A topology study of single-phase offline AC/DC converters for high brightness white LED lighting with power factor pre-regulation and brightness dimmable

Due to the recent advancement in the light emitting diode (LED) technology, high brightness white LED becomes feasible in residential, industry and commercial applications to replace the incandescent bulbs, halogen bulbs, and even compact fluorescent light bulbs. In these offline applications, high power factor, and low harmonics are of primary importance. Single stage power factor pre-regulation technology is preferred in these cost sensitive applications where power factor regulation is mandatory, while adding additional power factor correction controller will surely increase the cost. In this paper, we exam several single stage offline ac/dc power converters with power factor pre-regulation for LED lighting applications, including boost converter, SEPIC converter, flyback converter, and half-bridge converter. A boost converter is suitable for high efficiency, large LED string applications. A SEPIC converter has the best power factor correction performance, but the efficiency is not comparable with the other solutions. Flyback converter is the most commonly used topology for low power offline applications. For medium power applications, symmetrical and asymmetrical half bridge converters can be used with better power factor and high efficiency. The harmonics of the input line current is reduced and power factor is high if the current in the input inductor is discontinuous and the converter is driven with constant duty ratio. A current feedback loop can be used to control the LED brightness. The performance of these converters will be analyzed and compared in terms of power factor, efficiency, etc, based on the lab prototype boards.