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Two-Speed Fan Control with Thermal Sensor

IP.com Disclosure Number: IPCOM000113423D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Allard, DJ: AUTHOR [+5]

Abstract

Disclosed is a method for controlling the speed of a fan used to cool a computer system between two levels in accordance with the output of precision temperature sensor located near the point where of air moved by the fan is exhausted. A reference voltage generated using a Zener diode is applied as an input to a comparator circuit and to the sensor. The output of the sensor is applied as the other input to the comparator circuit, and the output of the comparator circuit is in turn used as the input to a transistor network. The direct-current fan motor is wired to a voltage source in series with a speed control resistor, which is short circuited by the transistor network under conditions of relatively high measured temperature, applying a higher voltage to the motor,

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Two-Speed Fan Control with Thermal Sensor

      Disclosed is a method for controlling the speed of a fan used
to cool a computer system between two levels in accordance with the
output of precision temperature sensor located near the point where
of air moved by the fan is exhausted.  A reference voltage generated
using a Zener diode is applied as an input to a comparator circuit
and to the sensor.  The output of the sensor is applied as the other
input to the comparator circuit, and the output of the comparator
circuit is in turn used as the input to a transistor network.  The
direct-current fan motor is wired to a voltage source in series with
a speed control resistor, which is short circuited by the transistor
network under conditions of relatively high measured temperature,
applying a higher voltage to the motor,

      The fan is thus allowed to run at a low speed, generating a low
level of acoustical noise, when a sufficiently low air-exhaust
temperature indicates that adequate cooling is being provided.  The
fan speed is automatically increased to a higher level when a
relatively high air exhaust temperature indicates that a higher level
of cooling is required.  This type of temperature measurement is
responsive both to changes in the heat generated within the system
and to changes in the ambient temperature in which the system
operates.

      The Figure is a schematic diagram of a circuit used to power
and control a fan 10 in response to variations in air temperature
measured by a temperature sensor 12.  A reference voltage VREF of 5.1
volts is developed by passing the input voltage of 12 volts through a
dropping resistor 14 and a thermally stable zener diode 16.  This
reference voltage is applied as a supply voltage to temperature
sensor 12, which is an LM35 precision temperature reference having an
output voltage determined by the temperature measured, increasing ten
millivolts per degree Celsius.  The output voltage of sensor 12 is
applied as the posi...