Patent ID: 8384311

Claim:
A Light Emitting Diode (LED) selection circuit comprising: a rectifier converting an input Alternating Current (AC) line voltage to a pulsating Direct Current (DC) voltage; multiple LED strings; multiple current sources, each current source comprising an error amplifier having a first input end, a second input end and an output end; and a transistor having a drain, a source and a gate, the drain of the transistor being connected to a bottom side of the corresponding LED string, the source of the transistor being connected to the second input end of the error amplifier and one end of a current sensing resistor, the gate of the transistor being connected to the output end of the error amplifier, wherein another end of the current sensing resistor is connected to the rectifier; and a controller being connected to the rectifier and the current sources and turning ON and OFF the corresponding LED strings, wherein the controller synchronizes frequencies of the pulsating DC voltage and generates multiple reference voltages to the corresponding current sources at an appropriate time.