Patent ID: 8907583

Claim:
A light emitting diode (LED) driving device for driving a number (M) of LED units coupled in series, each of the LED units having an input end and an output end, said LED driving device comprising: a rectifying circuit adapted to be coupled between an alternating current (AC) power source and the input end of a first one of the LED units for receiving an AC input voltage from the AC power source, said rectifying circuit rectifying the AC input voltage to a direct current (DC) voltage; a number (M−1) of first switching circuits, each of which is adapted to be coupled between the output end of a corresponding one of first to (M−1) th ones of the LED units and ground; a second switching circuit adapted to be coupled between the output end of an M th one of the LED units and ground; and a resistor unit coupled among said first switching circuits, said second switching circuit and ground; wherein, when the DC voltage from said rectifying circuit is sufficient to turn on the first to k th ones of the LED units, in which k is a positive integer ranging from 1 to M, the output end of a k th one of the LED units is coupled to ground through first and second conductive paths, which are provided by a k th one of said first switching circuits and said resistor unit if 1≦k≦M−1, or by said second switching circuit and said resistor unit if k=M, and the output end of each of first to (k−1) th ones of the LED units is coupled to ground through a third conductive path, which is provided by a corresponding one of first to (k−1) th ones of said first switching circuits, and said resistor unit if 2≦k≦M.