PC motherboard: PWM 4 pins to 3 Pins digital converter.

[Kiriakos-GR]

It must be on my luck ... the latest motherboard that I got looks unable to control the speed of any Non PWM  fan .

And so I must ask your help .

From my current searches on the net , found this interesting link  
an prologue at the 4 pin fans technology.
http://www.pavouk.org/hw/fan/en_fan4wire.html

And found also someone who made an circuitry , that he said that it works.
Another user looks to had confirm that, and another few was debating about it.
Because it uses the negative line to control the output voltage .
( picture at the bottom )




Two companies they had build this in to  (PCB) solution, and its marketed but for a price,
I like to make my own..  with your help ..

First (not wide)  marketed solution.
http://www.paqt.co.uk/docs/PaQ_PWM.pdf

Second .. wide marketed solution .. ( Nanoxia PWMX 3-Pin to 4-Pin PWM Converter )
http://www.svc.com/pwmx.html


Schematic found ...

  

[Mechatrommer]

just buy the fan Kiri. its not that expensive compared to if you blown out your MB. even cheaper, just buy the non PWM version, just connect to 12V-gnd, no hassle, just $3 or so. i dont understand your circuit, sorry.

[Kiriakos-GR]

i dont understand your circuit, sorry.

This circuit gets PWM pulses , and converts them to DC , and so the output drives the common fan,
and the fan speed  changes.

About the fan, I got the best ever 140mm for my cooler , but the damn motherboard, does not look to have speed control for both,  4 pin fans & 3 pins fans .
 
Here is the white paper , about PWM
http://www.formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf
 

[fsleeman]

You might want to check out this thread: https://www.eevblog.com/forum/index.php?topic=1366.0

I was trying to use a 555 timer to generate a PWM signal for a 4-wire CPU fan. I was able to generate the required signal but then realized I had a 3-wire fan instead! Although nobody proposed a solution for converting the 555's PWM signal to true DC voltage, the fan works even if accepting a PWM signal. The PWM frequency might need to be a lot lower than the 25-30k those fans usually uses depending on the physical properties of the fan and its electronics. Let me know if you find a simple PWM to DC solution, 555 or not.

[Time]

This seems like a strange way to do it but I don't see why it wouldnt work.  Changing the duty cycle would change the speed.

I might get corrected when I say this but I think this is a type of rudimentary chopper circuit.

Why not just breadboard it and find out if it works?

[scrat]

I don't know if I'm right at understanding what you need.
So please correct me if I'm wrong.
For a 4-wire fan, you have a 12V source which gets modulated (inside the fan) by the PWM signal (TTL).
Now, since old 3-wire fans were linearly regulated, you just have to convert your PWM signal into a proportional 0-12V source.

If until here all I said is right, the problem has at least two simple solutions, but since they seem to trivial to me, and you are all but stupid, I assume I have to be wrong somewhere.
However,
1) You can filter the PWM signal and go to the base of an npn BJT (emitter to ground), and linearly regulate the 12V supply (fan between +12V and collector). Speed sense feedback will provide control by the motherboard, even if transistor characteristic isn't linear. I'd put a
2) You can either put PWM signal directly to the gate of an NMOS (source to ground) and drive the fan in PWM, which shouldn't be a problem.

In both cases (but especially for the second), a back connected diode (cathode towards +12V supply) in parallel to the fan would be needed.
Open collector PWM output from the motherboard means you have to provide a pull-up from the 12V line (a resistor + 3.3V zener?).

I'd prefer the second solution, I think that motor phases inductance will do necessary filtering, although some LC could be needed.

[scrat]

I was making the same "mistake" as the circuit it was posted above (image): the sense signal is not referred to ground, which will cause wrong speed detection.

With two transistors (a small one and another a bit larger), it should work better.

[Kiriakos-GR]

Dear scrat  .. I am not an electronics engineer , so to use your generic info about making something.

I have post enough links at the first post, so to even see what I am looking for .
And not just that , the working circuitry of it, its pictured on this PDF ( Link also at my first message )
http://www.paqt.co.uk/docs/PaQ_PWM.pdf

All that I am asking are an clear simple schematic , with common to find parts , that will work.

In about 50 threads worldwide , all those people they stack in theory, and no one produces an simple working idea , like the schematic  posted above , or like the one pictured on the PDF .

That is four transistors , and few resistors.

If some one has the knowledge and the free time , to make something usable , he will become an public hero in the EEV and world wide .

If there is no new ideas on the table , I will had to try out the first schematic , and see if it works.

 

[Time]

in other words do it for him and don't worry about explaining it

[cyberfish]

First of all aren't your electrolytic capacitors backwards?

And you have a short from PWM input to ground through the base and emitter of the transistor.

[scrat]

Yesterday it was a long day, woke up at 5 and posted after midnight... and sorry for being long-winded as usual.

My idea was quite simple, I doubted it was too simple, indeed, and so I thought I was missing something.
With a few adjustments the posted schematic should work, if you have the patience to wait for me to look at it later. Unfortunately I don't have a fan by hand and the time to give it a try, but if "theory" is worth, it has to work. It could be even simpler, as I'm reading now about the tacho signal on the white paper, which I missed last night.

[Kiriakos-GR]

in other words do it for him and don't worry about explaining it

The correct description are ... do it for him , before Dave does it , and blog about it..  
Millions of young ones, that are exploring the computers hardware , have an major need for an practical solution, about this matter .

And I am included ..  as young one ...      

And, at the end , I will have just an spinning fan , and you .. the fame .  

[oPossum]

L1 and C1 may not be necessary for some fans.

[Kiriakos-GR]

Is that tested , or just an fresh idea  ? 

[oPossum]

Not tested. Just an idea. May require some tweaking.

[PeterG]

I have not bothered with the WPM controller my MB has. I simply use the fan from the heatsink connected to the 12v power with a diode in series. The diode drops the voltage just enough to silence the fan without loosing too much performance.

Its quick, easy, reliable and not over complicated.

Just my 2 cents.

Regards

[Zero999]

Not tested. Just an idea. May require some tweaking.

It's a buck converter, nothing new. The frequency, duty and inductance (not optional) need to be optimised for the load. There's no feedback so the output voltage will change as the load current changes.

[Mechatrommer]

Not tested. Just an idea. May require some tweaking.

this is the problem i think. even the 1st person has tested it and working, the second guy might not makes it work and start to blame and complaint, who knows, he may used different type part and fan? as opossum stated, tweaking is required, and to increase the success rate of the tweak.... experience is required

[Kiriakos-GR]

experience is required

Yes I agree, but from the part of the designer ...
He must be the experienced .

So to design an PWM demodulator ( 25KHz ) to DC  5 - 12 V .

And the funny part are , that this it has be made all ready , from some people in UK , and in China too.
 
And So, they are the experienced and capable , and all the rest on this planet are good,
only to just criticize or offer cheap rands.

And so ,  Shafri, save all those comments , or get to work with it ..

Every modern motherboard , has an PWM controller build in .
Every INTEL  fan  with four cables ,  has build in an demodulator .

I could probably  destroy the housing of an INTEL fan, so to get the PWM PCB , and connect just the wires that drives the motor it self , with to the cables of the New 3 Pin fan ...   ( but I hate the idea of destroying an good fan , just for that. )
      
And about the single - simple demodulator s ,  there is an portion of risk , as their output becomes like an switching power supply ,  that if it works out of control , it can possibly  fry one expensive  25$  140mm fan .

  

[jahonen]

If that buck converter design shorts out the switch transistor Q2, then voltage at the output is same than the supply voltage. Or if it becomes open, then output voltage seen by the fan is 0 volts. Either failure mode should be safe from fan perspective (of course assuming that fan can handle supply voltage).

Regards,
Janne

[oPossum]

All that I am asking are an clear simple schematic , with common to find parts , that will work.

That is what I posted. It will work. The uncertainty is how well it will work.

If there is no new ideas on the table , I will had to try out the first schematic , and see if it works.

That circuit is very poor design. Switching the ground lead of the fan will prevent the tach from working properly. There is no smoothing, just chopping. Using a 78L05 to bias the transistor is quite absurd - a resistor divider from the 12 v supply would be adequate.

It is unclear if the second design is supposed to be linear or chopper. There are no values on the cap and resistors. The high gain of the NPN prevents it from working well as linear, and the cap on the base prevents it from working well as a chopper. Will the fan tach work with a chopped supply?

If a circuit works for someone, that does not mean it will work for you or that it is a good design. Asking for something that has been built and tested is rather pointless. Reasonable design is far more important than an ugly hack that works for someone.

[Mechatrommer]

I'm looking forward to see an electrician with "thick hard" skin to get mess around with delicate electronics

[Kiriakos-GR]

If that buck converter design shorts out the switch transistor Q2, then voltage at the output is same than the supply voltage. Or if it becomes open, then output voltage seen by the fan is 0 volts. Either failure mode should be safe from fan perspective (of course assuming that fan can handle supply voltage).

Regards,
Janne

Thanks for the info ..   I feel a bit better by knowing this.

[Kiriakos-GR]

Is there any prediction , about the consumed energy of this buck converter ?

The on-board  fan header , looks in specs with:
12V 0.20A  ( 1700rpm) 90mm INTEL fan.
Or 12V 0.20A (1000rpm)  140mm.
 

 

[scrat]

It is unclear if the second design is supposed to be linear or chopper. There are no values on the cap and resistors. The high gain of the NPN prevents it from working well as linear, and the cap on the base prevents it from working well as a chopper. Will the fan tach work with a chopped supply?

I must admit my fast "design" has those big issues. And I was not considering the need for a tacho and phase-switching logic power supply, which can't be chopped. I was thinking at the motor windings only, which inductance is usually considered to be sufficiently high to filter out switching. The too high gain of NPN BJT can be avoided by putting a proper emitter resistance.

Your buck circuit is too much, in my opinion, I'd rather make it linear, avoiding the use of inductances. Let me make some calculation and a simulation to validate my circuit with the necessary modifications. Could this be accepted as a proof?