The traditional engine used in most LED lighting products combines LEDs with Switched Mode Power Supply (SMPS) technology and though well proven, SMPS-based engines do not offer the advantages of LED lighting engines using newer Direct AC Drive (DACD) technology.
Though these advantages – lower cost, smaller form factor, much higher performance and a longer system lifetime – are compelling, DACD has been slow to take off, particularly in the commercial and industrial market segments.
A key reason that lighting manufacturers haven’t fully embraced DACD is the inherent issue of flicker, which happens when LEDs very briefly shut off. When the AC line goes across the zero crossing point and the voltage drops to zero, the LEDs switch off or flicker.
Though flicker is not always obvious, it can still cause headaches for a small percentage of people exposed to flickering lights for long periods. This is a major issue for offices, schools, stores and other brightly lit commercial and industrial spaces where people spend a lot of time.
While there are currently no official standards governing flicker, most manufacturers and customers accept the US Energy Star recommended spec for calculating flicker index, which suggests a figure of 0.15 or lower is optimal. Anything below 0.15 is considered imperceptible so, naturally, lighting manufacturers aim to achieve or surpass this.
In addition to requiring that lights have an acceptable flicker index, customers will often conduct a simple test to ensure the lights work properly. They take photos of the lights with their smartphones and if black lines appear in the images, they know that the flicker level is too high and consequently will not accept them.
Illustration of high flicker index (left) vs low flicker index (right)
The obvious solution to flicker is to keep LEDs excited when the power drops, which seems like an easy remedy but in practice is problematic. To date, other DACD suppliers have used traditional approaches for energy storage to keep the LEDs excited. While this solves flicker, it also causes distortion to the input line current waveform, which impacts the Power Factor (PF) and Total Harmonic Distortion (THD) performance.
This is a particular problem for industrial and commercial lighting products, which must meet widely accepted guidelines for PF and THD performance or be rejected by the customer. To comply with the specs, the PF must be 0.9 or greater while THD typically needs to be less than 20 percent.
Fortunately for manufacturers, Fairchild is helping solve these issues with our new family of DACD solutions, which overcome flicker while maintaining a high PF and a low THD. The new DACD solutions accomplish this using our proprietary solution, which supplies the current necessary to keep the LEDs excited while simultaneously maintaining the sinusoidal waveform of the input current so no distortion is created to impact PF and THD performance.
Manufacturers can take advantage of our new family of DACD solutions and develop new DACD-based LED lighting products that can command higher margins in the more lucrative commercial and industrial lighting markets.
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