Patent ID: 7902762

Claim:
A system for driving a light-emitting diode (LED), comprising: a constant-current mode circuit for providing a constant current to the LED; a constant-voltage mode circuit for providing a constant voltage to the LED; and a switch for switching between the constant-current mode circuit and the constant-voltage mode circuit to assert constant-current mode and constant-voltage mode respectively; wherein the constant-current mode circuit comprises: a current sensing resistor connected in series to a cathode electrode of the LED; and an error comparator coupled to receive a predetermined reference voltage and a voltage across the current sensing resistor; wherein the constant-voltage mode circuit comprises: a voltage divider connected between an anode electrode of the LED and ground; means for acquiring dividing voltage of the voltage divider; means for deriving forward voltage of the LED; a bypassing transistor coupled between the cathode electrode of the LED and the ground; and means for changing the reference voltage of the error comparator to a new reference voltage according to the dividing voltage, such that forward voltage of the LED is maintained at the derived forward voltage.