Patent ID: 8269430

Claim:
An apparatus comprising: a plurality of light-emitting diode (LEDs), wherein each LED has an anode and a cathode; a voltage source circuit that is coupled to the anode of each LED; a current source circuit having a plurality of feed elements, wherein each feed element is coupled to the cathode of at least one of the LEDs; a first set of voltage detectors, wherein each voltage detector from the first set of voltage detectors is coupled to the cathode of at least one of the LEDs so as to compare the cathode voltage of its LED to a first reference voltage; a second set of voltage detectors, wherein each voltage detector from the second set of voltage detectors is coupled to the cathode of at least one of the LEDs so as to compare the cathode voltage of its LED to a second reference voltage, wherein the second reference voltage is less than the first reference voltage; and a voltage controller that is coupled to the voltage source circuit and to each voltage detector from the first and second sets of voltage detectors, wherein the voltage controller decreases the voltage supplied to the plurality of LEDs when each of the cathode voltages are greater than the first threshold voltage, and wherein the voltage controller decreases the voltage supplied to the plurality of LEDs when at least one of the cathode voltages is less than the second reference voltage.