So I'm building a small DC powered fan circuit for my mic preamp, since the preamp overheats if there is no air blowing across the heat sink. My problem is that the resistor I put in line to resist some of the volts from my 9volt battery is getting wayyy to hot. I have no idea if it will burn the resistor or the fan.

The fan is a laptop fan out of my Asus, it's DC at 5 volts, at .4 amps. So, ohms law tells me that I need at least a 10 ohm resistor in line at all times to knock the 9 volts down to 5 volts, at the same amperage. Then I put a 1k pot in line with it to control the speed of the fan, works brilliantly, bit sensitive, but that resistor is getting really dang hot.

How could I get around this problem? How do I reduce 9 volts to 5 volts DC safely without having to worry about burning up the resistor or the pot? Do I need a higher wattage resistor?
Quote by LeviMan_2001
One of these http://www.amazon.com/7805-5V-Voltage-Regulator-TO-220/dp/B0002ZPXJ6 you can probably find one at radio shack too.

How would I incorporate that transistor into a circuit that would work? Consider I only know basic electrical.
SMPS, that's how.
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Quote by Anonden
You CAN play anything with anything....but some guitars sound right for some things, and not for others. Single coils sound retarded for metal, though those who are apeshit about harpsichord probably beg to differ.
you need a 3 watt resistor there.

i'm surprised that 1/4th hasn't blown up yet.
Prs se Holcomb is the answer
Quote by AcousticMirror
you need a 3 watt resistor there.

i'm surprised that 1/4th hasn't blown up yet.

I am too, its a metal film one, and it gets really friken hot when it's going full blast.

I have a adjustable voltage regulator, TL783C, adjusts from 1.25 to 125 volts...it's just trying to understand how the heck to make it run 5 volts from a 9 volt source that has me stumped.
Thanks. Not really, it's an adjustable voltage regulate, letting you regulate anywhere between 1.25 to 125 volts, so depending on the resistor values you choose, it'll dictate how much voltage it'll allow through. It's rather simple, depending on the transistor, you'll have a input, output, and your adjustable. You bridge a 82 ohm across the output and adjustable pins, have your input voltage(source voltage) coming into the input pin, run the output to your load, and run your adjustable to ground, with another resistor in line with the adjustable and ground.

The resistor that's inbetween the adjustable pin and ground is what controls your voltage regulation. So depending on it's value, it'll change your voltage. The equation I used was

Output voltage=Source voltage(1+(R2/R1)) R1 and R2 being resistor 1 and resistor 2, resistor 2 being your 82 ohm resistor, and R1 being your adjustable resistor.

Heres what the finished product looks like, running a test now, and it seems to be working like planned, might have to run a shield to blow more of the air towards the heat sink.

Last edited by ethan_hanus at Oct 2, 2011,