High impedance output current source

Details High impedance output current source High impedance output current source

1978-12-08

1980-12-02

Shoop, William M.

Electricity: power supply or regulation systems

Remote sensing

307297, 330257, G05F 156

Patent

active

042374146

ABSTRACT:
Circuit which is suitable to be manufactured in integrated circuit form for providing a constant source current at an output for driving a load. The circuit includes a reference current source for providing a reference current, and a PNP turn around circuit consisting of matched transistor devices. The output current from the circuit is provided at the collector electrode of a second one of the matched transistors. A third transistor is coupled between the second transistor and the output of the circuit in a cascode configuration to buffer the collector of the second transistor from variation in the voltage level appearing at the output of the circuit. Additionally, another transistor is coupled between the reference current source and the cascoded transistor forming therewith a Darlington amplifier which produces a high output impedance at the output of the circuit. A bias circuit is supplied between the turn around circuit and the reference current source to eliminate errors by providing the base current drive for the matched transistors of the turn around circuit and for establishing a reference potential between the base and collector electrodes of the second transistor of the turn around circuit such that the current supplied therefrom is independent to the magnitude of the voltage derived across the load to be connected to the circuitry.

REFERENCES:
patent: 3735240 (1973-05-01), Davis et al.
patent: 3843933 (1974-10-01), Ahmed
patent: 3952257 (1976-04-01), Schade, Jr.
patent: 4008441 (1977-02-01), Schade, Jr.
patent: 4045694 (1977-08-01), Ahmed

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