Patent ID: 7948455

Claim:
A device for adjusting a driving voltage provided to a plurality of light emitting diodes (LEDs), comprising: a switchable current sink coupled to cathodes of the plurality of LEDs for providing a regulated current to the plurality of LEDs, the switchable current sink being capable of providing a first reference voltage and outputting a plurality of voltage drops; a DC-DC converter coupled to anodes of the plurality of LEDs for providing the driving voltage to the plurality of LEDs; a reference circuit coupled to the switchable current sink, the reference circuit being capable of receiving the first reference voltage and the plurality of voltage drops from the switchable current sink, the reference circuit further being capable of selecting a minimum voltage drop from the plurality of voltage drops and comparing the first reference voltage with the minimum voltage drop to generate a second reference voltage for the DC-DC converter, wherein the DC-DC converter adjusting the driving voltage according to the second reference voltage to achieve the minimum voltage drop equal to the first reference voltage, the DC-DC converter further comprising: a converting unit having a voltage input terminal, a voltage output terminal, and a plurality of control terminals, the voltage input terminal receiving a DC input voltage, the voltage output terminal outputting the driving voltage, and a controller coupled to the converting unit, the controller being capable of providing a plurality of control signals to the plurality of control terminals, the plurality of control signals having a switching sequence and a switching cycle based upon the second reference voltage; a feedback circuit receiving the driving voltage from the converting unit, the feedback circuit being capable of scaling the driving voltage down to a scaled-down voltage; and a comparison circuit receiving the scaled-down voltage from the feedback circuit and further receiving the second reference voltage, the comparison circuit being capable of comparing the scaled-down voltage with the second reference voltage to get a comparison result, the comparison circuit further being capable of outputting the comparison result to the controller to start a new switching cycle.