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Kirby Smith

Fan Control - Have your cake and ....

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DFI Fans:

 

There have been postings recommending that fans not be connected to the motherboard headers. There have also been postings about the CPU fan not starting, as I have observed myself. The forum recommendation is to connect the fans to an external fan controller or directly to the PSU.

 

Yet, one might want to utilize the motherboard's ability to measure the temperature of the relevant parts, and demand more fan output when needed. External fan controllers tend to have a single speed setting.

 

The desired properties are"

- Fan should have a minimum voltage to ensure starting

- Fan rpm should still be sensible by the motherboard

- Fan voltage should not be less than the motherboard fan controller requests based on component temperature

 

To accommodate these requirements, I assembled the circuit shown in the figure below. It is merely one of myriad ways of accomplishing the goals.

 

The circuit passes the rpm signal to the motherboard, provides my desired minimum fan voltage of 7.4 volts (the zener diode voltage + 0.6V), and it tracks the motherboard commanded voltage + 0.6V. Maximum output voltage is 10.5 volts with 12 Vdc input. I don't know what the maximum is that the motherboard commands. Unless it uses an elegant circuit, such as used in rail-to-rail op amps, it too will not reach the 12 Vdc rail, and hence would never power the fan to its maximum voltage, so I doubt I have lost much there.

 

I suspect all the parts in the diagram are available in some form from Radio Shack; I used Digi-Key for whatever I couldn't scrounge from my ancient stockpile of parts. Two of the circuits were built on Vectorboard, one for the CPU fan and one for a fan I have in the case aimed at the motherboard voltage converter fins.

 

The circuit has run for a week now, uneventfully, but is not yet tested for long-term full power loads. It does, however, have plenty of margin for any likely fans. If you have one that requires an ampere of current at 7.4 volts, the heat sink and/or air flow will have to be appropriate for 4.6W.

 

kirby

 

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Very cool. Looks like a patent is in order, then find you some company in China to build them en-mass for $1.25 a piece and resell them all over the world for $19.95. You'll be rich :)

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Thanks, but no thanks. I'm old school. I still believe that if the method is obvious to someone skilled in the art it shouldn't be awarded a patent. Not that this stops the modern Patent Office. The new theory is that anything can be patented, no matter how trivial. Let any conflict be fought out in court, and may the company with the biggest wallet win. In the meantime, both parties have to keep shoveling money at the Patent Office to maintain their patents.

 

Maybe someone will copy it and OC'ers will gain the advantage of mass production. Those skilled in this art could probably reproduce it sooner than I could write the disclosure. :D

 

kirby

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