From: email@example.com (Buddy)
Subject: Re: 12V computer fans run from 27 to 38V, speeding up at high temperature
Date: 22 Oct 2002 18:39:58 -0700
NNTP-Posting-Date: 23 Oct 2002 01:39:58 GMT
You could use a low-current 5V or 12V regulator for the temperature
control IC, and use the PWM output to control a switching voltage
regulator. Or you could use the PWM signal to directly chop the 3
fans in series. Some fans do not work well when the voltage is
Winfield Hill wrote in message news:...
> firstname.lastname@example.org wrote...
> > 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
> > functions.
> 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.
> - Win