Abstract
Direct AC LED drivers have advantages over conventional LED drivers in size and cost because of no need for bulky and expensive inductive components. However, none of conventional direct AC LED drivers researched so far support triode AC switch (TRIAC) compatibility at low percent flicker. This paper achieves both TRIAC dimmer compatibility and low percent flicker by correlating a phase-cut ratio to luminance and using always-on multi-arrays, respectively, without the need of a dedicated IC. The proposed LED driver consists of a phase-cut/DC converter, a switch controller, a current regulator, and three LED arrays. The experimental results based on commercial 15W LEDs show that the percent flicker of 18.6% @ 120 Hz is achieved with an efficiency of 84.7% and a power factor of 97.3% @ 120 V.
Highlights
For indoor household and commercial lighting, light emitting diodes (LEDs) are widely replacing incandescent and fluorescent lamps because of their long lifetime and high luminous efficiency [1]-[5]
LEDs without proper control circuits cannot be directly compatible with these triode AC switch (TRIAC) dimmers because LED drivers may cause visible flicker [6]
Efficiency and the number of critical components including capacitors, diodes, and switches are depending on the number of LED arrays
Summary
For indoor household and commercial lighting, light emitting diodes (LEDs) are widely replacing incandescent and fluorescent lamps because of their long lifetime and high luminous efficiency [1]-[5]. In conventional lighting systems without using LEDs, triode AC switch (TRIAC) dimmers are used for controlling luminance of resistive loads such as incandescent or halogen light bulbs. LEDs without proper control circuits cannot be directly compatible with these TRIAC dimmers because LED drivers may cause visible flicker [6]. Flicker is defined as a change in intensity of a light source caused by the fluctuations of the light source itself, power-line flicker, or incompatibility with an external dimmer. Flicker can be quantified as two different parameters: percent flicker and flicker index. The percent flicker is more generally used than the flicker index to qualify the amount of flicker. IEEE PAR1789 standard working group introduces possible health risks of higher percent flicker [7], [8]
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