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Schmitt Trigger Circuit

IP.com Disclosure Number: IPCOM000080062D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Epley, PR: AUTHOR [+2]

Abstract

The circuit diagrammed presents a scheme for precisely and easily setting the input voltages at which the Schmitt trigger changes state. The circuit is adaptable to use as an integrated circuit for the switching voltages of the circuit as it is controlled by resistor ratios which are relatively easy to predetermine, rather than by absolute resistor values which cannot be precisely controlled.

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Schmitt Trigger Circuit

The circuit diagrammed presents a scheme for precisely and easily setting the input voltages at which the Schmitt trigger changes state. The circuit is adaptable to use as an integrated circuit for the switching voltages of the circuit as it is controlled by resistor ratios which are relatively easy to predetermine, rather than by absolute resistor values which cannot be precisely controlled.

In the circuit, a pair of transistors 1 and 2 have a common-current control 3 in their emitter circuit and have their collectors connected to a voltage source 4, transistor 1 directly and transistor 2 through a resistor 5. The base of transistor 1 is directly driven by the control voltage on terminal 6. The base of transistor 2 is connected through a resistor 7 to ground, through a resistor 8 to a voltage terminal 9 which can be a precision voltage or the regular power supply, and through a resistor 10 to the collector of a transistor 11. The collector of transistor 2 is connected through a resistor 12 to the base of transistor 11 and to a current control 13.

In operation with a low voltage on input 6, transistor 2 will be conductive and the low voltage on its collector holds transistor 11 nonconductive. As the input voltage increases, the circuit remains in the same condition until the input voltage exceeds the base voltage determined by the ratio of resistors 8 and 7, whereupon transistor 1 becomes conductive and transistor 2 turns off. The resultan...