A controller for controlling a plurality of serially-connected LED strings includes a reference voltage generator configured to generate a plurality of reference voltages. The reference voltage generator is further configured to vary the plurality of reference voltages based on a sampled voltage signal. The sampled voltage signal can include one or both of a peak voltage of the rectified input AC voltage and a peak voltage of an LED diode forward voltage Vf. The controller further includes a plurality of linear regulators, each linear regulator coupled between a cathode of a corresponding LED string and a common current sense node, and each linear regulator is configured to regulate a current through a corresponding LED string according to a corresponding reference voltage.