Patent ID: 7781983
Filing Date: 2010-08-24
Classification: H05B,Y02B

Abstract:
1. A circuit for driving an LED, the circuit comprising: a current source providing a source current; a negative feedback closed-loop circuit, controlled by a replica current of the source current, including an op-amp, a capacitor, a resistor, and a pair of transistors, wherein a (−) input of the op-amp is coupled to a voltage across the LED, any change in the voltage causes a change in an output of the op-amp that in return causes a corresponding change in a (+) input of the op-amp such that the voltage is maintained unchanged, the output of the op-amp is directly coupled to the capacitor that is charged and discharged via the resistor connected thereto to stabilize a supply voltage being applied on the pair of transistors, thus a current going through the LED remains unchanged, leading to a stable brightness of the LED, and wherein the resistor is connected to a common node of the pair of transistors.