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# Dual Polarity Precision Reference Voltage Supply

IP.com Disclosure Number: IPCOM000074066D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 39K

IBM

## Related People

Schultz, RA: AUTHOR

## Abstract

Circuit 10 provides respective positive and negative DC precision reference voltages +V1 and -V2 at outputs 11 and 12, respectively.

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Dual Polarity Precision Reference Voltage Supply

Circuit 10 provides respective positive and negative DC precision reference voltages +V1 and -V2 at outputs 11 and 12, respectively.

The positive reference voltage +V1 is taken across a reference zener diode 13 and resistor R1. A constant current source S regulates zener current Iz.

Source S includes a pair of operational amplifiers 14 and 15 connected back to back in a closed-loop system which uses positive feedback. It can readily be demonstrated that system stability is achieved with positive feedback as long as the total loop gain does not exceed unity, i.e. Rf/Ri<1. Amplifier 15 provides a unity gain inversion of the positive reference output +V1, thereby providing a negative reference output -V2 which is directly proportional +V1. By judiciously selecting the V-I characteristic of diode 13, the arrangement together with the use of the precision resistors Ri, Rf keeps the voltage across R1 well regulated. That is to say, large variations in the load current through loads L1 or L2 do not appreciably change the output voltages. Furthermore, no appreciable change in the zener diode bias current Iz occurs as a result of the circuit 10 supplying these load variations.

Using ideal operational amplifiers, i.e., very large open-loop gains and negligible offset voltages, the following equations describe the important parameters: (1) +V1 = R1 over Ri-Rf Vz (2) -V2 = -Ri over Ri-Rf Vz (3) Iz = R1+Rf over R1(Ri-Rf) Vz.

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