Filter-free AC direct LED driver with unity power factor and low input current THD using binary segmented switched LED strings and linear current regulator

A compact LED driver with high power factor and low harmonic distortion is proposed for the AC direct LED lighting. For the compact implementation of LED lamp, all the bulky passive components such as inductors and electrolytic capacitors are eliminated. To meet power factor and total harmonic distortion regulations, the current flows through LED string is controlled by a linear current regulator. To minimize the power loss of the linear current regulator, the voltage drop of the whole LED string is adjusted by means of binary switching. The drain voltage of the linear current regulator is controlled by simple digital logics and comparators to limit the current within predefined range. The proposed LED driver was verified by simulations and a prototype experiment kit.