Patent ID: 8278831

Claim:
A driver circuit for a light emitting diode, comprising: a first driver circuit for generating a first current output (I high ) for driving the light emitting diode, wherein the first driver circuit has a control switch for interrupting the supply of the first current output; a second driver circuit for generating a second current output (t low ) for driving the light emitting diode, wherein the second driver circuit has a control switch for interrupting the supply of the second current output, wherein the output of the driver circuit comprises the combination of the first and second driver circuit outputs, in the form of a pulse width modulated output current which alternates between a high current including the first current output (I high ) generated by the first driver circuit and a low current comprising the second current output (I low ) generated by the second driver circuit; wherein the high current value (I high ) comprises an LED operation current, and the low current value (I low ) comprises a non-zero measurement current; and wherein the first current output is operated with a frequency of the pulse width modulated output, and the second current output is on for the duration of a measurement cycle.