Patent ID: 8587217

Claim:
An apparatus for controlling multiple, series coupled light emitting diodes (LEDs), the apparatus comprising: a first LED driver to generate: a first switch control signal to control a duty cycle of a first switch coupled in parallel across at least a first LED; and a second switch control signal to control a duty cycle of a second switch coupled to at least a second LED to vary a relative intensity of the first and second LEDs, wherein the first LED is coupled in series with the second LED; a buck-type constant current source coupled to the first switch to provide a bias current for the first and second LEDs, wherein the buck-type constant current source includes an inductor and further includes a voltage source coupling switch to receive a control signal from a current controller to control coupling of an input voltage source to the inductor; and a second LED driver to generate: a third switch control signal to control a duty cycle of a third switch coupled in parallel across at least a third LED; and a fourth switch control signal to control a duty cycle of a fourth switch coupled to at least a fourth LED to vary a relative intensity of the third and fourth LEDs, wherein the third LED is coupled in series with the fourth LED.