Browse Prior Art Database

Two Speed Fan Control Using Current Sense

IP.com Disclosure Number: IPCOM000106929D
Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Allard, DJ: AUTHOR [+2]

Abstract

This article describes a circuit arrangement for use in a personal computer (PC) system which controls the speed of a fan at a predetermined high and low speed by sensing a +5 V load on the power supply.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 65% of the total text.

Two Speed Fan Control Using Current Sense

       This article describes a circuit arrangement for use in a
personal computer (PC) system which controls the speed of a fan at a
predetermined high and low speed by sensing a +5 V load on the power
supply.

      There is a conflict between designing a system unit for the
worst-case configuration and thermal environment vs. typical
configurations and the office environment.  The result is that the
worst case is designed for and causes the typical user to be
irritated by the high acoustic noise.

      Existing solutions to the problem include fans with two speeds
that can be controlled with digital inputs and fans which
continuously monitor temperatures and adjust their speeds
accordingly.  Since reliable operation can be achieved with lower
acoustic levels on the majority of systems, a two speed fan approach
dependent on the +5 V planar load is disclosed herein.

      The circuit of this disclosure is shown in the figure. The
current level of the +5 V output to the planar is sensed through R1
(over-current sense resistor).  The high-speed trip level is set with
the value of R4.  If that current exceeds the power level that cannot
be reliably cooled with the lower fan speed, field-effect transistor
(FET) Q1 is turned on, bypassing the resistor R7 in series with the
fan. Hysteresis resistor R5 is provided on the current trip level to
prevent speed changes due to software-controlled load changes.

     ...