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Method for Controlling Fan Speed Using 5 Volt to 12 Volt Pulse Width Modulation

IP.com Disclosure Number: IPCOM000008491D
Publication Date: 2002-Jun-17
Document File: 3 page(s) / 78K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for controlling the speed of fans used to cool computer motherboards. Benefits include reduced noise and smoother fan operation.

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Method for Controlling Fan Speed Using 5 Volt to 12 Volt Pulse Width Modulation

Disclosed is a method for controlling the speed of fans used to cool computer motherboards. Benefits include reduced noise and smoother fan operation.

Background

Currently, when the volt signal to a fan is too low, the fan shuts off and the tachometer function inside the fan ceases to work. This prevents devices that measure fan speed from working when the fan is running below full speed.

General Description

The disclosed method controls the pulse width of a ~30 Hz, 12 volt signal to a 12 volt fan in order to adjust fan speed. By not completely turning off the fan between pulses, the disclosed method keeps the tachometer circuitry inside the fan energized, so that devices that measure fan speed can function accurately. In addition, the fan runs more smoothly at lower speeds.

Since ~5 volts is required to turn the tachometer circuitry inside the fan on, the fan continues to rotate, making it impossible to turn the fan off. However, by adding a 5V enable line to the fan drive circuitry, it is possible to disable the 5 volt signal to the fan, allowing the fan to be completely turned off. The device controlling the speed of the fan will therefore need to have an additional signal to control each fan.

Advantages

The following are advantages of the disclosed method:

§         Reducing the noise the system produces

§         Allowing fans to run more smoothly at lower speeds

Inputs and output of fan drive

Fan drive sig...