# So you want PWM control of your 3-pin fan?



## Lazzer408 (Feb 21, 2010)

I had to start a new thread because I couldn't update the old one.

Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.

Tested, working. Enjoy.


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## DirectorC (Feb 21, 2010)

Man I wish I had paid attention in Rocket Science class.


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## theorw (Feb 21, 2010)

Lazzer408 said:


> I had to start a new thread because I couldn't update the old one.
> 
> Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.
> 
> ...



Are there any photos of the mod available?So we need an N channel mosfet right?
And is that a diode?

Will any of these mosfets do http://www.markidis.gr/index.php?cPath=32_534_648&language=en
Which one would be best?


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## Lazzer408 (Feb 21, 2010)

theorw said:


> Are there any photos of the mod available?So we need an N channel mosfet right?
> And is that a diode?
> 
> Will any of these mosfets do http://www.markidis.gr/index.php?cPath=32_534_648&language=en
> Which one would be best?



I used an NTE2985 (30a TO220) because I had them on hand. Make sure you use a logic-level n-ch mosfet. The diode is a zener rated for 5.1v NTE5010A. Sorry for the quick drawing but that should get you going.

G = gate
D = drain
S = source

P = PWM
T = Tach
+ = 12v
- = GND


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## theorw (Feb 21, 2010)

Nice sketch makes complete sense...But it might be quite costly dont u think...mosfet and diode will get to 10EUR maybe..Still i might try this just for encyclopedical reasons!
Thanks again!

I suppose this is for 1 fan only right?


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## Lazzer408 (Feb 21, 2010)

If you get your power (and probably ground also) from a molex, you can put a dozen fans on it.

It's not expencive at all. I'm in the states but a cheap logic-level mosfet is $1, the diode maybe $0.10, and resistor $.05 but I buy a 10-pack at a time. It was very cheap to build. I've spent more on a package of zipties.

IRLz24 17a $0.62

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=IRLZ24PBF-ND


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## Lazzer408 (Feb 24, 2010)

Here's another version I've been working on. Feel free to make suggestions that may aid it's performance.

This is a high-side switched transistor version that has a minimum speed adjustment. This will allow ANY 3-pin fan to be adjusted to (roughly) meet Intel's minimum RPM spec of 30%.

My software didn't have a good TO220 NPN for the output transistor but any NPN capable of a couple amps should be fine. Radioshack has a TIP3055 that's good for up to .5a without a heatsink and a few amps if you sink it.


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## smashed_99cbr (Feb 24, 2010)

this has no feedback capabilites from what I can see


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## Fitseries3 (Feb 24, 2010)

i need to control a PWM fan.

any simple way to do that?

its a high current fan so i cant use a fan controller. 

i just need pwm signal generator that is variable.


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## Lazzer408 (Feb 25, 2010)

smashed_99cbr said:


> this has no feedback capabilites from what I can see



Feedback for what?



Fitseries3 said:


> i need to control a PWM fan.
> 
> any simple way to do that?
> 
> ...



Just a 2-wire fan? Doyou want the cheap and easy way or do you want to build it yourself?

http://www.electronickits.com/kit/complete/motor/ck1400.htm
or
http://www.electronickits.com/kit/complete/motor/k166.htm

Something like that can control a fan. The second link is a MUCH better design. Either one could have the potentiometer replaced with a thermistor.

To build your own, look into the SG3525 PWM IC but it has it's limitations as a motor controller. Mainly it can only go to 99% do to the dead-time built into the IC. It's designed for push-pull convertors but the output can be paralleled to give you more like 0-99% PWM.

Here you go. This would be the cats ass for cheap controllers.
http://www.virtualvillage.com/12v-1....html?utm_source=googlebase&utm_medium=shcomp

$10 bucks cheap enough for you?

http://cgi.ebay.com/LED-Dimmer-Adju...emQQptZLH_DefaultDomain_0?hash=item2a02f2011c


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## Frick (Feb 25, 2010)

DirectorC said:


> Man I wish I had paid attention in Rocket Science class.



No rocket science here mate, just basic electronics!


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## HammerON (Feb 25, 2010)

Lazzer408 said:


> Here's another version I've been working on. Feel free to make suggestions that may aid it's performance.
> 
> This is a high-side switched transistor version that has a minimum adjustment of 4~6v and ~2sec start-up pulse to get the fan going from a stop. This will allow ANY 3-pin fan to be adjusted to (roughly) meet Intel's minimum RPM spec of 30%.
> 
> ...



Thanks for your research on this topic
You have a lot more patience than I do~


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## Fitseries3 (Feb 25, 2010)

none of those will work.

i need pwm signal generator.

my fan is 4wire.

+,-,rpm,pwm


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## Lazzer408 (Feb 25, 2010)

Fitseries3 said:


> none of those will work.
> 
> i need pwm signal generator.
> 
> ...



The SG3525 is a PWM generator. You could even use a 555 to create a pulsetrain the fan would respond to.

Actually Fit, any motor controller would work. All the ones I showed you would work. Just put the controllers M- terminal to the PWM pin of the fan This will give you a PWM signal capable of driving a 4-pin fan. The difference would be that the control works backwards. A DC motor controller just grounds M- at the PWM width and frequency to raise the motor's speed. The Intel 4-pin signal pulls the PWM pin low to lower the fan's speed. Same as the DC motor controller just backwards so just turn the knob the other way.


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## ERazer (Mar 15, 2010)

sub


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## xXx Xander xXx (Feb 4, 2014)

I only sing up to thanks Lazzer408. The firts basic cirtcuit works very well. Thank you a lot!!. The only issue is the tachymeter, it display erratic values and the cooler varies alittle it speed constantly.

Thank you again!.

PS: Sorry for revive an old thread.


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## Lazzer408 (Feb 4, 2014)

xXx Xander xXx said:


> I only sing up to thanks Lazzer408. The firts basic cirtcuit works very well. Thank you a lot!!. The only issue is the tachymeter, it display erratic values and the cooler varies alittle it speed constantly.
> 
> Thank you again!.
> 
> PS: Sorry for revive an old thread.



It will due to the fan being low-side switched. In other words, the PWM is also chopping the tach.


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## xXx Xander xXx (Feb 4, 2014)

Lazzer408 said:


> It will due to the fan being low-side switched. In other words, the PWM is also chopping the tach.


Anyway, while that does not damage the fan... that makes the main work, control the fan. 
Thank you again!.


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## Aviator81 (Feb 19, 2014)

I also only signed up because of this thread, I've been looking for something like this for a little while because PWM fan selection is a lot more limited than 3-pin, so it would be great to be able to control a 3-pin as easily as a PWM. First of all, I wonder if you could point me towards some kind of crash course in basic electronics so I can understand what I'm doing a little better? I do have some experience working with designing and building circuits, but the last time I did anything like this was about a decade ago, so I'm beyond rusty.

Now, I am curious about your second circuit... You say it is high-side switched rather than low-side, so would it avoid the problems described by Xander? I would also like to expand it to handle more fans and be powered by molex in the way you mentioned earlier. How would you recommend going about this? Lastly, for now at least, I've noticed that commercial fan controllers and hubs almost always include some hefty caps with the reasoning described as this would allow them to handle more watts per channel. Neither of your circuits have any caps, so I'm wondering if you don't think they are needed, or if you just didn't add them because you weren't planning on running that much power through them?

Thanks.


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## fullinfusion (Feb 19, 2014)

Thanks but for the time and money, I think id just go buy new fans and be done with it.


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## Aviator81 (Feb 19, 2014)

fullinfusion said:


> Thanks but for the time and money, I think id just go buy new fans and be done with it.



I won't dispute the time you'd put into making something like this, but money is definitely another story indeed. I run 5 fans in my case, with the option for another 5 if I really wanted them. Just to replace the 5 I've already got with PWM versions of the same fans would cost over $100 whereas the parts that would go into this circuit would cost no more than $15 and probably less than $10. Add to that the fact that there are a lot more options when it comes to non-PWM fans than the reverse and something like this could give you a lot of flexibility in your case cooling design for a fairly low cost.


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## fullinfusion (Feb 19, 2014)

Oh I totally understand but for me and the local shops around they only sell bulk pcks of 50 piece's and the price is ridicules.


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## Aviator81 (Feb 19, 2014)

That would definitely make it difficult


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## fullinfusion (Feb 19, 2014)

Yeah does so. I love pulling out the soldering iron but like I said these guys are dicks. I have a 56" dlp led TV and the cap's keep blowing in the power supplie from the HS to close to them.

Do you think they'd sell me the caps i need for actuall value? Nope... costs me $125 just to get them to do the 15 min job,


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## Aviator81 (Feb 19, 2014)

Any chance of getting them from an online supplier? Might take a little extra time, but maybe it would solve the problem.


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## fullinfusion (Feb 19, 2014)

Aviator81 said:


> Any chance of getting them from an online supplier? Might take a little extra time, but maybe it would solve the problem.


Yeah I've looked around and same thing. Buy in bulk and still to much money.

Thats what I loved about Radio Shack when we had them in Canada. You could walk in buy a single Cap for 80 cents, now we have the Source and they sell packs of multiple Ohm and voltage parts and no pack is the same.

I swear they just bunch them up together and what ever falls into the package at the packing center you get!

I just find it easier to plug my regular fans into the motherboard hearers and set the speeds in the bios and be done.

I have a handful of temp probes I can hook into the mobo and place the sensor anywhere I want and have the bios on auto with monitoring and Bingo free PWM fans. I have one sensor plugged in and thats in the memory. Running 2666MHz with no fan needs to be watched.

The case I have, and the orientation of the fans, the case stays the same as the rooms ambient temp. Plus next to nada for dust 



Just to buy the parts for me where I live, Id probably spent $60 bucks to have the right values to make 2 fans.



Aviator81 said:


> I also only signed up because of this thread, I've been looking for something like this for a little while because PWM fan selection is a lot more limited than 3-pin, so it would be great to be able to control a 3-pin as easily as a PWM. First of all, I wonder if you could point me towards some kind of crash course in basic electronics so I can understand what I'm doing a little better? I do have some experience working with designing and building circuits, but the last time I did anything like this was about a decade ago, so I'm beyond rusty.
> 
> Now, I am curious about your second circuit... You say it is high-side switched rather than low-side, so would it avoid the problems described by Xander? I would also like to expand it to handle more fans and be powered by molex in the way you mentioned earlier. How would you recommend going about this? Lastly, for now at least, I've noticed that commercial fan controllers and hubs almost always include some hefty caps with the reasoning described as this would allow them to handle more watts per channel. Neither of your circuits have any caps, so I'm wondering if you don't think they are needed, or if you just didn't add them because you weren't planning on running that much power through them?
> 
> Thanks.


I didn't see you just joined TPU! good for you and a huge welcome from all of us awesome and helpful members!

We hope you stick around and enjoy your stay


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## Aviator81 (Feb 19, 2014)

fullinfusion said:


> I didn't see you just joined TPU! good for you and a huge welcome from all of us awesome and helpful members!
> 
> We hope you stick around and enjoy your stay



Thanks 

I take it that RadioShack.com doesn't ship outside of the US. That's really a shame considering that people who actually need this sort of stuff need specific parts in small quantities.

I did spend some time looking into fan controllers rather than trying to go this route and I think I came to the conclusion that those temp probes were more hassle than they were worth. I've heard that they aren't all that accurate, and in the case of the ones that are, you still have to mount them in places I'd prefer not to (like between the cpu and heatsink, or even under the cpu). Plus the fan control logic on the controllers seems to be pretty basic compared to the ability of software controllers to specify a non-linear fan profile based on core and case temperatures.


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## Ahhzz (Feb 19, 2014)

fullinfusion said:


> Just to buy the parts for me where I live, Id probably spent $60 bucks to have the right values to make 2 fans.



You know with this community here, there's probably a large quantity of people willing to hit their local shack or graingers or other supply depot and hook you up....


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## Aviator81 (Feb 20, 2014)

Ahhzz said:


> You know with this community here, there's probably a large quantity of people willing to hit their local shack or graingers or other supply depot and hook you up....



I'm new here and I'm already getting that impression... Was already thinking if I can get one of these things working I'd be happy to send you one


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## Velict (Jul 12, 2014)

Lazzer408 said:


> I had to start a new thread because I couldn't update the old one.
> 
> Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.
> 
> Tested, working. Enjoy.



So what if I add 10 fans to this one circuit? Do i need this circuit per fan, or will one mod work for multiple fans at once?


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## Shambles1980 (Jul 12, 2014)

why dont you just use speed fan? 
it can control 3 pin fan speeds just fine just set it up configure it and tell it to start minimized with windows...


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## Lazzer408 (Jul 12, 2014)

Velict said:


> So what if I add 10 fans to this one circuit? Do i need this circuit per fan, or will one mod work for multiple fans at once?



A motherboards fan header is limited to how much current it can provide.  With a higher current transistor and a large enough power source you can use as many fans as you want.


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## Velict (Jul 12, 2014)

http://www.mouser.com/Search/Produc...PBFvirtualkey57370000virtualkey942-IRL530NPBF

Rated for 17 amps, and fans will be driven by separate power source. So, No. of fans times their amps = transistor required?


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## Lazzer408 (Jul 12, 2014)

Yes but de-rate about 50%.

I chose the 530 because Radio Shack stocks it.

I'm going to stop looking for part numbers. I'm rushing through this and will likely create more problems then I'd be solving. Just find a mosfet that's turned on by 5v on the gate aka logic level mosfet.


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## Velict (Jul 12, 2014)

What does derate @ 50% mean? That the fans will spin at a minimum 50% from the PWM?


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## Velict (Jul 12, 2014)

Velict said:


> What does derate @ 50% mean? That the fans will spin at a minimum 50% from the PWM?


 
So, googling "derate factors" came up with some spreadsheets about amperage loss from temperature. Does this mean that, on the safe side, you'd want a higher amperage mosfet to meet the engineers specifications? I.e: "requires 17 amps, but has 50% degredation" so a 30 amp would be more suitable?


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## Lazzer408 (Jul 12, 2014)

Yes. It leaves a nice safety margin. If you have to control a 10a load, use a 20a device.

There are many variables in designing around mosfets used in switching circuits. Specs such as the turn-on turn-off delays and on resistance all add up. The manufactures use max ratings on components.


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## Velict (Jul 13, 2014)

Yes sir, thank you for the information! I will use the 17 amp ratings for another project. I just purchased Koolance fans http://koolance.com/fan-120x25mm-108cfm

and the 60v 30 amp mosfets from radioshack. I'm quite excited. Also some heatsinks, and thermal adhesive.


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## Lazzer408 (Jul 13, 2014)

Here's the Intel specs about their PWM design if you need it. http://www.formfactors.org/developer\specs\rev1_2_public.pdf

As if I don't already have a million things on my plate... One of these days I plan on making a PCB layout for a proper buffered circuit (powered off a Molex connector) to do exactly what you want. I have a use for one myself but it seems like everything I'm trying to accomplish these days gets delayed so don't hold your breath.


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## Velict (Jul 13, 2014)

Downloaded that PDF. Thanks a ton. Oh, I actually made a schematic... but I need to remake it because it was for an older version npn transistor... actually I think it was a modified schematic you made, but it uses two 10k resistors. I routed power to 10 fans, and made sure everything was in parallel, and your circuit comes before the fans. Here is a quick, horrible diagram. Pins and everything are off, but labeled so you can get the idea.


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## Velict (Jul 13, 2014)

Lazzer408 said:


> Here's the Intel specs about their PWM design if you need it. http://www.formfactors.org/developer\specs\rev1_2_public.pdf
> 
> As if I don't already have a million things on my plate... One of these days I plan on making a PCB layout for a proper buffered circuit (powered off a Molex connector) to do exactly what you want. I have a use for one myself but it seems like everything I'm trying to accomplish these days gets delayed so don't hold your breath.


 
I'll try to assist you, because this is a project i'm enjoying already. I'm going to keep updating this thread and try to keep it alive. Later today i'll post a cleaner schematic and people can poke at it. Most of us are adults here, we can't be online all the time! I'm currently deployed, even. hahahah


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## Lazzer408 (Jul 13, 2014)

Velict said:


> Downloaded that PDF. Thanks a ton. Oh, I actually made a schematic... but I need to remake it because it was for an older version npn transistor... actually I think it was a modified schematic you made, but it uses two 10k resistors. I routed power to 10 fans, and made sure everything was in parallel, and your circuit comes before the fans. Here is a quick, horrible diagram. Pins and everything are off, but labeled so you can get the idea.



Don't parallel the tachometer signals. It won't read the RPM correctly. Leave just one fan's tach connected and the RPM reading shown would represent the rest if they're all the same model.

I was actually talking about making a circuit board layout and having a few made so one could simply solder on their own components. If I go through the trouble, the design will be PWM to voltage to PWM and fully adjustable. The circuit, as it is now, is as simple as it can be to function and so inexperienced tinkerers could assembly it easily.

Go grab yourself a copy of Express PCB and Express Schematic to aid you in your designs and drawings. http://www.expresspcb.com/expresspcbhtm/download.htm


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## Velict (Jul 13, 2014)

I see where you're coming from. We can do variable resistors and swappable 556 sockets  http://www.circuitspecialists.com/machine-tooled-low-profile-ic-sockets

Oh, thanks for the schematics link


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## Velict (Jul 15, 2014)

Check it out


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## Lazzer408 (Jul 15, 2014)

You need to make some changes to your gate drive.  You don't need a logic-level FET if your driving it off a 556.  Replace the zener with a 10k resistor (keeps mosfet off).  Since the 556 can source and sink it's output so R2 isn't needed either.

If there is any flyback off the fans, don't forget to add a diode (in parallel with the fans) to protect the mosfet.

I personally HATE the 555 and 556 timers. >.<

EDIT - I see your using 5v for IC VCC.  Disregard the mods or move the zener to R1 to ground.


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## Velict (Jul 16, 2014)

Yeah, it's basically two circuits turned into one. Your schematic converts 3 pin to 4pin pwm, and the 556 boosts the signal FROM the motherboard to the fans, because there are so many fans it will degrade the signal, and the fans will only run at max speed.


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## Lazzer408 (Jul 16, 2014)

My circuit uses the motherboard's 4-pin PWM fan control to control 3-pin fans. There's no degrading of the PWM signal.

Are you trying to control many 4-pin PWM fans?


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## Velict (Jul 16, 2014)

Yes, 10 fans, at .28 amps each.


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## Lazzer408 (Jul 16, 2014)

And they are 4-pin fans?  If so, you may need a different circuit.


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## Velict (Jul 17, 2014)

They are three pin fans. They need to be converted to 4 pin.


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## Lazzer408 (Jul 17, 2014)

Ok just trying to get it straight. You don't need to "boost" the PWM signal. What is your reason for the 556?


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## Velict (Jul 17, 2014)

556 is to boost the PWM from the mobo to the 10 fans


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## Lazzer408 (Jul 17, 2014)

Then either I'm misunderstanding what your doing or your misunderstanding how the circuit functions. You don't need to boost the PWM signal. Intel's PWM spec is more then enough to sink gate drive.


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## Velict (Jul 18, 2014)

Sorry, i'm not explaining it all too well. Okay, so i've heard of issues where the intel pwm spec is not enough to drive more than 5 pwm fans at one time. Not power, but the PWM itself. The fans are powered through molex or an 8 pin adapter or something custom. http://www.overclockers.com/forums/showthread.php?t=700653


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## Lazzer408 (Jul 18, 2014)

It is true that the PWM signal has a limit but this circuit only uses the PWM signal to switch the mosfet's gate on and off.  What's on the other side of the mosfet is invisible to the PWM signal from the board.  You can connect as many fans as you want as long as the total current draw is less then 50% of the mosfet's rating -and- you keep the mosfet within it's thermal limit.

The way they are buffering the PWM signal (via. 556) is overly complex. You could do it with 2 transistors and two resistors. I only result to IC solutions when a circuit is to complex to make a discrete solution fit the task -and- a production IC dedicated to the task is available.


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## Velict (Jul 18, 2014)

...really. I had no idea. Is this because it's not multiple PWM fans? It's only going to drive one mosfet, not multiple?


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## Lazzer408 (Jul 18, 2014)

Correct.  Multiple PWM fans running off a single PWM signal can cause issues because the PWM spec calls for very little current on that pin.  Spec calls for a PWM fan to provide no more then 5.25v at no more then 20ma of current (if I remember right).  This is probably used for detecting the presence of the fan and limited to 5.25v in order to communicate with logic-level components on the board.  The 20ma current limit is likely due to the device switching the signal being very small like a surface mount transistor or an IC.  If you were to parallel, say, 5 PWM fans, the combined current could be too much for the device to switch and the device would be unable to sink (ground) the signal.

A board simply grounds PWM pin (in short pulses) to slow the fan.  The resistor in my mosfet circuit pulls the mosfet gate high (to turn it on) but only as high as the zener will allow.  When the motherboards PWM pin ground the gate, the mosfet turns off.  So all it's really doing is buffering the PWM signal to a level capable of driving fans directly.

It's really a pain in the ass that Intel made it as complicated as they did.  It uses much fewer components overall if they had just low side switched 3-pin fans.  Some boards can control speed on 3-pin headers.


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## Velict (Jul 18, 2014)

That is a very good explanation, thank you. Also, yes I wish more motherboards had 3 pin control. This whole project is to prepare for socket 2011-3 and x99 chipset.


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## Velict (Jul 27, 2014)

Lazzer408 said:


> I used an NTE2985 (30a TO220) because I had them on hand. Make sure you use a logic-level n-ch mosfet. The diode is a zener rated for 5.1v NTE5010A. Sorry for the quick drawing but that should get you going.
> 
> G = gate
> D = drain
> ...




Hey man! Parts came in. I built it today, tested it on one fan (still waiting on headers)
So what should I be looking at running it without PWM attached at the moment, just running only power?

What I saw was running stock, fan not attached to the circuit, NOTHING, i was able to start my fan at about 3volts, ran smooth and super low rpm.

When fan is attached to circuit, pwm not attached to motherboard YET, my fan starts spinning at around 4.8 volts, and is very very smooth and slow. Is this what I should be looking for?

Edit: Of course, at 12 volts, they were madmen... and i love it!


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## Lazzer408 (Jul 27, 2014)

The fan should be running at full speed if the PWM signal isn't attached.  Check for ~5v between gate and source.


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## Aquinus (Jul 27, 2014)

Lazzer408 said:


> It's really a pain in the ass that Intel made it as complicated as they did.  It uses much fewer components overall if they had just low side switched 3-pin fans.  Some boards can control speed on 3-pin headers.



In Intel's defense, running a low voltage and not a PWM + 12v makes it less likely that the motor will actually spin at low fan speeds. Applying short bursts of 12v versus constant low voltage will result in more consistent low speeds since the motor itself still realizing 12v, just less of it where a really low voltage like 3v or 2v might not even make the fan spin. So there are reason why a 4-pin design was made, but not if you don't want fine control of fan speeds and just rough control of it.


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## Lazzer408 (Jul 27, 2014)

Aquinus said:


> In Intel's defense, running a low voltage and not a PWM + 12v makes it less likely that the motor will actually spin at low fan speeds. Applying short bursts of 12v versus constant low voltage will result in more consistent low speeds since the motor itself still realizing 12v, just less of it where a really low voltage like 3v or 2v might not even make the fan spin. So there are reason why a 4-pin design was made, but not if you don't want fine control of fan speeds and just rough control of it.



The reason they use PWM is because it's a switched-mode method of controlling analog devices like motors, lamps, LEDs, etc. and that's second nature to digital electronics.  It's also more efficient and cost effective then a linear voltage regulator. The switching devices (carrying the current loads) are located in the fan so really all Intel is providing is a pulse train.  They left the actual control circuit in the hands of the fan manufacture. This leaves them free and clear of any issues caused by the design variations of fan manufactures.  As for start-up, that's on Intel's side.  The PWM signal from the board ramps from 100% to X% on start-up.


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## Velict (Jul 27, 2014)

update: i'm at work now, I'm testing for 5v across gate and source. I'll be back in 20 minutes.


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## Velict (Jul 28, 2014)

Alright! I tested the gate and source, but when I did, my multimeter would short out the mosfet and turn the fan off... so i did a bit of troubleshooting and I didn't connect the source to the diode and resistor... oops. Now, i'm seeing about 4.7 volts. All is well  Also, the previous issue of the fan starting at a higher voltage has been solved. Fans properly start at ~3v

Edit: uploaded pictures.... 

That grey stuff is dow corning 3145


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## Lazzer408 (Jul 29, 2014)

Glad you figured it out.  How is it handling the load of so many fans?


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## Velict (Jul 30, 2014)

Still waiting for the headers to test more than 1 fan.

but I have a question about your second schematic. The 30% modulated one.... is the fan on this schematic also supposed to run at max RPM when PWM is not connected? The same issue is happening, too. I'm using the 3904s and tip3055

Edit: R1 and r4 are receiving 12 volts, but r2 is only recieving 6v. Could I just replace the 10k resistor in this schematic with a variable 100k resistor?


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## Lazzer408 (Jul 30, 2014)

None of the fans are modulated by that circuit itself. The circuit is just a switch being modulated by the motherboard's PWM pin.

As for the PWM pin...

PWM high (5v or not connected) = Fan at 100%
PWM low (grounded by motherboard) = Fan at 0%
PWM 50% = Fan at 50% (6v)

The schematic you just posted is the mosfet version.  A bipolar transistor version -can- maintain a minimal fan speed by keeping the transistor in a partially conducting state so when PWM pin is low, the fan doesn't completely turn off.  You could also do this with a resistor but it will get hot since that is a linear method of idling the fans.

I drew them some time ago.  The transistor one was only an example of how the fan can be high-side switched so that the negative lead remains connected to the motherboard so the tach would function correctly.

The RIGHT way to do any of this (if you want complete control over everything) is to make a separate circuit that creates a PWM signal and have that circuit controlled by the motherboards PWM signal. An RC network could convert the motherboards PWM to a voltage and have that voltage control your PWM generator.

It's electronics. There's always 101 ways to skin a dalmatian. No wait...


----------



## Velict (Jul 30, 2014)

understandable, I have 556 timers to make my own pwm generator. But, i'll probably wait to do that. For now, what should I be seeing on the 30% circuit with the pwm not attached to the motherboard. 
My 50% circuit works amazingly. I'll be taking pictures of it tomorrow


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## Lazzer408 (Jul 30, 2014)

Looking at the schematic in post 7, you can probably eliminate R1 and Q2 and place the zener where Q2 was. When PWM calls for full speed, you should see ~11.45v on the fan due to the C-E voltage drop across Q1. When PWM calls for 0, the minimum speed is set by the 100k variable resistor.

Remember though, the post 7 circuit is linear when PWM calls for 0 fan speed and you have the 100k set to keep Q1 partially on.  It needs a proper heatsink.

The mosfet one shouldn't get hot at all and may work well without a heatsink at all.


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## Vario (Aug 28, 2014)

I am looking at running all 6 of my H1011's off of my motherboard's PWM CPU channel and doing away with my fan controller, could your circuit handle this? The fans are 12 volt .52amp 6.24 watts 3 pin.


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## Velict (Aug 28, 2014)

yes it will work

http://www.overclock.net/t/1505404/...o-pwm-56k-warning-courtesy-of-lazzer408/0_100


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## Vario (Aug 28, 2014)

Velict said:


> yes it will work
> 
> http://www.overclock.net/t/1505404/...o-pwm-56k-warning-courtesy-of-lazzer408/0_100


Thanks and yeah those koolance fans are really nice.


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## Lazzer408 (Sep 10, 2014)

I'm going to add another circuit to this thread that may help you guys.

This circuit CREATES a PWM signal that can be used to manually control 4-pin fans. The potentiometer is labeled "throttle" because this was part of a DC motor controller I'm designing.

Frequency is controlled by C1. R7 may not be required. By replacing the potentiometer with a thermistor, the circuit can monitor temperature and control the fans accordingly. R5 and R6 would then have to be adjusted to suit your thermistor and the temperature range.

VCC is incorrectly labled 5v. The circuit runs on just about anything but was designed for 12v operation.


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## Vario (Sep 18, 2014)

Lazzer, can you give me feedback on whether this circuit looks okay and won't blow up my motherboard?




















I used Velict's diagram





Thank you.


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## Lazzer408 (Sep 18, 2014)

Did you bench test it?


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## Vario (Sep 18, 2014)

All I have is a digital multimeter.   Could you suggest a way to test it?  I could use a battery for the 12v source but not sure where to get a pwm input, maybe my dead h100i?


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## Lazzer408 (Sep 18, 2014)

Connect it to your 12v source.  PWM lead should have ~5v on it.  With PWM lead disconnected, the fan should run full speed.  With the PWM lead grounded, the fan will stop.

I'll look over your pics tonight.

Velict's diagram looks fine other then the diode's anode connection doesn't have a dot on it.


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## Vario (Sep 19, 2014)

I plugged in a 12v trickle charger and was able to run a single fan on it. Haven't done any more tests at the moment.  I think the fan was running full speed.  I'll try messing with the PWM lead.


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## Vario (Sep 19, 2014)

My DMM measured a bit over 4 volts (4.10ish) on the PWM lead.  When grounded, the fan turned off.  I also ran this with a few Deltas and San Aces, 8 fans total, they all seemed to run full bore with no PWM connected.

I haven't measured the voltage of the trickle charger.

I am pretty excited.


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## Lazzer408 (Sep 19, 2014)

Sounds like it's working fine.  Good job.


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## Vario (Sep 19, 2014)

Lazzer408 said:


> Sounds like it's working fine.  Good job.


Thanks for the help, I am waiting for a 4 pin male-male fan cable to hook it up.


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## OneMoar (Sep 19, 2014)

yall realize this thread is from 2010 right ?


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## Lazzer408 (Sep 19, 2014)

What's that have to do with anything?


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## OneMoar (Sep 19, 2014)

a little something called thread necromancy


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## Lazzer408 (Sep 19, 2014)

Which hurts who in what way?  Information doesn't have a "sell-by" date.  If people are still benefiting from the thread, it's not dead.


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## Vario (Sep 19, 2014)

I am glad the thread was brought to the front.  Its very helpful, learned a lot.

I hope to solve some fan control issues I am having with this circuit.

Update:

I am running it now.  My San Ace 109R1212H1011 will barely run at idle, and only if they are alone in the circuit. If I run two high powered fans they turn off.  A Delta WFB1212HH won't spin at all.  A Koolance 12038HBK will run very low voltage but at higher pwm, they start to sing in a high pitched whine that sounds terrible.

I am using the parts list shown here:
http://www.overclock.net/t/1505404/guide-convert-3-pin-fan-to-pwm-56k-warning-courtesy-of-lazzer408

edit: if it runs bursts of 12v, and it isn't spinning up, then maybe the PWM circuit for the motherboard isn't compatible with the power demands of these fans because it doesn't switch on frequently enough?

edit2: Different mosfet?

should i try constructing your minimum speed version?
http://www.techpowerup.com/forums/t...ontrol-of-your-3-pin-fan.115752/#post-1779591  Does that switch more frequently?


----------



## Lazzer408 (Sep 19, 2014)

Are you using a logic-level mosfet?


----------



## Vario (Sep 19, 2014)

Yes I am using an N Channel NTE 2985


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## Lazzer408 (Sep 19, 2014)

Not a very good component but RDS(on) at 4v is .07 ohms so you 4.1v is plenty of gate voltage.  NTE parts are junk (for future reference) but not the cause of your problem.

The switching frequency is a function of the motherboard and should be around ~20khz.  What do the fans do if you pull the connector from the motherboard?


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## Random Murderer (Sep 19, 2014)

Lazzer408 said:


> What do the fans do if you pull the connector from the motherboard?


Could also be that his "trickle charger" is not supplying enough current on the 12V in for those high-current fans.
@Vario,  have you tried powering this directly from a 4-pin Molex?


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## Lazzer408 (Sep 19, 2014)

He mentioned in #79 that he tried the charger... "with a few Deltas and San Aces, 8 fans total, they all seemed to run full bore with no PWM connected".  I think it's in his computer now.


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## Vario (Sep 19, 2014)

Random Murderer said:


> Could also be that his "trickle charger" is not supplying enough current on the 12V in for those high-current fans.
> @Vario,  have you tried powering this directly from a 4-pin Molex?



In observing this behavior, it was plugged into the 4 pin molex and the motherboards PWM. My "trickle charger" was only used for testing the circuit on my work table. I don't see why it needs to be in quotes unless you aim to make me look backward.  Also a trickle charger should have plenty of current, I believe this one can do 8 amps.

Its possible its less than 4.1v now that its running on the power supply.


Lazzer408 said:


> Not a very good component but RDS(on) at 4v is .07 ohms so you 4.1v is plenty of gate voltage.  NTE parts are junk (for future reference) but not the cause of your problem.
> 
> The switching frequency is a function of the motherboard and should be around ~20khz.  What do the fans do if you pull the connector from the motherboard?




If I pull connector from the motherboard they run full speed.

I could measure the voltage on the PWM lead with it running on my power supply and no 4 pin input. However, i believe the gate is modulating because the smaller lower powered fans do spin.

-It also seemed like running the h1011 on the single tach reporting 3 pin and the koolance 12038hbk on one of the 7 non-tach 3 pins, the h1011 wouldn't spin at all but the koolance would.  The h1011 alone would spin, but very slowly.

-Koolances seemed better at managing the lower speeds but at higher pwm frequency they sang (whine), while the San Aces did not make this whine.  The single San Ace barely spun at the lowest setting.

-So its possible this motherboard's fan curve sucks.


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## Lazzer408 (Sep 19, 2014)

I think it's in quotes because we have no idea of knowing what type of charger it is. If it's a trickle charger for lead acid batteries, then it's likely much higher then 12v and it's not DC either.

If the fans run full speed with the PWM unplugged, your gate drive is ok.  What happens with you go into the BIOS and set fans at a constant speed?


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## Vario (Sep 19, 2014)

Lazzer408 said:


> I think it's in quotes because we have no idea of knowing what type of charger it is. If it's a trickle charger for lead acid batteries, then it's likely much higher then 12v and it's not DC either.
> 
> If the fans run full speed with the PWM unplugged, your gate drive is ok.  What happens with you go into the BIOS and set fans at a constant speed?


Yes its a trickle charger for a battery.  It read as DC current on my multimeter.

I'll try setting fans for constant speed.


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## Lazzer408 (Sep 19, 2014)

Put your meter on AC and measure that charger. Read anything? If so, that's the ripple in the DC caused by the chargers lack of filtering (they don't need it).

Next, place a capacitor in parallel with the charger and measure the DC voltage. Is it higher? If so, that's the peak DC voltage coming from the charger.


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## Vario (Sep 19, 2014)

Lazzer408 said:


> Put your meter on AC and measure that charger. Read anything? If so, that's the ripple in the DC caused by the chargers lack of filtering (they don't need it).
> 
> Next, place a capacitor in parallel with the charger and measure the DC voltage. Is it higher? If so, that's the peak DC voltage coming from the charger.


I'll check this out next.


Lazzer408 said:


> I think it's in quotes because we have no idea of knowing what type of charger it is. If it's a trickle charger for lead acid batteries, then it's likely much higher then 12v and it's not DC either.
> 
> If the fans run full speed with the PWM unplugged, your gate drive is ok.  What happens with you go into the BIOS and set fans at a constant speed?



So far, voltage mode = fans run full power. disabled fan control = fans run at full power, pwm mode = they operate as described above.  These are the fan control options I have with this mobo.

Thank you for the help with this.

edit:
I am presently thinking the fan curve is too weak for the h1011 to spin.  In my testing, they work as PWM should, where they spin up at boot, but then stop completely.
I am running two san aces and nothing else, with one of the san aces in the tach reporting 3 pin.
Is it possible to increase the switching frequency to counteract the motherboard's weak fan curve?

edit2:
-car battery trickle charger has 13.1v dc and 4.32v ac, didn't test with cap.
-I tested circuit on computer with five 3 pin cougar fans and it worked fine, the 5 cougars varied speed properly.  These cougar fans are very wimpy, in comparison to the San Ace and Deltas.


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## Lazzer408 (Sep 20, 2014)

The PWM frequency is a function of the motherboard. All the board does is ground the PWM pin at varying widths. If you don't have complete control over the fan curves in your BIOS, this circuit may not work for you.

The "correct" way to control a fan (using Intel's PWM spec) is a more complicated circuit.  My attempt was to simplify it as much as possible but it may not be 100% compatible with every fan.

One thing about PWM and power switching circuits is the layout of the PCB is very important. Wires jumping all over the place isn't good. What you see as a wire with 0-ohms is actually a resistor and when switching high current loads very quickly will product all sorts of voltage transients and noise that can interfere with the circuit functioning correctly. This may be the case when you start paralleling high current fans. Some suggestions would be to put a capacitor as close to your molex connector as possible. Also place the mosfet so the source pin is as close to the capacitor's negative terminal as you can get it. Try and keep all your grounds connected at the same point at the capacitor's negative terminal. That's about all I can suggest at this point.


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## Vario (Sep 20, 2014)

Thanks for the advice.  I would put the capacitor between the mosfet's source and the molex ground?

I think you are right about the fan curves in bios.  Gigabyte's PWM curve isn't very curvy.

Would there be a way to just increase the duty cycle?


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## Lazzer408 (Sep 20, 2014)

The capacitor should be placed in parallel with your supply voltage.

Duty cycle (pulse width) is controlled by the motherboard.  If you can't adjust it in the BIOS then there's nothing you can do about it.


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## Vario (Sep 20, 2014)

Lazzer408 said:


> The capacitor should be placed in parallel with your supply voltage.
> 
> Duty cycle (pulse width) is controlled by the motherboard.  If you can't adjust it in the BIOS then there's nothing you can do about it.


Okay thanks.  Damn.


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## madmalkav (Jan 28, 2015)

I bought a Gelic Icy Vision for my wife GPU just to discover that even if it comes with a VGA PWM connector it doesn't have the PWM pin, nor do the fans support PWM. Both fans are cable to a single VGA PWM connector.

I will love to make a version of this circuit  for controlling these fans with the graphic card VGA signal. I only need to control this two fans so I think I can save a lot of space in connectors etc. But I know nothing about electronics, I'm the kind of guy that solder stuff without understanding how it really works, so any help will be appreciated.


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## tedlas (Mar 22, 2015)

Lazzer408 said:


> I had to start a new thread because I couldn't update the old one.
> 
> Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.
> 
> Tested, working. Enjoy.



I am very very happy I found this thread! I have been playing around inside of a simulator type thing, but it doesn't seem right. 

Can someone explain what is going on? Is everything happening the way it should?


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## dmax (Apr 12, 2015)

It is my belief that the information w.r.t. this design is incorrect, for these reasons:
That by locating the PWM Mosfet in the Earth line, it can 'Modulate' the Hall Effect device, and that
by so doing, produces a PWM signal on the Tacho.  feed lead.
I think that the  (Intel) spec. requires the PWM control to be in the Pos. line, and therefore, the supply
voltage is relatively uninfected; That it can run from 5 or 12 volt line.
Here is a link, for anyone needing further info:-
http://www.maximintegrated.com/en/app-notes/index.mvp/id/3530
http://para.maximintegrated.com/en/results.mvp?fam=fan_cntrl


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## Lazzer408 (Apr 12, 2015)

dmax said:


> It is my belief that the information w.r.t. this design is incorrect, for these reasons:
> That by locating the PWM Mosfet in the Earth line, it can 'Modulate' the Hall Effect device, and that
> by so doing, produces a PWM signal on the Tacho.  feed lead.
> I think that the  (Intel) spec. requires the PWM control to be in the Pos. line, and therefore, the supply
> ...



All of that had been mentioned in the thread.


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## dmax (Apr 13, 2015)

The reason that I came to this link, is because I was looking for a quick design to run a (5 volt) Blower (think laptop)
in an HTPC, and most available fans are of a 3 wire configuration.
I  have now re-read this thread, and appreciate that some of the points had been covered.
In your response (57), you said that Intel had made it 'complicated', but they didn't, it was the only Logical way that the 
system could be developed; By that, I mean that one would Naturally have the Tacho. output, referenced to Ground,
and therefore, the Hall Effect Device, will be Low-sided, which is where the Rotor coils are switched.
Therefore, the only place to PWM the motor, is on the High-side.
Maybe, I don't see that it was ever an option to Low-side the PWM control on a 3 wire motor.
As an update, it would be appreciated if you could present a circuit, which incorporates a High-sided Mosfet element,
as these are better suited to this process, than any bi-polar transistor.
Regards.


----------



## Lazzer408 (Apr 13, 2015)

High side switching via. MOSFET will require gate drive >12v. Use a BJT transistor. Because it's switched mode, losses are minimal. Typically (.6V*A)*PWM=dissipation. If you had 3 amps worth of fans (a lot), and PWM is 100%, you will only have ~1.8w of heat to dissipate from the transistor.

I'm totally swamped in projects right now. I don't think I can get to a schematic any time soon but BJTs are fairly easy to drive. A small TO92 device to drive a TO220 device is fairly simple.


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## Lazzer408 (Apr 13, 2015)

It's going to be something along these lines. Not sure how it will work with the PWM signal being 5v but a low/hi signal driving this circuit will give you a low/hi out. Choose a Q1 large enough to drive your load, Choose R2 to drive enough current into Q1's base. Q2 should be large enough to shunt Q1's base current. R1 can be 10k or higher or even left out.


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## Black Boy (Jun 16, 2015)

Lazzer408 said:


> It's going to be something along these lines. Not sure how it will work with the PWM signal being 5v but a low/hi signal driving this circuit will give you a low/hi out. Choose a Q1 large enough to drive your load, Choose R2 to drive enough current into Q1's base. Q2 should be large enough to shunt Q1's base current. R1 can be 10k or higher or even left out.



Hi Lazzer

So I want to use this circuit for my ASUS M5A97Evo, and my water cooling CM nepton 120XL pump that has 3 wires.
I noticed my cooler pump is not running at full speed while conected to the motherboard. So can i use your first circuit with a 12V molex connector?
Somthing like image attached.

Sorry for my bad english


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## R-T-B (Jun 16, 2015)

Black Boy said:


> Hi Lazzer
> 
> So I want to use this circuit for my ASUS M5A97Evo, and my water colling CM nepton 120XL pump that has 3 wire.
> I noticed my cooler pump is not running at full speed while conected to motherboard. So can i use your first circuit with a 12V molex connector?
> ...



I can't answer your question, but your english is fine just so you know.


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## dmax (Jun 16, 2015)

R-T-B said:


> I can't answer your question, but your english is fine just so you know.


Just a quick reply; You do not need anything as complicated as the above circuit, as your Pump has only 3 wires, there is NO PWM
control signal, so, just use the 3 connector plug, into you Mother-board, where the 3rd wire will indicate the Pump motor Speed.
A google search linked me to this article:-
http://www.tomshardware.co.uk/answers/id-2051351/fan-fan-header-problem-asus-m5a97.html
So it may be worth checking the settings in your BIOS.
Regards,


----------



## Black Boy (Jun 16, 2015)

dmax said:


> Just a quick reply; You do not need anything as complicated as the above circuit, as your Pump has only 3 wires, there is NO PWM
> control signal, so, just use the 3 connector plug, into you Mother-board, where the 3rd wire will indicate the Pump motor Speed.
> A google search linked me to this article:-
> http://www.tomshardware.co.uk/answers/id-2051351/fan-fan-header-problem-asus-m5a97.html
> ...


No actually my bigger problem is that my motherboard doesn't support fan voltage control through CPU connector and it's running at full speed all the time, and here is my second problem, my pump can't reach its max speed through motherboard CPU connector.


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## dmax (Jun 16, 2015)

Black Boy said:


> No actually my bigger problem is that my motherboard dose not support fan voltage control through CPU connector and its running at full speed all the time, and there's my second problem, my pump can't reach its max speed through motherboard CPU connector.


Let's be Very specific; Fan Speed control is not regulated by Voltage, but by PWM, and, by convention, any 3 pin fan connector WILL power the fan at Full voltage,
and hence, Full Speed; The only variation, is via. the 4th wire, which regulates the Fan Speed by virtue of the control circuit of the Fans internal Ground connection.
(There is an indication that some units seem to be 'better' powered from the Molex (chassis) plug, but I'm not convinced that, That is the problem).
Your original complaint, was that the Pump was not running at Full Speed; Do you know this as a fact, i.e. via. an On-screen, Tacho readout?
The circuit you submitted, will not work, for various reasons, that is why any Added control, Has to be in the 12 volt line (all due to backward compatibility).
If your Cooler pump is not running at full speed, does it do so when connected directly to the 12 volt connector, and can you explain the difference.
Regards,


----------



## andrew124c41 (Aug 11, 2015)

Lazzer408 said:


> I had to start a new thread because I couldn't update the old one.
> 
> Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.
> 
> Tested, working. Enjoy.


I have a bunch of M5A97 MBs LE and non LE R2.0 with AMD processors.  I am new at doing PC builds and I bought a bunch of coolermaster led 120s that run a 2000 rpm.  I want to run 4 fans intake and 3 fans exhaust.  These are 3 pin fans.  I have heard but am not certain, that the PWM MB control in bios or fanExpert will only slow them down to 60%.  I thought that perhaps using two of these circuits running the fans in parallel to the two separate case fan headers would work.  It is not clear to me why one can draw power directly from the PSU yet have control...guess it is the MOSFET.

I saw a circuit with simply an NPN power transitor and a 100 k potentiometer but I don't think the voltage would drop below 5 volts.


----------



## dmax (Aug 11, 2015)

I still maintain that this circuit will not function correctly, with standard Computer Fans, for the reasons in my previous reply.
By Pulsing the Ground Lead, you interfere with the Switching Transistors which energise the Motor Coils; That is why the control HAS to be in the 12 volt supply line,
all due to backward compatibility.


----------



## andrew124c41 (Aug 11, 2015)

dmax said:


> I still maintain that this circuit will not function correctly, with standard Computer Fans, for the reasons in my previous reply.
> By Pulsing the Ground Lead, you interfere with the Switching Transistors which energise the Motor Coils; That is why the control HAS to be in the 12 volt supply line,
> all due to backward compatibility.


I have been able to control 3 pin fans by decreasing the voltage with resistance.  I assume you are talking about 4 pin fans.  It was my understanding that the fans are the same in terms of their being simple DC motors, just that the PWM fans' speed is controlled by duty cycle.  They have a PWM circuit built right into the fan.  I thought this circuit merely duplicated what is in the fan.  I am referring to the circuit that Blackboy posted?  Will that work for me.  Also, I had heard that PWM would only bring the speed down to 60%.  I may just have to get rid of these fans unless anyone has a solution.  I have attached a two component circuit and wonder if it will work. for what I am trying to do...I would have two of these


----------



## Pill Monster (Aug 11, 2015)

andrew124c41 said:


> I have a bunch of M5A97 MBs LE and non LE R2.0 with AMD processors.  I am new at doing PC builds and I bought a bunch of coolermaster led 120s that run a 2000 rpm.  I want to run 4 fans intake and 3 fans exhaust.  These are 3 pin fans.  I have heard but am not certain, that the PWM MB control in bios or fanExpert will only slow them down to 60%.  I thought that perhaps using two of these circuits running the fans in parallel to the two separate case fan headers would work.  It is not clear to me why one can draw power directly from the PSU yet have control...guess it is the MOSFET.
> 
> I saw a circuit with simply an NPN power transitor and a 100 k potentiometer but I don't think the voltage would drop below 5 volts.


This is true you can slow them down to 60 but they only run between 60 and 100 duty cycle.
The screwed up thing about these ASUS boards is they have a min/max temp setting in BIOS but only 3 pin fan headers on the board. lol and you can't set the temp below 40c.

But I have 7/8 casefans running on a HAF X and they do a fine job, not too noisy and not too quiet. 







Oh instead of AI SUITE you can use Argus Monitor to control fan speed if you wish, or AMDOD but that doesn't work as good.


----------



## dmax (Aug 12, 2015)

andrew124c41 said:


> I have been able to control 3 pin fans by decreasing the voltage with resistance.  I assume you are talking about 4 pin fans.  It was my understanding that the fans are the same in terms of their being simple DC motors, just that the PWM fans' speed is controlled by duty cycle.  They have a PWM circuit built right into the fan.  I thought this circuit merely duplicated what is in the fan.  I am referring to the circuit that Blackboy posted?  Will that work for me.  Also, I had heard that PWM would only bring the speed down to 60%.  I may just have to get rid of these fans unless anyone has a solution.  I have attached a two component circuit and wonder if it will work. for what I am trying to do...I would have two of these





andrew124c41 said:


> I have been able to control 3 pin fans by decreasing the voltage with resistance.  I assume you are talking about 4 pin fans.  It was my understanding that the fans are the same in terms of their being simple DC motors, just that the PWM fans' speed is controlled by duty cycle.  They have a PWM circuit built right into the fan.  I thought this circuit merely duplicated what is in the fan.  I am referring to the circuit that Blackboy posted?  Will that work for me.  Also, I had heard that PWM would only bring the speed down to 60%.  I may just have to get rid of these fans unless anyone has a solution.  I have attached a two component circuit and wonder if it will work. for what I am trying to do...I would have two of these


----------



## dmax (Aug 12, 2015)

The fact that The/A, motor runs on DC, only describes part of its Specification.
ALL (as far as I am aware) use Switched Transistor's in the ground lead, which is controlled
by a Hall Effect sensor (Switch), and a 3 wire fan works on 12 volt, (or 5 volt in laptops).
It IS possible to reduce the operating voltage, but this is a notoriously problematic solution, that is
why PWM (4 wire) fans run at 12 volts, with a varying PWM signal, (THEY DO NOT REDUCE THE VOLTAGE).
If I remember correctly, the Intel spec. requires the Electronic control, to push a continuous12volts for 1-2 seconds, in order to overcome the Start-up resistance (sort-of, like Stiction).
In order for you to use 3 wire motors (IF your Motherboard does not have PWM Case Fan Header), is
to find a circuit, which converts the Output of a Thermocouple, to PWM, and feed THAT to the (12 volt) 
supply line,; Though it would probably be easier to use a Fan which has a Remote Thermal Sensor.


----------



## andrew124c41 (Aug 12, 2015)

Pill Monster said:


> This is true you can slow them down to 60 but they only run between 60 and 100 duty cycle.
> The screwed up thing about these ASUS boards is they have a min/max temp setting in BIOS but only 3 pin fan headers on the board. lol and you can't set the temp below 40c.
> 
> But I have 7/8 casefans running on a HAF X and they do a fine job, not too noisy and not too quiet.
> ...




With 60 percent duty cycle, do you know how much they will slow down from 2,000 rpm?


dmax said:


> The fact that The/A, motor runs on DC, only describes part of its Specification.
> ALL (as far as I am aware) use Switched Transistor's in the ground lead, which is controlled
> by a Hall Effect sensor (Switch), and a 3 wire fan works on 12 volt, (or 5 volt in laptops).
> It IS possible to reduce the operating voltage, but this is a notoriously problematic solution, that is
> ...



The motherboards I have use 4 pin PWM control.  As I understand, 2 lead fans simply run on 12 v.  What you are refering to is the inertia, the startup volaage could be around 5 v plus or minus a volt or two, fan dependant.  3 pin fans as you said use the third lead to utilize the Hall  effect to determine speeed.  The forth lead gives the information so to speak, to use pulse width to manefest as a duty cycle.

I am just trying to figure out how, having purchased these 2,000 rpm fans, I might be able to bring them down to around 800 rpm.  Sure, I could do it permently with a large resister for each set of fans...but simple control would be nice.  I was just trying to find out if the circuit that started this thread by Lazer408 can work for my situation.  I also poste a pic of a simple two compnant schematic with a power npn and a 100 ohm pot that should be able to do this manually...I wonder if that will work.


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## dmax (Aug 12, 2015)

NO, you cannot rely upon them Starting on 5-7 volts, for the reason that I alluded to in my previous reply.
In order for them to start reliably, they must start at 12 volts, then be reduced.
The stupid aspect w.r.t. using a power resistor, is that it WILL generate vast amounts of Heat, (relatively).
If you were to use anything, then reference the following:-
http://www.ebay.co.uk/itm/DC-12V-40...832?pt=LH_DefaultDomain_3&hash=item3cff1d3488


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## Pill Monster (Aug 12, 2015)

Sorry, seems I told a lie. I just double checked and at least 3 of the headers are actually 4 pin.

It's the fans which are 3 pin. 

This applies to Sabertooth and M5A97, I have both.


And I should mention I have a 12v .40A Fractal Design 140mm which needs a push start every now and again if I use 60% duty.


But the 200mm Coolermasters which are 12v .30A fire up every time


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## dmax (Aug 13, 2015)

Further to my above recommendation, I would suggest the following:-
http://www.ebay.co.uk/itm/PWM-DC-12...d-Controller-for-Brushless-Fan-/261978142374?
Or:-
http://www.ebay.co.uk/itm/DC-Motor-...oller-Switch-6V-12V-24V-3A-PWM-/252035720628?
as it runs at 21KHz, which is better than the 15kHz of the previous one.
Ideally, you would be looking for 25kHz, as any 'cogging' will be above the upper range of Audibility.


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## RejZoR (Aug 13, 2015)

It's usually smart to attach some sort of heatsink to the mosfet "backside". Half of the chipset cooler should do the trick. Or an aluminium VRAM heatsink (cube shaped). Stuff that you can easily obtain from anywhere.


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## andrew124c41 (Aug 13, 2015)

Pill Monster said:


> Sorry, seems I told a lie. I just double checked and at least 3 of the headers are actually 4 pin.
> 
> It's the fans which are 3 pin.
> 
> ...


Forgive me, I am not sure I understand.
You have the same MB and 3 pin fans as I do.
How are you controlling the 3 pin fans?
Is it just with the software or are you using a circuit?
Finally, at 2,000 RPM, how fast do you think my 120s will go?


dmax said:


> Further to my above recommendation, I would suggest the following:-
> http://www.ebay.co.uk/itm/PWM-DC-12...d-Controller-for-Brushless-Fan-/261978142374?
> Or:-
> http://www.ebay.co.uk/itm/DC-Motor-...oller-Switch-6V-12V-24V-3A-PWM-/252035720628?
> ...


@dmax 
Forgive me, maybe you did not understand what I was saying....I agree with you.  I was refering to the reason that they cannot be started at 5 v....the inherent inertia.  Once going, they can be reduced.

I had seen the PWM controlers that you refert to on Amazon in the US.  However, I was not sure if they would work.  The power transitor I picked is capable of dissipating the heat.

*What I have been trying to find out are two things:

1) Will the circuit with the MOSFET work with my MB.  That is, will the fan speed be controlled and can it be manually controlled via the UEIF or FanExpert?  Can I get the speed below 1,000 rpm this way?
2) If #1 will not work, then I either want to use the power transister or one of the pwm controllers you suggested...one for each set of fans intake and exhaust.*


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## Pill Monster (Aug 13, 2015)

andrew124c41 said:


> Forgive me, I am not sure I understand.
> You have the same MB and 3 pin fans as I do.
> How are you controlling the 3 pin fans?
> Is it just with the software or are you using a circuit?
> Finally, at 2,000 RPM, how fast do you think my 120s will go?


 OK, the chassis fan headers can control 4pin pwm fans but in DC, not pwm.. The CPU fan header is the only true PWM.

I control case fan speed by adjusting min/max duty cycle, (not really duty cycle but that's what bios says lol) speed stays constant but at min 60 I hardly hear my fans.

In saying that, I had a 120mm Coolermaster which got a bit noisy.... so I removed it. Not sure on your specific fans.






Also, did you ask about a water pump, I can't remember.....but if you did, what u can do is get one of these: https://shop.ekwb.com/ek-dcp-4-0-pwm-12v-dc-pwm-pump

It uses a molex plug for power, but comes with a 4pin pwm connector. Plug the connector into the CPU fan header and you have temp controlled fan speed.


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## andrew124c41 (Aug 13, 2015)

I just went back to the manual.  My MBs do not support voltage contol....no way to do that1


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## dmax (Aug 13, 2015)

Whether it is the Resistor OR a Transistor, it still needs to dissipate the heat, that is why Switch Mode supplies are used today; As one runs at, say, 55% efficiency,
and the other at 90%
A MOSFET circuit will only work, if it's designed to be installed in the 12 volt supply line, as has been stated previously.
If your board is the M5A97, then it DOES have 4 Pin Chassis Fan connectors, which will be
PWM; If you have 2 or 3 pin fans, then use the Controllers that I Referenced earlier, on the 
Molex 12 volt supply line.


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## Pill Monster (Aug 13, 2015)

andrew124c41 said:


> I just went back to the manual.  My MBs do not support voltage contol....no way to do that1


If your board is an M5A97 it does. Isn't that what you have? 

It even states that it in the manual.  Duty cycle is voltage control for the chassis fans.


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## andrew124c41 (Aug 13, 2015)

Pill Monster said:


> If your board is an M5A97 it does. Isn't that what you have?
> 
> It even states that it in the manual.  Duty cycle is voltage control for the chassis fans.


M5A97 LE R2.0


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## Pill Monster (Aug 13, 2015)

andrew124c41 said:


> M5A97 LE R2.0


Ah OK.  Yeah LE being the budget version 970 it may not.


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## dmax (Aug 13, 2015)

Just occurred to me, you could take one of the PWM units, and Hack it, by replacing the Variable Pot. with a Thermistor;
But it would need some experimentation.
The LE version has the same 3 x 4 Pin Chassis fan connectors.


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## Florent (Feb 11, 2017)

Thanks for this post that I've used for my 3pin CPU Fan and it works.
I found a used MOSFET transistor referenced NEC 2SK3299 that fits fine, look ahead !


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## Vario (Feb 15, 2017)

Florent said:


> Thanks for this post that I've used for my 3pin CPU Fan and it works.
> I found a used MOSFET transistor referenced NEC 2SK3299 that fits fine, look ahead !


Nice, very compact too.  What model fan?


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## Florent (Feb 16, 2017)

The fan is a cooler master i117 in place of the standard Intel too noisy.


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## Tanotis (Mar 8, 2017)

Hello, its been great to know that this thread is living so long and still being commented and a great thread to know the PWM thing and electronic hack nicely. If anybody listen then help me to answer for the following. I drawn a similar circuit suggested by Lazzer408 on a online simulator and tried to run it, It was simulated nicely without any error. Can anybody suggest me any for mods, or can I go ahead to make on the board for real test?


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## Welni (Jul 20, 2017)

Tanotis said:


> Hello, its been great to know that this thread is living so long and still being commented and a great thread to know the PWM thing and electronic hack nicely. If anybody listen then help me to answer for the following. I drawn a similar circuit suggested by Lazzer408 on a online simulator and tried to run it, It was simulated nicely without any error. Can anybody suggest me any for mods, or can I go ahead to make on the board for real test?
> View attachment 84940



I'm sorry, i'm not an expert, but if you still need it, you might want a bigger resistor at the output. This one will dissipate 1,44W at 12V output. I'd also think about a cap to flatten the voltage. Alternations in the voltage may couse the fan to stick to certain harmonic frequencies of the signal.

On the other hand i have a question. Why don't we just use a high switch mosfet driven by the PWM signal and flatten the output voltage with a low pass RC filter? Does the tacho readout work only on 12V(H) and 0V(L) signals? Or can it be downgraded to like 5V(H) and 0V(L)?
I hope i'll get my reply sooner than the last guy


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## norq (Sep 11, 2017)

Lazzer408 said:


> I had to start a new thread because I couldn't update the old one.
> 
> Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.
> 
> Tested, working. Enjoy.



First, many thanks for sharing. Sorry for necro, but I built this circuit and used a SUP50N03 (instead of the IRL530N) which can source hefty amps even at Vgs=2v and has low Rds(on): http://www.vishay.com/docs/66570/sup50n03.pdf ... it doesn't say it's a logic level mosfet, but specs show it should work just fine, unless I'm mistaken! Please correct me.

I want to use this to drive 6 three-pin fans with high static pressure, each drawing up to 0.5A. The PWM from my motherboard swings between 0.08 and 3.5v.

At the output of this circuit (where the fans connect) I don't get a constant voltage but the same pwm signal, swinging between 0 and 12v (rather than 3.5v). It kind of works - the fans seem to have a large-ish capacitance on the input which almost converts the PWM-like signal into a constant voltage. However, the rotor of some of them, when all 6 are in operation (driven by this circuit) makes an audible clicking noise at lower speed - they don't make that clicking noise if I supply them with an actual constant voltage to achieve the same rotation speed. I suspect the noise is from one of the coils inside the small circuit board of the fan, rather than the actual rotor.

Is this sort of pwm-like signal safe for the fans? Can anyone comment please?


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## Welni (Sep 12, 2017)

Hi there, 
The clicking sound shouldn't be a problem. In fact, many cheap PWM controlled fans make it. It happens because of the steep signal edges. Better fans have some integrated ICs to power the motor more gently and reduce the sound level. Anyway if you check datasheets of same fans, one with PWM control and one without, the PWM fan should be rated as louder. (fe. BQ pure wings 2 are rated for 19.2dB and the PWM version for 20.2dB). 
And if you're interested, high side switching + cap works well on arduino, so you can try it with your PC.


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## P!nkpanther (Sep 18, 2017)

I developed a tested solution for this problem and published it here in a new thread:
https://www.techpowerup.com/forums/...ump-using-4-pin-pwm-control-from-mobo.237118/


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## norq (Oct 10, 2017)

Welni said:


> Hi there,
> The clicking sound shouldn't be a problem. In fact, many cheap PWM controlled fans make it. It happens because of the steep signal edges. Better fans have some integrated ICs to power the motor more gently and reduce the sound level. Anyway if you check datasheets of same fans, one with PWM control and one without, the PWM fan should be rated as louder. (fe. BQ pure wings 2 are rated for 19.2dB and the PWM version for 20.2dB).
> And if you're interested, high side switching + cap works well on arduino, so you can try it with your PC.



Thanks for replying. I used a SUP50N03 which can source 5+ amps at 2.4v, and goes up to 50+ amps with higher Vgs (it's also a fast switching mosfet). I built the circuit in the 1st post to drive 6 powerful fans rated at 12v, 5.4w. At full speed these fans together draw about 2.5 amps.

The mosfet is:

cold to the touch when the PWM duty cycle is higher than 80% ... happily sourcing 2.5 amps and staying cold.
warm to the touch around 60% pwm duty cycle
super hot to the touch below 40% pwm duty cycle ... can't keep my finger on it for more than a fraction of a second
even hotter at 20% pwm duty cycle.
Using a scope I noticed (as expected) that the output signal is another PWM signal with the same frequency and duty signal as the motherboard's, but sweeping 0-12v.

Why does it get so hot at low pwm duty cycles, given that the mosfet switches on/off with the same frequency? Is it just because the time it stays on is shorter (bigger harmonics, so higher AC load?). Can I do something about it with simple components?

Any simple circuit (without using level converters, ADCs, etc) such that the output is close to a level voltage, rather than a PWM signal? That would also be better for my fans since with this PWM-like output signal, not all of my fans spin at the same speed for the same PWM duty cycle (I was expecting some variation, as they essentially switch on and off, but not as much).

EDIT: I found this (replace hxxp with http - the forum doesn't allow me to post links): hxxp://forum.arduino.cc/index.php?topic=12651.msg95289#msg95289

By the way - the circuit in the above hxxp link will not output a full 12v to the fans as there will always be a Vth drop on the final mosfet in that configuration when the bipolar is off (unless I'm missing something) ... it should output a fairly clean analogue voltage level though, rather than pwm like signal


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## norq (Sep 3, 2018)

For the simple circuit in the first post is there any danger of killing the fan in time? Some of the fans when mounted onto this circuit are clicking since the fan receives a square wave between 0v and 12v

I had a bunch of Sunon Maglev MEC0251V1 fans (pretty powerful 120x25mm fan) mounted on this circuit, and some of them no longer respond to the signal ... they either spin very slowly at the same speed when the PWM has <100% duty cycle regardless of PWM value, or spin at full speed when PWM=100% (i.e. no square wave, just 12V).

I'm trying to rule out whether it was dust or the circuit that killed them.


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## John Naylor (Sep 3, 2018)

PWM Clicking / Hum has been around since PWM ... the need for such a circuit has been eclipsed as Fan Hub PCBs are readily available and inexpensive.

https://www.phanteksusa.com/collections/accessories/products/phanteks-fan-hub

How long were you using the circuit ?


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## norq (Sep 3, 2018)

1 year. I'm aware alternatives exist, I'd just like to know if said circuit can kill fans


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## norq (Sep 7, 2018)

bump, if i may?


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## iwik (Jan 31, 2020)

Hi, I was searching for solution how to control my 3 pin fan using PWM and found this thread.  I want to buy (not DIY) simple and cheap solution. It seems there is _PHANTEKS PWM FAN HUB_. This hub is for multiple fans. It allows you to control 3 pin fans using 4 pin pwm. http://www.phanteks.com/assets/manuals/PH-PWHUB.pdf http://www.phanteks.com/PH-PWHUB.html It cost about $15.
For single device I found _Phobya 4Pin PWM to 3Pin Transformer. _It is quite expensive ($12) on amazon https://www.amazon.com/gp/offer-listing/B01HQBNXYK
but for me local dealers seems to have better price ($3) https://www.aquatuning.sk/vodne-chl...5/phobya-4pin-pwm-auf-3pin-transformer-single

I hope this saves lot of searching if someone else in future found this thread


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## kapone32 (Jan 31, 2020)

iwik said:


> Hi, I was searching for solution how to control my 3 pin fan using PWM and found this thread.  I want to buy (not DIY) simple and cheap solution. It seems there is _PHANTEKS PWM FAN HUB_. This hub is for multiple fans. It allows you to control 3 pin fans using 4 pin pwm. http://www.phanteks.com/assets/manuals/PH-PWHUB.pdf http://www.phanteks.com/PH-PWHUB.html It cost about $15.
> For single device I found _Phobya 4Pin PWM to 3Pin Transformer. _It is quite expensive ($12) on amazon https://www.amazon.com/gp/offer-listing/B01HQBNXYK
> but for me local dealers seems to have better price ($3) https://www.aquatuning.sk/vodne-chl...5/phobya-4pin-pwm-auf-3pin-transformer-single
> 
> I hope this saves lot of searching if someone else in future found this thread



A lot of modern motherboards have DC/PWM right on the header and you can usually adjust it in the BIOS. It even works for pumps.


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