1. A method comprising:receiving a rectified AC input signal at an input node of an LED string formed by a plurality of LED groups having interconnecting nodes and a last node that are connected to a plurality of current cells;
enabling a selected current cell based on the input signal, wherein the selected current cell regulates current flowing from a selected node to an output resistor;
generating feedback voltages based on an output voltage generated by the output resistor; and
disabling current cells that are upstream from the selected current cell.