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Voltage Comparator With Adjustable Trip Point and Hysteresis

IP.com Disclosure Number: IPCOM000085420D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Beistle, RG: AUTHOR [+2]

Abstract

The device as depicted schematically shows a voltage comparator with controlled and adjustable hysteresis.

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Voltage Comparator With Adjustable Trip Point and Hysteresis

The device as depicted schematically shows a voltage comparator with controlled and adjustable hysteresis.

In operation, the input on terminal 10 is more positive than threshold. Adjustable current source 12 is set to some desired value. Under these conditions input b to the current switch 16 will cause the current at input c to be passed to ground via connection d. Output pin a is an open circuit and has no effect on the threshold voltage.

Assume that the input on terminal 10 falls below the threshold voltage. As a result the output of voltage comparator 14 will change state. The state change will change current switch 16 so that the output of adjustable current source 12 will be passed through and appear at output a.

The current from output a will flow through resistor R1 toward the wiper of the threshold adjustment potentiometer. This will cause the voltage which appears at the positive terminal of voltage comparator 14 to be driven more positive by an amount equal to the adjustable current source 12 times R1. Due to the fact that the impedance looking into the wiper of the threshold potentiometer is made at least 2 orders of magnitude less than the resistance of R1, it does not contribute appreciably to the change in threshold voltage.

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