Browse Prior Art Database

Current Supply

IP.com Disclosure Number: IPCOM000091271D
Original Publication Date: 1967-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

May, RE: AUTHOR

Abstract

A Darlington type circuit can be used as a current supply by using an operational amplifier to compensate for temperature sensitivity and required current control.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 100% of the total text.

Page 1 of 2

Current Supply

A Darlington type circuit can be used as a current supply by using an operational amplifier to compensate for temperature sensitivity and required current control.

The operational amplifier summing action forces V1A to equal V1. The current IE is negligible compared to 1 because the 10K impedance is much greater than the impedance seen looking into the emitter of the Darlington circuit. Therefore, the drop across the 10K resistor is negligible and V1B = V1A = V1. The current 1 is then equal to (V2-V1)RX.

Due to the Darlington action, the current IB is negligible so that the current to the load is equal to 1. Capacitor C prevents oscillations. The accuracy of the current supply can be made to approach 0.1% and can be made controllable by controlling the magnitude of RX.

The advantage of this circuit over the standard Darlington circuit is the output current is independent of the VBE voltages of Q1 and Q2. Therefore a change of VBE due to temperature or a replacement transistor does not affect the output current. Fixed precision resistors can be used thus eliminating the need for variable resistors.

Current can be made to flow in the opposite direction by using NPN transistors in place of PNP and reversing the polarity of V1 and V2.

1

Page 2 of 2

2

[This page contains 1 picture or other non-text object]