From: Winfield Hill
Subject: Re: 12V computer fans run from 27 to 38V, speeding up at high temperature
Date: 22 Oct 2002 10:03:02 -0700
Organization: Rowland Institute
X-Newsreader: Direct Read News 2.98
> Analog Devices, Maxim, micrel, NatSemi, and SMSC make ICs for this
> function. Most use an external diode junction for temperature
> sensing, the diode is built-into the CPU. Micrel has a chip that can
> take a thermistor input. Most have a PWM output for speed control
> with an external NPN or NMOS, but there are a few with analog outputs
> for Voltage-control. Some are closed-loop temperature controllers,
> some are closed-loop RPM controllers, and some are both. Their
> websites have some good apps notes for RPM vs. temperature transfer
Thanks for the list. Hmm, most assume the fan's power supply is
12V, etc. Some, like Microchip, also require 5V to run the fan-
control IC. So our spec is, up to 40V in, 12V max out, with the
speed controlled by temperature. Will any of them meet our spec?
> If you want to build your own, make sure to start the fan at full
> power for some time before slowing down. You probably should have
> a low RPM alarm mechanism. Don't run at less than 30% full speed.
> You'll find big differences between generic fans at lower voltages.
Good advice, thanks.
> Winfield Hill wrote ...
>> -Thinking kindly on the hungry masses here at s.e.d., here's a bone
>> for yo'all to knaw on. I'd like to run various generic 12V computer
>> heat-sink fans from a 27 to 38V supply, using a PWM buck regulator.
>> The fan should run slowly at room temp, but increase to full speed
>> by ~ 40C heat-sink temperature. Full speed would be 12V fan drive,
>> which shouldn't be exceeded even if the temperature rises over 40C.