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banditpowdercoat
03/04/2010, 09:01 PM
I am building a fan/temp speed control using a 10K thermistor, 10K Pot and Mosfet. All works fine, but I would like more gain, I guess it is out of the thermistor. I have looked and I don;t think I can find one that will work directly. Basically, I would like the Mosfet to be triggered with the 20*f change but at 10* change, or there abouts. If that makes sense.
Faster slope I guess it is.
This picture is somewhat what I am building. But change the Switch for a 10K Thermistor, and the Resistor for a 10K Pot
The reason for the pot is to be able to adjust the "on" signal for different brushless fan's.
http://upload.wikimedia.org/wikipedia/en/4/4a/Mosfet_n-ch_circuit.svg

Is there something easy I can incorporate? I thought about an OP Amp, but maybe simpler design? a transistor for a darlington configuration maybe??

banditpowdercoat
03/04/2010, 09:05 PM
Trying to upload a pic from wikipedia. Not seeming to work. Hopefully this link works

http://upload.wikimedia.org/wikipedia/en/4/4a/Mosfet_n-ch_circuit.svg

stugray
03/04/2010, 11:01 PM
That pic is for a MOSFET switch LED driver.

I would need to see a schematic of your setup to help.

Stu

banditpowdercoat
03/04/2010, 11:15 PM
Like I said in my first post, I don;t have a schematic on my computer. but take that schematic, swap the Switch for a Thermistor, and the Resistor for a 10K Pot, just use 2 of the pot leads for a variable resistor. The schmatic is the same. Run a fan or LED, doesn't matter. Higher the temp, the faster the fan or brighter the light.

heres a drawing where I got the idea

http://www.heatsink-guide.com/control.gif

banditpowdercoat
03/05/2010, 12:59 PM
Would an Op-Amp give me more gain from the Thermistor to the Mosfet? basically, The Thermistor is 9.7K @ 80F and 8.36K @ 90F I would like to drive the Mosfet from 0 to close to 100% in that change from the thermistor. I'll try draw up a schematic, just found a prog can do that with.

banditpowdercoat
03/05/2010, 01:29 PM
Here is schematic now.
Any and all help appreciated. I have basic electronic knowledge, but when getting into the fancier stuff, I don't know much.