LED driver circuit

The present invention discloses an LED driver circuit, which comprises a current source for providing a source current and a negative feedback close loop circuit which is controlled by a duplicate current of the source current. The negative feedback close loop circuit comprises an operational amplifier having a negative input end and a positive input end. The negative input end is used for sensing the loaded voltage of an LED, in which any variation of the loaded voltage will result in an output variation at the output end of the operational amplifier. The output variation will finally result in a corresponding variation at the positive end, so as to keep the loaded voltage unchanged, whereby the current flowing through the LED remains unchanged and the brightness of the LED is kept stable.