Patent ID: 8487549

Claim:
A light-emitting diode (LED) control circuit to adjust brightness of a lighting equipment, the lighting equipment comprising N groups of LEDs connected in series, the LED control circuit comprising: a switch comprising a first terminal, connected to a first direct current (DC) power supply, and a second terminal; a control signal generating circuit comprising an input terminal connected to the second terminal of the switch, and N output terminals, N being an integer greater than 1; a voltage conversion device connected to the second terminal of the switch, wherein the voltage conversion device converts the first DC power supply to a second DC power supply for supplying power to the control signal generating circuit; and N switching circuits, wherein a first terminal of each switching circuit is connected to the first DC power supply, a second terminal of each switching circuit is connected to a corresponding output terminal of the control signal generating circuit, a third terminal of each switching circuit is grounded, the first terminal of the Nth switching circuit is connected to a last terminal of the Nth group of LEDs, the first terminal of each of the remaining N−1 switching circuits is connected to a corresponding node between two adjacent groups of LEDs, the control signal generating circuit outputs different control signals according to the switch to turn on or off the N switching circuits, thus to supply power to the corresponding groups of LEDs; wherein the control signal generating circuit comprises a first field effect transistor (FET), an adding counter, and a 2-to-N line single bit decoder, a gate of the first FET is grounded through a first resistor, the gate of the first FET is further connected to the second terminal of the switch through a second resistor, a source of the first FET is grounded, a drain of the first FET is connected to the second DC power supply through a third resistor, the drain of the first FET is further connected to an input terminal of the adding counter, first and second output terminals of the adding counter are connected to two input terminals of the 2-to-N line single bit decoder, N output terminals of the 2-to-N line single bit decoder function as the N output terminals of the control signal generating circuit and are connected to the N switching circuits respectively, when the input terminal of the adding counter receives a signal on a rising edge for one time, a two-bit code output from the first and second output terminals of the adding counter adds one, the 2-to-N line single bit decoder converts the two-bit code to an N-bit code.