Current source circuit with constant output
 A current source circuit providing a constant output for wide variations in supply voltages is achieved by creating a constant reference current by reflecting the difference in the base to emitter voltage of two bipolar transistors across a resistor. A first current mirror creates an equal current which flows through two diode connected transistors that produce an output voltage proportional to the current flowing through them. This current also flows through a second current mirror which creates an equal current to flow to a feedback connection. The feedback connection adjusts the base voltage of the two bipolar transistors until a current equal to the reference current flows in a third current mirror. The current flowing in this third current mirror is also applied to the feedback connection to insure that all currents remain equal thereby insuring the output remains constant. 
Motorola, Inc.
G
G05F
inventional
Alan L. Roger A.
Westwick Whatley