PWM to Analog converter circuit

Tealc said:
Thanks Resident.

Considering that far more complicated transistor circuits still work after more than 40 years in service I suspect that these things will last a good amount of time. The heatsink I use these days really prolongs the life of these things and in my tests only got warm to the touch

Naked transistors are not good when heat needs to be dissipated.

Later this week my aim is to build a couple of circuits up ready for when someone shows some interest, that way there'll be no appreciable delay.

Madmalkav sent me a name of a website that could spin me a few PCBs for a fairly decent cost so may look into that and as alternative to the veroboard I have been using. There's nothing wrong with veroboard of course and I quite like the long, easy to insulate footprint but it may make things easier to build. I could even do kits. If I redesign the footprint it would likely need a project box and the price would go up as they are pricey beasts. I can't really spin a custom shell like Phanteks do unless I had or could justify the expense/running costs of a 3D printer.
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If it's still the case next year then I'm looking to buy a 3D printer around Q1 of 2017.

I would be buying one this year however my fiance and I found out we're gonna be parents in Dec so every penny counts and frivolous purchases are out.
 
Tealc said:
(...) and I quite like the long, easy to insulate footprint but it may make things easier to build. (...)
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Well, a PCB with the silking will have all the traces isolated, only thing left will be the soldering contacts, easy to isolate with some readily available solutions in spray, tapes, etc... I've personally used some el cheapo thermal pads with good results.
 
Resident said:
I would be buying one this year however my fiance and I found out we're gonna be parents in Dec so every penny counts and frivolous purchases are out.
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Congrats Mike. That's excellent news.

madmalkav said:
Well, a PCB with the silking will have all the traces isolated, only thing left will be the soldering contacts, easy to isolate with some readily available solutions in spray, tapes, etc... I've personally used some el cheapo thermal pads with good results.
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That is true. Am looking into this. I've looked before, perhaps at UK options and they've been expensive. China, though can be had for less than £1 a board.
 
Just out of curiosity, would it be possible to somehow 'boost' the PWM signal system so it can control more fans? I really don't know exactly how PWM control works or why it's control is limited by fan PCB circuitry, I just know 8-10 PWM fans on a single PWM header is usually the limit for most PWM circuitry design, while other fan circuitry like Corsair only working with 2-4 fans. But I have no idea why it is what it is.
 
PWM signals are usually of limited current, 5mA absolute max, so when we draw current from multiple fans eventually the PWM signal will deteriorate until it can no longer trigger the attached fans.

Corsair may use BJT transistors rather than a Mosfet, or have some sort of pull down resistor that draws the current away. A BJT draws an amount proportional to its output current, somif it uses 100mA to drive the fan it may need to draw 1mA from the PWM source. I don't own any Corsair PWM fans to check what they use, or what the structure of the fan is.

To boost the PWM you'd use another transistor, typically a logic level mosfet to repeat the signal. A mosfet in an ideal world draws zero current from the source, although in reality it always draws something. You would take a 5mA PWM signal and use the other side of the mosfet that could allow you to draw several Amperes.

With my PWM converter circuit I draw some 40mA for the power transistor base, way above the 5mA allowed by Intel specification. The BS170 I use draws less than 1µA from the source, according to its data sheet. I've never measured the current draw from PWM and even if I wanted to I doubt I've got anything with the required resolution.
 
Took a look at my Apache PWM fan and it has a PNP BJT transistor ( W1P 01) on the PWM line. It is however in series with a 10k resistor, meaning that at maximum 0.5mA will flow through the transistor. I must say I was surprised to see a BJT there, not a little FET. Maybe it is a cost thing. FETs are more expensive than BJTs and as a system would generally have just one fan attached maybe the designers felt it wasn't really an issue.
 
Hi Tealc,

You still making these?

Would it be possible to get one made to control 4-5 fans to match the CPU cooler fan speed?
2 or 3 of the fans will be PWM while the other two will be 3Pin.

Thanks.
 
To do that you will need a PWM splitter with 3 or 4 sockets (for your fans and Tealc's adapter) I would use one that is powered directly from PSU so there is no chance of damaging the motherboard.

Tealc may be able to make it all as part of the adapter. ;)
 
Yes PSU power would be a given for 5 fans.

Yes I can do this.

Pass through for PWM fans, or a splitter might be easier. Speed monitoring of PWM fans and 3 pinners could be on separate wires to get your balance.
 
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Oh in that case you would just need a basic PWM converter for your PWM fans with the extra feedback connector.

You'd plug your PWM fans into your splitter. One of the spare spots would take the PWM converter circuit for your 3 pinners.

Or I could make a hub for the PWM fans if you prefer the neatness.

Something like this super word art
15nup0y.jpg
 
OK had another thought. What about this sort of concept.

rbbepu.jpg


Combined PCB with a line of PWM straight and a line of converted to 3 pin. Best of both worlds? A much neater solution.

PCB would be a little wider than my normal size but I think it won't be too much bigger, maybe 25mm wide or so.

And of course tach feedback off the 3 pinners which I didn't draw in.
 
That's the idea. Gives you a bit of scope towards adding extra fans.

I've never made a version like this before. It shouldn't present any issues provided you don't use fans that load down the PWM signal like certain Corsair fans have been known to do.
 
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