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From: LHBradley.firstname.lastname@example.org (Larry Bradley)
Subject: Re: 12V computer fans run from 27 to 38V, speeding up at high temperature
Date: Mon, 04 Nov 2002 17:22:37 GMT
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Do you really need a switcher? Couldn't you just apply a PWM voltage
to the fan to control the speed? Or would the magnitude of the 30 volt
pulses cause some grief?
Winfield Hill wrote:
>> 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
> Thanks, that's right - I'm planning on a BFC to insure any fan will
> work. BTW, I find it appealing to use standard uP heat-sink/fans.
> WRT a 5 or 12V regulator, why add additional regulators if one can
> do the job with one IC (along the lines of my circuit example)? I'm
> looking for the most viable modest parts-count solution. Right now
> I'm leaning towards an NSC LM2674 260kHz switcher IC with a say 220uH
> inductor and a small thermistor-resistor network plus a zener diode.
> - Win
Larry Bradley VE3CRX
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