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Operational Indicator System for the IBM Personal Computer Fan

IP.com Disclosure Number: IPCOM000044469D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Geany, G: AUTHOR [+4]

Abstract

This article describes a specific means to ascertain, with speed and reliability, that the cooling fan is operational during the testing phase of the manufacturing cycle for the IBM Personal Computer, the specific means being a thermistor with constant current load. The system, as illustrated in the schematic diagram of the drawing, works by using the principle of the change in resistance of a thermistor when operated in the self-heating mode. Operational amplifier IC1 is used in the differential mode with one of its input terminals connected to voltage V1, derived from the main supply V+ by voltage division between resistors R1 and R2. The other input is connected to voltage V3 provided by the potential drop across resistor R5 and current flowing through field-effect transistor (FET) Q1, thermistor T and R5.

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Operational Indicator System for the IBM Personal Computer Fan

This article describes a specific means to ascertain, with speed and reliability, that the cooling fan is operational during the testing phase of the manufacturing cycle for the IBM Personal Computer, the specific means being a thermistor with constant current load. The system, as illustrated in the schematic diagram of the drawing, works by using the principle of the change in resistance of a thermistor when operated in the self-heating mode. Operational amplifier IC1 is used in the differential mode with one of its input terminals connected to voltage V1, derived from the main supply V+ by voltage division between resistors R1 and R2. The other input is connected to voltage V3 provided by the potential drop across resistor R5 and current flowing through field-effect transistor (FET) Q1, thermistor T and R5. Since the voltage across the input terminals of the operational amplifier IC1 is very small, voltage V3 differs from voltage V1 by only a few microvolts. A known constant current flows through thermistor T. By choosing the right amount of current through thermistor T, its temperature can be adjusted to a value much higher than ambient, thus allowing the air flow out of the fan from the computer to decrease the resistance of the thermistor T by a substantial amount. Operational amplifier IC1 keeps the current through thermistor T constant by varying the value of the channel resistance of FET Q1 by...