Multi-stage LED driver with current proportional to rectified input voltage and low distortion

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 a 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 based on the feedback voltages.

An apparatus comprising:

• a plurality of LED groups connected in series to form an LED string that has an first node, a last node, and one or more intermediate nodes;
• means for regulating current flows from the first, last, and intermediate nodes to an output terminal, wherein the current flows from the first, last, and intermediate nodes are regulated based on a plurality of feedback voltages;
• an output resistor that generates an output voltage at the output terminal based on the regulated current flows;
• and
• means for generating the feedback voltages from the output voltage, wherein when a selected amount of current is regulated to flow from a selected node to the output terminal, the feedback voltages cause the means for regulating to prevent current from flowing from upstream nodes to the output terminal.

An Light Emitting Diode (LED) driver circuit comprising:

• a first terminal adapted to be coupled to a first node N1 of an LED string;
• a second terminal adapted to be coupled to a second node N2 of the LED string;
• a third terminal adapted to be coupled to a third node N3 of the LED string;
• a fourth terminal adapted to be coupled to a fourth node N4 of the LED string;
• a first current cell coupled between the first terminal and a first lead of an output resistor ROUT;
• a second current cell coupled between the second terminal and the first lead of the output resistor ROUT;
• a third current cell coupled between the third terminal and the first lead of the output resistor ROUT;
• a fourth current cell coupled between the fourth terminal and the first lead of the output resistor ROUT;
• and
• a feedback circuit that supplies a first feedback voltage FBV1 to the first current cell, a second feedback voltage FBV2 to the second current cell, a third feedback voltage FBV3 to the third current cell, and a fourth feedback voltage FBV4 to the fourth current cell, wherein each of the first feedback voltage FBV1, second feedback voltage FBV2, third feedback voltage FBV3, and fourth feedback voltage FBV4 is generated from a voltage generated by the output resistor ROUT.