A 0.9 PF LED driver with small LED current ripple based on series-input digitally-controlled converter modules

This paper introduces a digitally-controlled off-line LED driver based on low-voltage series-input converter modules. The series-input connected modular architecture is adopted to utilize low-voltage high-frequency circuits and low-profile components in off-line applications. Input current is regulated to be constant using a simple controller to achieve 0.9 power factor (PF) without a traditional power factor correction (PFC) stage. Additionally, a bidirectional buck second stage is used to reduce 120 Hz current ripple in the LEDs with minimal energy storage requirements and high efficiency. Experimental results are presented for a series-input system with three modules that drive 6, 8 and 7 LEDs with less than 15% line-frequency current ripple using small filter capacitors.