US 4,399,399 AGranted

Precision current source

AssigneeMotorola, Inc.

InventorEric D. Joseph

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Abstract

A circuit for providing an output current the magnitude of which is substantially independent to variations in the power supply voltage applied thereto. The circuit comprises first and second current sourcing transistors, and a conventional .DELTA.V.sub.be /R current mirror circuit for setting the current sourced from the two transistors. At least one output transistor having its base and emitter electrodes coupled in parallel with the base and emitter electrodes of the two transistors is included for sourcing the output current. An operational amplifier having its inverting and non-inverting inputs connected with respective collectors of the two transistors and its output connected to the commonly connected bases of the two transistors and the output transistor is provided which maintains the collectors of the two transistors at equal potential levels even though the magnitude of the power supply voltage may vary so that the current produced at the collector of the output transistor does not vary substantially.

Claims5

Dependent claims

A low voltage precision current source for supplying a current of predetermined value at an output the magnitude of which is substantially independent to ripple variations of a source of operating potential supplied thereto, comprising:

first and second transistors each having first, second and control electrodes, said first electrodes of said first and second transistors being adapted to receive the operating potential;
at least one output transistor having first, second and control electrodes, said first electrode being coupled to said first electrodes of said first and second transistors, said second electrode being coupled to the output of the current source, said control electrode being coupled at a circuit node to said control electrodes of said first and second transistors;
feedback circuit means coupled between said second electrodes of said first and second transistors and said circuit node for maintaining said second electrodes of said first and second transistors at substantially equal voltage potentials independent to ripple variations in the operating potential;
and
current mirror means coupled to said second electrodes of said first and second transistors for establishing a difference potential which is substantially independent of the voltage potentials appearing at said second electrodes of said first and second transistors, said current mirror means including resistive means across which said difference potential is established and through which a current is produced that is independent to variations in the operating potential, the current supplied at the output of the current source being proportional to said current established through said resistive means.

2 more elements

Dependencies are inferred from the claim text.