When considering LED driver topologies to convert AC input voltage to a constant regulated current source for the LED loads, it is helpful to view LED applications in three general power levels: low-power applications which require less than 20W input, mid-power up to 50W; and high-power requiring higher than 50 W input. The designer faces a different mixture of challenges from cost, space, efficiency, design complexity, isolation (perhaps), power factor, and reliability, for example.
•Low-power solutions which target small lamp sizes require small design volumes to fit the LED driver, consistent light radiation by controlling the current through the LED, efficiency, and low cost. In order to be compliant with Energy Star Program Requirements for Luminaires, the light fixture must have a power factor = 0.7 for residential applications and = 0.9 for commercial applications for input power greater than 5 watts.
•Mid-power solutions still require small design volumes and power factor correction is required. Efficiency and reliability are also important design constraints in this power range.
•High-power solutions focus on the best efficiency and reliability at reasonable cost using a low BOM count.
While there are aspects of the designs which are common across all power levels—such as the need for efficiency—the way these affect the design differs. This article looks at and recommends basic topologies which are best suited to each of these three power ranges, to satisfy the design challenges.
Click to read "The challenges of choosing off-line LED-driver topologies," which originally appeared online at EETimes-Europe.
About the author
Brian Johnson is Lighting Specialist for Fairchild Semiconductor Corp.
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