback solution is targeted at low power applications ("15W"). Its unique selling point is Fairchild's proprietary TRUECURRENT technology, which reduces CC/CV variation to +-5% and eliminates the need for a secondary-side feedback circuit and optional internal MOSFET devices to reduce PCB size.
* The single-stage PFC flyback solution with CRMPFC controller is targeted at mid-range power applications (40W) and is said to support high efficiency, high power factor, low THD and low bill of material costs.
* For high power applications (40W~), the PFC+ flyback solution for 100W applications and the PFC+LLC half bridge solution for 100W applications are good choices. And the latter can increase the efficiency to over 90% due to the use of zero voltage switching (ZVS) technology.
ON Semiconductor also has an LED general lighting solution for different power AC-DC power supplies. Take its NCL3000 as an example. This is a single-stage power factor correction TRIAC dimmable LED driver for residential and commercial AC-DC powered LED lighting applications with 8W-25W power, using a CrM flyback architecture in a single segment. The topology provides a high power factor greater than 0.95, thus eliminating the DC-DC conversion section. In addition, the single-stage PFCLED driver NCL30001, CrMPFC+QRPWM driver NCP1607+NCP1377, and CrMPFC+LLCPWM driver NCP1607+NCP1397 or NCP1392/3 are mainly for power "50W street lighting and high-power area lighting applications, typical energy efficiency can exceed 92 %.
ADI will focus on AD converters, and its various 12-16-bit ADCs are suitable for LED streetlights and indoor lighting applications. For example: AD7457, AD7466, and AD7153, AD7745 to achieve CDC (capacitance to digital conversion) function, can achieve automatic switching of LEDs, to achieve power saving function.
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