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PWM to Analog converter circuit

Discussion in 'Overclocking & Cooling' started by Tealc, Jul 8, 2012.

  1. Tealc

    Soldato

    Joined: Jul 13, 2009

    Posts: 6,847

    Location: Neath and Swansea

    PWM to 3 pin fan converter circuit

    Or how to finely control 3 pin fan/s with your 4 pin PWM motherboard/graphics card header and still get RPM feedback.

    Have PWM control without the annoying tick noise that PWM fans sometimes create.

    Drop me a message in trust, or post, if you want to ask me about making a circuit up for you. I've already made about 30 or 40 of these circuits for OcUK forum members.

    The start of this thread deals with the development of the converter, it includes pictures and many videos and also explanations of what's going on electronically and may be a bit heavy for some.

    However, this is the final product and this is what it does.

    • Control 3 pin fans directly from a 4 pin PWM fan header. That's CPU headers and GPU headers and any other PWM source in your PC.
    • Plugs into a 4 pin PWM fan header and spits out a smooth voltage the other side so you can control 3 pin fans with as small as a 1% change in duty cycle.
    • Has absolutely no PWM tick noise.
    • You still get RPM feedback.
    • It can control between 1 and 6 fans (depending on current rating), from less than 0.1A up to approx 1A via a adjustable screw.
    • It will adjust speed based on the PWM signal it gets from your CPU fan header or the graphics card header.
    • It uses less energy at low duty cycle. More efficient than many fan controllers.
    • It can be tucked behind the motherboard or in a 5.25" bay.
    • It can use Molex or fan header for power.
    • It can drive fans down to 150 RPM and right up to maximum speed.
    • It's home-made. Nothing quite like a ghetto mod :)
    • It's safe. The circuit takes only a very small load from the PWM pin.

    This is a version 2 I made for OcUK forum member.

    [​IMG]

    This one is designed for a Gelid Icy Vision and plugs into the graphics card to give the user fine control over their graphics card fan speed

    [​IMG]

    Here are two I made with 4 fan headers on the output.

    [​IMG]

    I fit a heatsink to the larger transistor as it can get a little warm when driving 2 or more fans.

    [​IMG]

    ...and an older one I made for another OcUK forum member who wanted Molex for power. This one shows the inside of the heatshrink and one with the components in view, some of these components are now SMD and mounted under the board.

    [​IMG]

    [​IMG]

    I can make these for a small cost to cover materials and postage and a bit for the time. Just drop me a trust message. I only make the latest versions these days, these come with all the trimmings and feature the best developments I've made on the circuit in the last two years.


    ---------------------------------------------------------------------------------------------------------------------------------
    And now the original first post.

    This thread details a small electronics project I'm currently developing to solve a problem I've had since building my rig a couple of years ago.

    So many CPU coolers come with 3 pin fans yet we all have 4 pin headers on our motherboards, it's a very puzzling situation and in some cases motherboard just don't have any 3 pin control support. So we then have to ditch the fans and buy some 4 pin PWM ones. My Gigabyte motherboard has far better control over 4 pin fans than 3 pin fans, indeed Easytune6 or the BIOS won't even begin to control my 3 pin fans and I have to use Speedfan. At the moment I have the fan ramp up and down between two values 600RPM and 1000 RPM. It's not ideal.

    I've always thought it'd be nice to be able to have the full 20-100% speed control of a 3 pin fan, just as we can have with 4 pin PWM fans, such as the Thermalright TY-140, Akasa Apache and Akasa Viper and other PWM fans.

    Now I'm just too tight to buy more fans, considering I have so many 3 pin fans, just to get this fine control so I've always thought it'd be cool to have some sort of converter. It is, however a little tricky.

    First thing's first. What is PWM? Pulse Width Modulation is a method of rapidly switching something on and off , varying the ratio of the time it is on related to off. The fan doesn't notice the switching because it's too fast, but other electronic items will.

    Consider the following image with a PWM signal at approx 25,000 times per second.

    [​IMG]

    It starts at 20% on/80% off, then goes to 50/50, rising to 80% on/20% off and finally 95% on/5% off. This is what a 4 pin PWM fan sees but cannot react fast enough to stop and start.

    Consider again, if you will, the following DC voltage trace.

    [​IMG]

    This is what a 3 pin fan sees.

    How can we take the first image trace and convert it into the second but have that line vary depending on the percentage that our motherboard tells it to run at? To further complicate things motherboard/graphics card PWM is just a 5v signal and carries nowhere near enough power to do anything useful. It's just a control signal, not a current source.


    Over in another thread Doyll was talking about an adaptor that Phanteks had sent him to do just that. My interest was piqued.

    So I set about simulating a circuit in Multisim (circuit simulation software from National Instruments) and it didn't work. Not even close.

    So after trying a few other ideas and realising that it's not going to be cheap or easy I came back to the original circuit, made a few adjustments, substituted my own transistor and got a really good result.

    I threw a few components onto a board and tested.

    [​IMG]

    This little circuit can drive a fan down to 150 RPM and all the way up to 100% of it's rated speed, just by the adjustment of the duty cycle. It's sensitive enough to change speed even with a small change to duty cycle, and what's even more useful is that I get full RPM feedback from the tach wire, something which was missing from so many other converter circuits.

    This little circuit can be plugged into the motherboard PWM header and drive fans, or it can be plugged into a graphics card PWM header and drive fans. Basically as long as you shove a decently high Hertz PWM signal into the circuit it'll work.


    So I've got more tests to come but this was one of my first. I hooked the circuit up to a 555 timer PWM circuit (on the left of the white board) and had it's tach output go to a counter circuit to light up the LEDs.

    It's poor quality as it's recorded on my iPod.



    I have hooked it up to my PC but light conditions were poor at the time so didn't record anything. I may upload a further video showing the amount of control I can have over the fan speed in a day or so. I am also hoping to load it up with 3 or so fans so I can to test it for capacity.

    Thanks to Doyll for the images and help. :)
     
    Last edited: Feb 27, 2014
  2. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    Any time mate. Any time. It's what makes life worth living. :)

    You did all the work. I just took a few pics and tried to read markings on components.

    Phanteks says theirs is good for 3 of their fans and said they would check with engineers and let me know what the load limit is. Time will tell.
     
    Last edited: Jul 8, 2012
  3. Tealc

    Soldato

    Joined: Jul 13, 2009

    Posts: 6,847

    Location: Neath and Swansea

    Tests with multiple fans were not encouraging. It seems that the voltage is shared across both fans as if they are in series. Tried with identical fans too.

    Doyll. Are you able to run more than one fan per converter? I'm wondering of my substitution of a MOSFET instead of a BJT is to blame here, or maybe it's just not good for more than one fan. When I hooked up two fans both fans would slow down noticeably and they'd have trouble starting.
     
  4. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    Will check it out this afternoon and let you know.
     
  5. moogle

    Wise Guy

    Joined: Nov 4, 2006

    Posts: 1,835

    Location: London

    Pretty awesome stuff, don't know why these convertors aren't available to purchase.
     
  6. Tealc

    Soldato

    Joined: Jul 13, 2009

    Posts: 6,847

    Location: Neath and Swansea

    Thanks mate. Just measured voltage drop and it's 3.5v down to 2.5v and at the top end 12v down to 8.5v so it's significant so you should see a marked difference in speed.

    I suppose it's not really super important as one converter per fan is no major hardship.

    Thinking about getting some S8050 in now though.


    I know. I'm sure they'd do well out of them, although more and more fans are PWM these days.
     
  7. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    Got same results.

    Voltage is shared in series .... mobo RPM reading is accurate (drops when using 2 fans) and can adjust using mobo with ET6 getting lower minimum RPM and same maximum RPM so work.. Just need multiple PWM motherboard to run fans in set of 2,3,4.

    I only have a single Y splitter so can't hook more fans... Phanteks said 3 of their fans was no problem on PWM adapter

    You are the electronics man, not me. But I don't see how to get full 12v PWM pulse to multiple fans.
     
  8. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    Indeed. Wouldn't be a long term market, but then what is in this business. Would seem a gold mine for them while it lasts.

    We can build our own, but obviously can't sell them. So anyone who can't source the bits and assemble their own is SOL.
     
  9. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    Addendum 10 minutes at low speed (640rpm) and can touch but not hold adapter. And that's out of heatsink. Don't think I want to run 3 fans with it.
     
  10. Tealc

    Soldato

    Joined: Jul 13, 2009

    Posts: 6,847

    Location: Neath and Swansea

    Interesting stuff. Not able to get 100% duty cycle on my bench PWM circuit so not seeing full speed with either fan. I've only got a two way splitter at the moment but think I will try 3 fans anyway, just for giggles.

    S8050 on hold until I can figure this out.

    I can measure current draw across fans with my meter so will see if it's that the current is restricted by the small transistor.
     
  11. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    You know where to get adapter if you need it. ;)
     
    Last edited: Jul 9, 2012
  12. Resident

    Wise Guy

    Joined: Mar 10, 2012

    Posts: 1,566

    Firstly I apologise if this is a REALLY dumb question.

    Right I have a 120mm generic fan which is powered by MOLEX. On inspection under the sticker over the PCB mounted on the motor there is a 3rd solder point.

    Would I be right in thinking I could attach a yellow cable to this for a speed reading and then use one of these adapters to control it via PWM.

    I ask because at the moment I have an Alpenfohn Matterhorn PURE fitted and my case exhaust fan sits about 2 inch behind it. As spinning at full speed (which I'm unsure of) it's sort of pulling air through the heatsink & I've had core temps (HWM Pro) as low as 14.5°C on idle.

    Unfortunately this is having an effect on the Alpenfohn fan as PWM is lowering the Alpenfohn fan speed that much that it's practically stalling out, I've had measured speeds as low as 397rpm when the minimum stated by Alpenfohn is ~500rpm.

    [​IMG]
     
  13. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    It is. ;)

    No. But it might be a RPM sensor.

    Unless your room is very very cold I doubt your core temp is 14.5c

    Don't think there is any danger of hurting PWM fan running on PWM by low speed.

    Next question? :)
     
  14. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    Would seem there should be a way to keep voltage at 12v without too much trouble, but then I know almost nothing about electronics.
     
  15. Tealc

    Soldato

    Joined: Jul 13, 2009

    Posts: 6,847

    Location: Neath and Swansea

    Fans in close proximity that are running at different speeds can have a drag effect on each other.

    The third wire is for a sensor output only. It's not useful as a control mechanism.

    The PWM design above uses the red and black power wires only.

    I hooked up two, then three 1000, 1000 & 1300 RPM fans and noted that the current drawn by the whole circuit only went up by about 20mA for each additional fan. So 120mA for one fan, 140mA for two and 160mA for three. It should be 120mA, 240mA, 360mA.

    Voltage drop was worse with three over two as well. Ohms law in effect I suppose. A finite amount of energy is available through the circuit and once you add more load it just shares that energy amongst all the loads, the rising mA reading accounts for the voltage drop. 12v@100mA is the same power as 10v@120mA and 8.5@140mA.

    The B772 was the hot component. I'm a little surprised that a 3 Amp rated transistor can't cope with a piddling 200mA load without getting scorching hot.

    I wonder if Phanteks have designed this device solely around their 140mm fan series, which has a known energy dissipation of max 0.15A.

    I think I might breadboard this circuit up again and substitute something else for B772.
     
  16. Resident

    Wise Guy

    Joined: Mar 10, 2012

    Posts: 1,566

    1. I meant the 3rd solder point being the RPM sensor :p

    2. 22.2°C currently. I've got WMP, PS CS3 & Firefox open and HWM states core temps are 22.0°C

    3. Ok. I just didn't like the idea of coming back to my PC and find that the fan stalled out and didn't restart, cooking my CPU in the process.

    Thanks. I'm relatively new to PWM fan control tbh. I assumed the speed sensor ouput was used.
     
    Last edited: Jul 9, 2012
  17. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    Seems something is amiss in Denmark (only a saying). I'll contact Phanteks and ask for some straight answers. Was so hot I could barely touch it.. too hot to have sealed up in heatshrink.. and that was only 2 fans, not the 3 they said it should handle with no problem.. And this is running their fans.
     
  18. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    The design only uses red & black to fan, but rpm from fan goes to motherboard and motherboard sends PWM trigger signal to design board. At least that's how my Phanteks one works.
     
  19. Tealc

    Soldato

    Joined: Jul 13, 2009

    Posts: 6,847

    Location: Neath and Swansea

    Will try another fan I have, a 2500 RPM 0.4A noisy one, and see what current it draws. I dismatled my counter circuit though so can't verify it's top speed unless I bring it inside.

    Might look at another circuit design. Bit more complicated (and expensive) this one and it has a voltage drop caused by the regulator.

    [​IMG]

    It simulates well enough. The varying voltage on the oscilloscope is from me adjusting the duty cycle. The LT1083 regulator drives the load and is rated at 7.5A so can drive a whole bunch of fans, in theory. It's only 12 components.
     
    Last edited: Apr 22, 2014
  20. doyll

    Soldato

    Joined: Jul 1, 2011

    Posts: 5,875

    you have email.
     


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