Browse Prior Art Database

Precision Current Source

IP.com Disclosure Number: IPCOM000051983D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Delaporte, F: AUTHOR [+2]

Abstract

The figure illustrates a current source which serves well in applications requiring accurately controllable output current. It consists of an operational amplifier, a bipolar transistor transfer device and two current mirrors.

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Precision Current Source

The figure illustrates a current source which serves well in applications requiring accurately controllable output current. It consists of an operational amplifier, a bipolar transistor transfer device and two current mirrors.

The operational amplifier forces current I1 through resistor R to be proportional to input voltage Vin, and current mirrors T2/T3 and T4/T5 render output current Iout equal to current I1. T1's base current I2 is duplicated in the collector of T3 by current mirror T2/T3. Current I3 is fed to current mirror T4/T5 which generates current I4 equal to I3. Current I4 is fed directly into the emitter of T1 and compensates for base current I2. Therefore, current Iout is equal to I1.

It should be noted that the figure shows only the principle of the proposed current source and that its actual implementation can be further improved to meet additional requirements. For example, transistor T1 can be replaced by a Darlington circuit or compound transistor. Current mirrors can also be provided with regulation emitter resistors and sensing transistors connected to their base common node.

The whole circuit is equivalent to floating-type powering of the base-to-emitter junction of T1 so as to simulate an infinite beta gain for transistor T1.

The same circuit can be implemented with NPN transistors if the required output current has to have a direction opposite to that shown in the figure.

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