LED lighting systems, LED controllers and LED control methods for a string of LEDs

摘要

LED controllers, LED lighting systems and control methods capable of providing an average luminance intensity independent from the variation of an AC voltage. A string of LEDs are divided into LED groups electrically connected in series between a power source and a ground. A LED controller has path switches, each for coupling a corresponding LED group to the ground. A management center controls the path switches, for making an input current from the power source to the string substantially approach a target value. A line waveform sensor coupled to the power source holds a representative signal during a cycle time of the power source. The representative signal is in response to an attribute of the power source, and substantially determines the target value.