Control FAN with PWM (using LM317)

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi guys. I've tried to control some pc fan with PWM, but the noise is too annoying.

So, I've do a little circuit with a potentiometer, some resistor a capacitor and a LM317...it works perfectly...manually of couse...but...the voltage can change only if I regulate the potentiometer...is there a way to use arduino PWM (or another output Analogic/Digital) to use with that circuit? Of cuirse, potentiometer change resistance, but arduino pin out can only change voltage...

Sorry for my bad bad English..
Thanks

2

You need to filter the PWM to make it a DC voltage:-

http://www.thebox.myzen.co.uk/Tutorial/PWM.html
You can apply this to your voltage regulator.

3

Is better use a opctocoupler, I have 2 tensions (5V USB an 12V for FAN)??

Next, I see a little schematic for aruindo that use a LM317 and an op-ampli..is necessary??

Thanks again

4

Is better use a opctocoupler

No.

I see a little schematic for aruindo that use a LM317 and an op-ampli

So I probe with my physic power and see the circuit that you see. Nop my powers mustn't work on Mondays.

5

HI!
I've tried a schematics that I found on forum (tnx Rugged)
http://www.ruggedcircuits.com/images/sch14.png

but it wont work..
The transistor is very hot and the fan do anyway noise..
Why?

Little question...how I must use an op-ampli in this scheme for the LM317 ?!

6

So I probe with my physic power and see the circuit that you see. Nop my powers mustn't work on Mondays.

LOL ;D

7

but it wont work..
The transistor is very hot

There is no transistor in this circuit so how can it get hot?

8

Sorry, I mean the op-ampli..beacuse my electronic supply haven't TLV2371 he give me an alternative, if I remember correct, an LM324 (sorry I away from the circuit :D).

Anyway, I thinks that op-ampli is for getting more of the 5V from the PWM...I'm wrong?

Sorry for bad English..
Thanks again for patience

9

So did you change the pin out of the schematic to the new device. The LM324 has four op amps in it and that circuit uses only one.
Old circuit - LM324
power 7 - 4
ground 4 - 11
+ve input 3 - 3
-ve input 2 - 2
output 6 - 1

If the op amp is connected correctly there is no way it will get hot. It's purpose is just to act as filter and amplifier for the voltage regulator. The voltage regulator might get warm in this circuit but nothing else.

10

Thanks, in the evening I try to see if the pin out is link correctly.

11

If you have wired it up wrong and it got hot you probably fried the chip.

12

Hi!
After some months I ask a little question...
If I want to put an optoisolator like in that circuit , I must put an external +5V source or I can use the already present 12V plus a resistor?

Thanks a lot.

13

As I said before there is no need for an opto isolator for your application.
This will work as drawn but there is no filter to smooth the voltage so you might not get very good low speed on your fan.

14

Yes I know, but my question is regard the first circuit:
http://www.ruggedcircuits.com/images/sch14.png

For saving arduino if the fans break or other "bad thing", can be useful insert an optoisolator in the first circuit (with LM317) or is useless?

15

For saving arduino if the fans break or other "bad thing",

The only fault an opto isolator would protect you from is if the transistor failed with a base to collector short circuit. This is an unlikely fault, transistors are more likely to fail open circuit or short circuit between emitter and collector. I would not consider it worth while, but then it is not my circuit.

16

Perfect!
Thanks for the exhaustive response :wink: