Patent ID: 7999486

Claim:
A circuit for driving at least a light emitting diode, comprising: a voltage converting circuit, for converting an input voltage to an output voltage applied to an anode of the light emitting diode, wherein the output voltage comprises a level corresponding to a reference voltage; and a reference voltage generator, for generating the reference voltage having a level corresponding to a voltage on a cathode of the light emitting diode, wherein the reference voltage generator comprises: a detection unit, for outputting the reference voltage according to the voltage on the cathode of the light emitting diode; and a pulse width tuning unit, for tuning the duty cycle of a tuning signal according to the reference voltage and a feedback voltage corresponding to the output voltage; wherein when the voltage on the cathode of the light emitting diode is higher than a threshold voltage, the voltage converting circuit lowers the output voltage according to the duty cycle of the tuning signal.