Patent ID: 7714520

Claim:
An LED driver circuit comprising: a power controller having an input end connected to a power source and a reference voltage; a voltage regulator connected to a voltage output end of the power controller; a detecting resistor connected to an output end of the voltage regulator for receiving an output current of the voltage regulator; a light emitting device formed by at least one LED and serially connected to the detecting resistor and one end the light emitting device being grounded; and a voltage detecting circuit having a first input end connected to a high potential end of the detecting resistor and a second input end connected to another end of the detecting resistor; the output end of the voltage detecting circuit being connected to a feedback end of the power controller so as to output a detecting voltage signal to the power controller; the power controller adjusting the output voltage according to the voltage difference between the detecting voltage signal and the reference voltage so as to output a stable current with a predetermined value to the light emitting device; and wherein the voltage detecting circuit is a differential amplifier; and wherein the differential amplifier has the first input end, the second input end, and the detecting voltage signal output end; the differential amplifier further includes resistors R 1 , R 2 , R 3 , and R 4 ; the first input end of the differential amplifier is serially connected with the resistor R 3 and then connects to the high potential end of the detecting resistor, and one end of the resistor R 4 is connected between the first input end of the differential amplifier and the resistor R 3 and is grounded with another end; the second input end of the differential amplifier is serially connected with the resistor R 1 and then connects to the lower potential end of the detecting resistor, and the resistor R 2 is connected between the second input end of the differential amplifier and the output end of the differential amplifier; and the output end of the differential amplifier is the output end of the voltage detecting circuit.