DACD Solution Simplifies Smart LED Lighting Design

July 12, 2016 // By John Wiggenhorn, Fairchild Semiconductor
Smart LED lighting systems in various fields - from home to commercial to public applications – are taking off at great speed. The U.S. market researcher IHS projects over 160 Million smart lighting systems to be sold in commercial applications this year, with a CAGR of over 40 percent through 2018. This is due to their inherent advantages, such as low power consumption, dimmability and choice of color, flexibility in size and easiness of combining to form LED strips. These capabilities are key for creating attractive lighting solutions according to the customers' architectural guidelines and preferences. One frequent problem that industrial lighting designers have when they are developing smart LED solutions is not having the necessary power supply expertise, which was not a key competency before LED lighting took off.

Another difficulty for inexperienced LED lighting designers arises when systems have to be designed for various wattage levels. The complaint heard most often is that it takes lighting product designers too long to respond to different wattage specifications because each single solution tends to be customized. This implies devising different semiconductor controller circuits, along with different magnetic components. The result is that LED solutions for industrial and commercial lighting systems tend to be expensive.

The commonly used driver solution in LED lighting products is based on switched mode power supply (SMPS) technology. Although well proven and reliable, SMPS-based drivers do not offer the advantages of LED lighting engines with newer Direct AC Drive (DACD) technology.


The Flicker Problem

The DACD advantages, such as lower cost, smaller form factor, much higher performance and a longer system lifetime are compelling. Yet DACD has been slow to take off, particularly in the commercial and industrial market segments. A key reason is the issue of flicker. Flicker occurs when the AC line to supply the LED system goes through the zero crossing points of its sinusoidal trajectory at twice the powerline frequency of 100/120 Hz. This means the supply voltage momentarily drops to zero and the LEDs switch off, which sometimes causes the effect of a perceptible flicker.

Flicker is not always an issue, but it can be problematic for offices, schools, stores and other brightly lit commercial and industrial spaces, as well as for live video recordings and smartphones.


Flicker Specs and Solutions

The basic solution to the often disturbing flicker effect is to keep LEDs excited during the AC line voltage drops. This seems like an easy enough remedy. But the practical solutions can be problematic. Thus, up to now, DACD suppliers have used traditional approaches of energy storage to keep the LEDs excited. While this basically solves the flicker effect, it also causes distortion to the input line current

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