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Driving LEDs for Easier Adoption
by James Lee - 2018-07-11 11:39:16.0

LED lighting is increasingly prominent and important in a wide range of end applications. This trend is set to continue and accelerate due to the low power, low cost and small size requirements of the latest end applications. Retrofitting incandescent installations with much more flexible and versatile LED lighting will also continue to be a significant driver of future growth.

Despite all the pluses associated with LED lighting, there are challenges to overcome. The main drawback to current solid state lighting solutions is not the LEDs themselves, but the power supplies that provide the energy to illuminate them.

Until recently, switched mode power supplies (SMPS) have been used to provide the power, but these have had longevity and lifetimeissues and are bulky, causing installation issues and necessitating mounting on separate boards with resulting interconnections and leads that are another potential source of failure. In addition, SMPS that contain active cooling devices such as fans, are particularly susceptible to early failure. They also represent significant sources of Electro-Magnetic Interference (EMI).

Recent advances in power technologies and topologies have included the advent of Direct AC Drive (DACD) power solutions. This newer approach can eliminate the traditional SMPS entirely, bringing multiple benefits in terms of cost, size, longevity and reliability. Devices such as ON Semiconductor's NCL30170, Direct AC Drive LED Driver for Power Factor Correction and Precise Constant Current Regulation are helping direct AC approaches deliver the all-round performance demanded of LED lighting applications in a number of end market sectors.

DACD topologies for LED drives typically fall into one of two arrangements – shunt or bypass - each has its strengths and weaknesses. Shunt types are easily scalable and tend to use a single IC which is good for the BoM, however, thermal performance can be an issue. In contrast, bypass topologies use multiple ICs, that while adding complexity to the BoM, can be better suited to applications with many LED strings. An Achilles heel can be that scalability is limited.

Overall, and certainly compared to SMPS, DACD is a big step forward in driving LEDs, but there is plenty of room and opportunity for improvement in the technology;

The NCL30170 is delivering on the potential for improvement. The devices use the shunt topology with all the benefits that approach brings, while at the same time allowing multiple LED strings to be connected. The result is that power can be scaled from 10W up to 200W with the total number of LED strings connected and external switches only limited by the maximum upper power level.

With dimming being a ‘must have’ for many applications to use or convert to LEDs, the capability of devices such as the NCL30170 to support analog dimming to 5% is valuable and provides the breadth of performance needed. In many retrofit applications, Pulse width modulation (PWM) dimming, often known as Phase-Cut dimming, is needed and again the NCL30170 performs well here.

Learn more about the NCL30170 design tips.

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