Constant current linear driver with high power factor

A controller for controlling a plurality of light-emitting diode (LED) strings that are connected in series, the controller comprising:

• an input node for receiving a rectified input AC (alternating current) voltage;
• a common current sense node for sensing current flow in the plurality of LED strings;
• a reference voltage generator configured to generate a plurality of reference voltages, the reference voltage generator further configured to vary the plurality of reference voltages based on a sampled voltage signal, the sampled voltage signal comprising one or both of a peak voltage of the rectified input AC voltage and a peak voltage of an LED diode forward voltage, wherein the reference voltage generator is configured to:
• respond to one or both of a peak voltage of the rectified input AC voltage and a peak voltage of an LED diode forward voltage;
• in response to the rectified input AC voltage, decrease each of the plurality of reference voltages when the sampled voltage signal is increased, and increase each of the plurality of reference voltages when the sampled voltage signal is decreased;
• and
• when responding to the LED diode forward voltage, increase each of the plurality of reference voltages when the sampled voltage signal is increased, and decrease each of the plurality of reference voltages when the sampled voltage signal is decreased;
• a plurality of linear regulators, each linear regulator coupled between a cathode of a corresponding LED string and a common current sense node, each linear regulator configured to control a current through the corresponding LED string based on a corresponding reference voltage;
• wherein the controller is configured to regulate a current through the plurality of LED strings to be in phase with the rectified input AC voltage and to maintain a target average LED current over changes in one or both of the rectified input AC voltage and the LED diode forward voltage.