Series-Based AC LED Driver with Efficiency Improved

Abstract

A dimmable AC LED driver circuit with high power factor (PF) and low total harmonic distortion (THD) is proposed, and such a circuit takes series driving based on the basic unit mainly built up by the base of the bipolar junction transistor (BJT) connected with the drain of the metal oxide-semiconductor field-effect transistor (MOSFET). Accordingly, the isolated base driver for the BJT is not required. In addition, the efficiency is further improved by adding one switchable LED block constructed by several LED strings along with individual switches. As the switch in this block is turned on, the corresponding LED string is reverse-biased, whereas as the switch in this block is turned off, the corresponding LED string is forward-biased. By doing so, the redundant input voltage across the BJT current source can be decreased, thereby reducing unexpected power dissipation and improving overall efficiency. Eventually, a prototype circuit is built up and controlled by the field programmable gate array (FPGA). By means of experimental results, the effectiveness of the proposed topology can be verified.