Patent ID: 7141936

Claim:
A driving circuit for a light emitting diode, comprising: a first transistor having a first gate terminal, a first drain terminal and a first drain voltage at the first drain terminal; a second transistor having a second gate terminal, a second drain terminal and a second drain voltage at the second drain terminal; a balancing circuit coupled to the first and the second transistors; a high impedance load coupled to the first drain terminal and the balancing circuit, a low impedance load coupled to the second drain terminal and the balancing circuit; wherein the first and second transistors are responsive to the balancing circuit for causing the first and the second drain voltages to be substantially equal, thereby applying a current to the low impedance load substantially equal to the current applied to the high impedance load, wherein the first drain terminal is coupled to a reference current source that delivers a predetermined, but adjustable amount of current from the first drain terminal to a ground potential, and wherein the reference current source comprises at least two transistors that are directly connected to each other in series, one of the two transistors having a source terminal coupled to the first drain terminal.