LED general lighting commercialization process and solution

Under the trend of energy conservation and environmental protection, LED lighting has become the target of many regulatory agencies. For example, the solid state lighting standard for the 1.1 version of the “Energy Star” program of the US Department of Energy was effective in February 2009. The China National Institute of Standardization is also expected to be ready in 2010. Released the Chinese version of LED lighting energy efficiency standards. It is estimated that by 2012, the market size of LED drivers and related discrete devices will increase from approximately US$688 million in 2008 to US$1.308 billion, with a compound annual growth rate of 17.4%.

LED general lighting is still in its infancy

Although the LED prospects are now getting hotter, relevant data show that in the general lighting market, where light bulbs and fluorescent tubes are replaced, downlights, street and stop lights, work lights (table lamps, cabinet lighting), etc. The proportion of LED lighting applications is still less than 1%. Taking outdoor LED street lighting as an example, most of them are currently only used as government demonstration projects. The real commercialization seems to take some time.

Zheng Zongqian, senior application manager of OnSemi Hong Kong and China, believes that LED street lamps can be used as demonstration projects, of course, first of all depends on their high luminous efficiency, low reflection loss of lamps, no need for high pressure, no mercury, and higher safety. Secondly, compared to ordinary lighting, LED lamps are easier to incorporate digital or analog dimming functions to facilitate remote control, and can provide ultra-high brightness and color rendering in special conditions such as fog and rain. In addition, LED street lamps are significantly better than high-pressure sodium lamps in terms of laying costs, power consumption costs, and longevity.

However, at the same time, its relatively high cost, poor reliability of the power supply, and short range, which is not conducive to working at higher altitudes, are still important factors that hinder the rapid development of LED street lamps. On the other hand, if the government can promptly introduce LED road lighting standards, then it will be a very powerful means of popularizing LED street lamps.

Lee Ying-woo, a senior marketing manager for Fairchild PLM lighting technology, said that the use of LED street lighting is part of the government's energy efficiency project. Upgrades include not only replacing light bulbs but also using long-lived rectifiers. “The first step in the upgrade is to install LED street lights in newly developed areas, and then gradually replace the existing old street lighting. It is expected that most of the street lights will be replaced by LED lighting in the next five years.”

Zhang Jing, sales manager of ADI Central China, believes that compared to outdoor lighting, LED interior lighting is at the initial stage, the current cost is not high, this is because the lumen cost is too high, on the other hand is also because of LED indoor lighting products Too few species, lighting designers are struggling to choose, and set obstacles for 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 humanity, improve luminous efficiency and luminous flux utilization, and minimize the overall cost of lighting.

Challenge Keywords: "Hot," "Drive," and "Cost."

Piero Bianco, business manager of Maxim, believes that "outside dimensions" and "electrical compatibility" are key factors in the success of LED lights. “The reason is very simple. The replacement lamp must be able to be installed in the framework of the pre-light source. Of course, it must also be able to work on the existing electrical architecture to ensure that the light will not flicker.”

He further explained that the existing framework imposes physical restrictions on the replacement lamp (ie, the drive plate must be small enough) and thermal limiting requirements. These factors constrain the designer's changing lighting conditions (for example, PAR, R, and A specifications), and the smaller the size of the application, the more difficult it faces, such as MR16 and GU10. Thermal constraints are often more critical than size factors because, unlike other technologies, LEDs only emit 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 lamp's internal conductors.

“Considering that heat dissipation is a key factor that restricts the light intensity of the lamp, the LED technology currently used in lighting replacement products is difficult to reach the brightness level acceptable in the mainstream market. Therefore, in order to break the brightness limit, it is necessary to solve the heat dissipation problem. This is also an essential condition for the successful commercialization of the product,” Piero stressed.

The effect of heat dissipation is not only light intensity, but also directly affects the drive.

The service life of the moving plate. Piero said that in order to emit a higher light intensity, the light must work at a fairly high temperature (+80°C to +100°C). At this temperature, the life of the driver board will limit the performance of the entire lamp, especially the electrolytic capacitor becomes a thorny issue for the design. Because electrolytic capacitors dry quickly at high temperatures, their working life does not exceed thousands of hours, which has also become a factor that limits the service life of the entire lamp.

Tony Armstrong, director of product marketing for linear power products at Linear, analyzed that the choice of LED driver circuit depends 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 leads to a variety of different possible LED driver topologies. "But regardless of topology, optimized LED drivers are very important for the reliability and longevity of LED products."

In Zheng Zongqian's view, in addition to the current gap between LED light quality and traditional lighting, another problem that cannot be overlooked is that due to the complex design of LED lighting related to electricity, light, heat and machinery, the current lack of Uniform design standards directly lead to uneven quality of LED lighting products on the market. This is one of the reasons why it is difficult to be accepted by the general public in the short term.

In addition to the difficulties and challenges mentioned in the article, cost pressure cannot be avoided, of course. In this regard, both Zheng Zongqian and Li Yingyou said: “Compared to traditional lighting using CFL lamps or incandescent lamps, the current price of LED lamps is still expensive, and it has also hindered the development of LED lighting to a large extent. High reliability is becoming an LED. While lighting is a key factor, it also increases system cost pressures."

LED Lighting Solutions

Piero highlighted Maxim's LED driver solution for 120VAC/230VAC input and 12VAC input lamps. It is reported that this type of program uses a single-stage conversion. By shaping the input current, the lamp can be prevented from flickering in the dimming state, and is compatible with bidirectional three-terminal thyristors and trailing edge dimmers and electronic transformers. design. On the other hand, because there is no need for electrolytic capacitors, it not only helps to reduce the size of the program, allows the driver board to be installed in a small-sized retrofit lamp frame, and can also extend the lifespan of the LED lamp from normally less than 10,000 hours to 90 hours. 000 hours.

Li Yingyou proposed to select four topology solutions based on the power rating of the application:

*Because small PCB area and low BOM cost are important factors for using ball-type embedded light bulbs, PSR flyback solutions are mainly aimed at low-power applications ("15W"). Its unique selling point is Fairchild's proprietary TRUECURRENT technology that reduces CC/CV variation to +-5% without the need for a secondary-side feedback circuit and the option of a built-in MOSFET device to reduce PCB size.

* Single-stage PFC flyback solutions with CRMPFC controllers are primarily targeted at medium-range power applications (40W) and are said to support high efficiency, high power factor, low THD, and low BOM cost.

*For high power applications (40W~), the PFC+LLC half-bridge solution for 100W applications and 100W applications is a good choice. The latter, thanks to the Zero Voltage Switching (ZVS) technology, can increase the efficiency to more than 90%.

ON Semiconductor also has LED general lighting solutions for different AC-DC Power Supplies. Take the 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 to a single stage The topology provides a high power factor greater than 0.95, thus eliminating the DC-DC conversion section. In addition, the single-stage PFC LED 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, and the typical energy efficiency can exceed 92%.

ADI will focus on the AD converter, its a variety of 12-16-bit ADC are suitable for LED street lighting and indoor lighting applications. For example: AD7457, AD7466, and AD7153, AD7745 realize CDC (capacitive to digital conversion) function, can realize LED automatic switch, achieve the power-saving function.