Patent ID: 8742689

Claim:
A light emitting diode driving apparatus, suitable to drive at least a light emitting diode string; the light emitting diode driving apparatus comprising: a first operational amplifier, having a positive input terminal receiving a predetermined voltage related to a current flowing through the light emitting diode string; a first resistor, having a first end coupled to a negative input terminal of the first operational amplifier and a second end coupled to a ground; a power transistor, having a gate coupled to an output terminal of the first operational amplifier, a drain coupled to a cathode of the light emitting diode string and a source coupled to the first end of the first resistor; an error amplifier, having a first input terminal coupled to the gate of the power transistor, a second input terminal receiving a reference voltage and an output terminal outputting a control voltage; a power conversion stage, coupled between the output terminal of the error amplifier and an anode of the light emitting diode string, for providing a DC voltage to the anode of the light emitting diode string according to a level of the control voltage; a second operational amplifier, having a negative input terminal receiving a bandgap voltage; a first transistor, having a gate coupled to an output terminal of the second operational amplifier, a source coupled to a system voltage and a drain coupled to a positive input terminal of the second operational amplifier; a second resistor, having a first end coupled to the positive input terminal of the second operational amplifier and a second end coupled to the ground; a second transistor, having a gate coupled to an output terminal of the second operational amplifier, a source coupled to the system voltage and a drain producing the predetermined voltage; and a third resistor, having a first end coupled to the drain of the second transistor and a second end coupled to the ground.