Patent ID: 8194008

Claim:
A light-emitting device comprising: a constant current source including an amplifier, a variable resistor and a bipolar transistor, wherein an output of the amplifier is electrically connected to an input of the bipolar transistor, and a first terminal of the bipolar transistor is electrically connected to the variable resistor and an inverted input terminal of the amplifier; a buffer amplifier; an adding circuit including an input and an output, wherein the input is electrically connected to an output of the buffer amplifier; a first monitoring light emitting element including a pair of electrodes, wherein one of the pair of electrodes is electrically connected to a second terminal of the amplifier and a non-inverted input terminal of the buffer amplifier; and a second light emitting element including a pair of electrodes, wherein one of the pair of electrodes is electrically connected to an output of the adding circuit.