In recent years, lighting has become an important area for countries around the world to promote energy conservation and environmental protection. According to statistics, about 20% of the world's electricity is used for lighting every year, and about 40% of this energy is used for inefficient incandescent lighting. With the continuous improvement of LED in almost every aspect of light output performance, cost, etc., LED general illumination has become a very attractive alternative solution for traditional lighting such as incandescent lamps.
Typical LED general lighting applications include bulb and fluorescent tube replacement, recessed lights, street and parking lights, work lights, landscape lighting, billboard text circuits, building lighting, and more. LED street lights have higher power, generally between 50W and 300W; LED building and area lighting applications typically range from 40W to 125W, which is a medium power range; below 30W can be collectively referred to as low power LED lighting applications, including Specific pointing lighting, such as cabinet lighting, recessed lights, spotlights PAR20/30/38 lighting replacement, table lamps, etc., and omnidirectional lighting, such as accent lighting, home appliances, general lighting A-type lamp replacement, decorative lighting and ceiling fan lights, etc. . This article will focus on low-power LED general-purpose lighting applications with powers below 30W and the corresponding energy-efficient solutions from ON Semiconductor.
Factors to consider when selecting a driver for low-power LED lighting applications
The main function of the LED driver is to limit the current under operating conditions, regardless of the input and output conditions. Its application design faces a variety of constraints, such as high energy efficiency, cost-effective, wide environmental conditions, high reliability, flexibility, compliance with electromagnetic interference and harmonic content, can be modified for existing applications and can be controlled by traditional Way work, etc.
Choosing the right driver for low-power LED applications is not easy and requires different factors. For example, the commercial and residential markets have different requirements for LED luminaires in terms of operating temperature, duration of use, performance, and industry standards such as Energy Star. In addition, bulb replacement applications have unique challenges, such as LED power and driver thermal limitations, limited size, and compatible dimming technology.
As far as the standards applicable to LED general illumination are concerned, there are mainly power factor correction standards required by the US "Energy Star" and the International Electrotechnical Commission's limit standard for total harmonic distortion. Among them, the "Energy Star" V1 version of the lamp standard requires LED lighting fixtures with PFC, suitable for specific products such as recessed lights, cabinet lights and table lamps, but has nothing to do with power levels. This standard requires residential applications with a power factor (PF) greater than 0.7 and commercial applications above 0.9. This standard is a voluntary standard and will be implemented in September 2011. The "Energy Star" version 1.1 integral LED bulb standard came into effect in August 2010, requiring a lamp power factor higher than 0.7 for input power above 5W.
As mentioned earlier, there are many factors to consider when choosing the right driver for low-power LED lighting applications. Among them, industry standards such as power factor are particularly important. Next, we take an example of ON Semiconductor's related products to explore how to provide high power factor in low power lighting applications.
Solutions to improve energy efficiency in low-power LED residential lighting applications
For example, for residential lighting and cabinet lights, the power is generally between 3W and 8W. Such low power applications are best suited for isolated flyback topologies. However, the traditional offline flyback power converter uses a full-wave rectifier bridge and a large capacitor in front of the switching regulator. The power utilization of this configuration or the PF of the input line waveform is low, only in the range of 0.5 to 0.6.
This will introduce PFC. If an active PFC such as the NCP1607B can be used in front of the flyback converter, it can provide PF higher than 0.98, but the component quantity and complexity are increased, and the most suitable power is much higher than the application requirements. There are many passive PFC solutions that can improve PF, but usually use more extra components, increasing cost and board space, and reducing reliability.
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