Offline high power factor TRIAC dimming LED driver design

According to the International Energy Agency (IEA), 19% of the electricity consumed worldwide is used for lighting. Therefore, in recent years, countries around the world have been working to replace energy-efficient incandescent light sources with more energy-efficient solutions. With the continuous improvement of lumen output ( LED ) in lumen output and light efficiency, the average cost per lumen of light output is also decreasing, combined with the advantages of LED in high directivity, long life and low maintenance cost. LED lighting (also known as solid state lighting, or SSL) has become an extremely compelling alternative.

Energy efficiency specification requirements for solid state lighting

In order to promote energy conservation, government agencies or regulatory organizations around the world have developed different LED lighting specifications, mainly in terms of power factor (PF) requirements. For example, the European Union's International Electrotechnical Union (IEC) specifies the total harmonic distortion performance of lighting applications with power greater than 25 W, which is also applicable to other international standards in some regions.

In addition, the US Department of Energy has developed and published an "Energy Star" standard for solid-state lighting. This voluntary standard includes a range of requirements for common residential and commercial lighting fixtures (such as recessed lights, cabinet lights, and desk lamps) covering minimum lumen output, overall efficacy, reliability targets, light color temperature, and a range of other critical system level requirements. . It is worth noting that this standard does not directly include the power efficiency requirements, but includes the power factor requirement, that is, regardless of the power level, the residential application requires a PF greater than 0.7, and the commercial application requires a PF greater than 0.9, while the integrated LED lighting The requirement is that the PF is greater than 0.7.

Of course, not all countries absolutely mandate improved power factor in lighting applications, but some applications may have this requirement. For example, utilities may strongly promote the commercial use of products with high power factor in utilities. In addition, when utilities own/maintain street lights, they can decide whether they want a high power factor (usually greater than 0.95+), depending on their wishes.

13 W LED downlight design example

1. Establish maximum load design goals with reference to surrogate standards


Take the ENERGY STAR solid-state lighting standard as an example. This standard contains the overall requirements for determining the efficacy of the luminaire; in fact, this standard is a system-level standard that involves selected LEDs, field operating temperatures, optical components, and drives. Power conversion energy efficiency, etc. Lamp developers can therefore trade off LED choices, use of optical components, thermal management solutions, drive topologies, and designs to meet overall requirements. The following table lists the key system requirements for recessed lights in the Energy Star version 1.1 residential and commercial application solid state lighting specification version 1.1.

Key requirements for recessed lights for the Energy Star version 1.1 residential and commercial solid state lighting specifications

Table 1: Key requirements for recessed lights for the ENERGY STAR version 1.1 residential and commercial solid-state lighting specifications.

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