I have a wonderful fan controller circuit!
Here you go:
<
http://i46.tinypic.com/2nss26a.gif>
Of course you do not need the voltage regualtor part if you have a
stable DC supply there already. I needed this to operate from a AC
transformer with unstable output.
This circuit is in my two Farnell power supplies (ex military, MASSIVE
fans). They are stopped now most of the time, only when I draw some
power they speed right up. R2 stops the fan speed from oscillating up
and down.
I have also put this circuit in a electronic DC load, it is so sweet
to have it absolutely quiet at no load and speed right up when you put
a few hundred watts into it.
Thinking about it, this circuit may well be the most beautiful I ever
made, just because it is so darn simple and really works perfectly.
_______
As you can see it uses the same idea as the temperature controller for
the laminator, just with a mosfet.
ST
On Thu, Dec 24, 2009 at 6:54 PM, Lez <lez.briddon@...> wrote:
> 2009/12/24 saposoft <sapoliste@...>:
>> Well Well this is fantastic ... care to share the schematic ?
>>
>> --- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>>>
>>> I used a thermistor, and a BC547 transisor in place of the ua741.
>>> ICs are way too expensive to waste on a thermostat ;-)
>
> I need to keep a heatsink, its about 3 inches by 2 inches, in a switch
> mode psu, cool, about 35degC would be fine, I have a fan that easily
> manages the task, but is noisy if on all the time, so was thinking of
> driving the fan via a thermostat circuit so I designed one but havnt
> built it yet, and before you say thats a waste of a 741, mine is based
> on a 18f2550 !
>
> Why, because I can understand the thing, I can use the a/d converter
> to read the thermistor, then get the controller to output PWM to
> control the fan speed, I'd never get it working if i went with analog
> electronics now!
>
> I'm ashamed to admit i've probably forgotton so much analog that i
> know less of it now than when i first got interested in my teens.
>
>
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