PWM to Analog converter circuit

Panyan said:
would it be safer using a molex input for the power rather than running multiple fans off one header
Click to expand...

Not safer as such as the circuit can't draw much more than about 0.4A but I have already planned to remove the two wires from the PWM connector and get power from a Molex as an option.

I'm also thinking about designing a second partner circuit that will drive fans without RPM feedback and this could then run off the Molex and you could perhaps run loads of 3 pin fans off that, still using the same PWm signal. I have the design ready, just need to breadboard it up. I could make a distribution board for it too, something like the one you might have seen in my videos. One one side the PWM to DC circuit and on the other a PWM to 12v circuit for the rest of your fans.

Every single fan controlled by your CPU temperature PWM curve. Sound interesting?

Panyan said:
ive heard lots of reports that pwm fans can click when run at under 12v (or not run on pwm mode), especially akasa apaches
Click to expand...

This shouldn't be the case as 4 pin and 3 pin fans don't really differ mechanically, just electronically, however it's not wholly relevant here as we won't be using 4 pin fans on the circuit.

Interesting though as I have a Apache and might whip it off and test that out. Mind you sometimes I notice it clicking even when running under PWM control. I knew I shouldn't have believed the Akasa hype, when I knew they were a bit pants from fans I've had from them before.
 
Last edited:
Tealc said:
I'm also thinking about designing a second partner circuit that will drive fans without RPM feedback and this could then run off the Molex and you could perhaps run loads of 3 pin fans off that, still using the same PWm signal. I have the design ready, just need to breadboard it up. I could make a distribution board for it too, something like the one you might have seen in my videos. One one side the PWM to DC circuit and on the other a PWM to 12v circuit for the rest of your fans.

Every single fan controlled by your CPU temperature PWM curve. Sound interesting?
Click to expand...

This interesting to me as currently I have 3 MOLEX coupled fans without RPM feeds.
 
I could probably do 0v or 3v up to 11v or something for this proposed second circuit. 0v-12v will be tricky indeed as you have voltage drops through transistors, regulators and stuff. A lot of fan controllers don't do full 12v anyway so I don't think this will be a huge problem. The big problem is that PWM fans have a different setup electronically and stay live all the time, just that the motor gets power as per duty cycle. What I'm proposing is switching the whole fan, including PCB on and off with the duty cycle. This may be problematic and I may have to go with some other method that switches high (11v) and low (say 3v) instead of 11v and 0v.

Ideally I'd like there to be an adjustable minimum fan speed for lowest duty cycle so you could choose the lowest RPM you want, eithr on a per fan or per board basis. There are some transistors with silly current ratings out there that could control dozens of fans off a single signal. Not quite sure how dozens of fans would interact with each other though.

I don't want to get too side tracked at the moment designing and testing more circuits until I've completed the original planned circuit though.
 
Last edited:
Tealc said:
I could probably do 0v or 3v up to 11v or something for this proposed second circuit. 0v-12v will be tricky indeed as you have voltage drops through transistors, regulators and stuff. A lot of fan controllers don't do full 12v anyway so I don't think this will be a huge problem. The big problem is that PWM fans have a different setup electronically and stay live all the time, just that the motor gets power as per duty cycle. What I'm proposing is switching the whole fan, including PCB on and off with the duty cycle. This may be problematic and I may have to go with some other method that switches high (11v) and low (say 3v) instead of 11v and 0v.

Ideally I'd like there to be an adjustable minimum fan speed for lowest duty cycle so you could choose the lowest RPM you want, eithr on a per fan or per board basis. There are some transistors with silly current ratings out there that could control dozens of fans off a single signal. Not quite sure how dozens of fans would interact with each other though.

I don't want to get too side tracked at the moment designing and testing more circuits until I've completed the original planned circuit though.
Click to expand...

I would say that a minimum voltage would have to be 3v not 0v as most fans won't run with voltages below 3v so if the PC got cool enough to drop to minimum then the fans would stall out.

Granted they'd start again once the temp rose again but surely stalling the fans isn't a great idea ?
 
i wonder if the fans would actually stall:

then fans would spin up as usual, then when the cycles dropped, the voltage would drop, but the flan blades still have momentum so they might keep going - i guess it depends on the quality of the fan tbh
 
panyan said:
i wonder if the fans would actually stall:

then fans would spin up as usual, then when the cycles dropped, the voltage would drop, but the flan blades still have momentum so they might keep going - i guess it depends on the quality of the fan tbh
Click to expand...

I have an old fan hooked up to one of those 1.5v - 12v multi-adaptors (ghetto-rigged to provide extra cooling for my Xbox). If I drop the voltage below 3v it stalls out within a couple of seconds. Switch it back to 3v and it restarts.
 
I knew I said I didn't want to get sidetracked but..

Hmm actually it's probably better if I don't have a 3 pin fan switching on and off 25,000 times a second and besides converting 5v PWM to 12v is trickier than I first thought. I've done 12v PWM to 12v fan and that's fine but the switching problem still remains. In the Oscilloscope graphic you can see me modifying the duty cycle up and down.

So if I can work towards 3v-11v (or thereabouts) I can use a Low Pass filter to voltage regulator circuit.

LP-1083.jpg


The triangle shaped component on the left receives a filtered PWM signal which basically smooths it out from it's bumpy 0v-5v shape to an average value between 0v and 5v. This then acts with the other components to output a reference voltage of the square LT1083 regulator. I've got plenty of the triangle components and other stuff and have ordered a LT1083 just to try it out.

The components at the top 1uF and 100 Ohm act as a buffer for when the circuit starts so it spins up to 100% for a brief time, it also acts as a buffer for when you change PWM duty cycle so it doesn't react too fast and cause noise variations. These should normally be 1k and 100uF. If I leave these as normal values it takes like 2 minutes just to drop down in simulation as it isn't real time.

The board for this circuit will be larger and drive loads of fans with adequate heatsinking on the regulator.

Under simulation I can throw over 5.5 Amps through the regulator without deflecting the output more than a few dozen millivolts. I'm not wholly sure if this simulation will bear out into the real world but will have to wait and see. LT1083 coming from China so will be a while and will give me a chance to finish the other circuit.

What I could do is mount the circuit on stripboard along with a few 3 pin headers for fans, and a Molex connector for power, either mounted or on wires. The board could sit somewhere like where a fan controller would go and it could be mounted in a box.
 
Last edited:
Tealc said:
The triangle shaped component on the left receives a filtered PWM signal which basically smooths it out from it's bumpy 0v-5v shape to an average value between 0v and 5v. This then acts with the other components to output a reference voltage of the square LT1083 regulator. I've got plenty of the triangle components and other stuff and have ordered a LT1083 just to try it out.
Click to expand...

Im assuming LT1083 stands for "Little Triangle Type:1083" :p

This is getting more and more epic Tealc :D
 
Haha.

It would be awesome if it did but in this case it's just Linear Technology number 1083.

Don't forget that this concept hasn't been tested properly yet and may not actually work.

Anyway if I get around to it Tuesday or Wednesday I will start making some originals with the Rpm feedback. I'm thinking this one would be useful for CPU coolers and can control an entire PCs fans if you use a few with splitters.

Who wants one? Any individual requests ie. Molex power etc I will fully test any I send out on my own PC.

We can organise things in trust.
 
Last edited:
Ok a couple of vidoes today.

First one is another aside is a LED strip PWM dimmer concept mentioned by Panyan as an idea.

Ever wanted your system LEDs to get brighter as your CPU warms up? Well this little circuit will do it for you.

I take the PWM signal and run it into a Darlington TIP112 transistor (just what I had to hand) and power the strip through the transistor collector connection. A Darlington is basically two transistors in series emitter to base so the current amplification can be 1000 times. If there are just a few LEDs a Darlington won't be needed and a normal power transistor would do.


The second is a video showing the circuit I built for Panyan.


So it's the same core circuit but with four fan headers on the board, it's powered by Molex and I've managed to get the full heatsink in place by shifting the B772 slightly. The resistors, although still a little upright are much neater and I will cover them with hot glue later.

I'm very happy how it's turned out and also very happy with the speed regulation, which allows a fast mid range, or a slightly slower mid range depending on which switch setting you choose. The low speed setting would also be useful for a single fan if desired.

Ideally the board will be mounted in a box of some kind or just insulated from the case. Most important is that the underside of the board is kept away from metal. I'd probably wrap in insulation tape and stick out of sight. I will leave that choice up to Panyan.
 
Indeed. The 'panyan' board looks awesome.

You mention a casing, isn't there a member on here with a small 3D printer ? As the unit is only small maybe he could at least knock you up a prototype to fitting purposes and then you could work together with the project. You produce the boards, he produces the casings and you could split the profits?

Maybe ask OcUK for a sales slot in MM?
 
Resident said:
Indeed. The 'panyan' board looks awesome.

You mention a casing, isn't there a member on here with a small 3D printer ? As the unit is only small maybe he could at least knock you up a prototype to fitting purposes and then you could work together with the project. You produce the boards, he produces the casings and you could split the profits?

Maybe ask OcUK for a sales slot in MM?
Click to expand...

I was thinking the casing should be more "low profile" so it is easier to tuck into the back of the case - my idea was to get some wide heatshrink and shrink it around the PCB so that it is insulated and the pcb components are safe from mechanical damage (pulling cables, closing sidepanels, etc)
 
gluegun is great for securing wires to board, small heatshrink for wires in/out, and large heatshrink for motherboard... large over compents won't shrink tight on ends so air can move over components. ;)
 
Stick it in a sock. It's not going to be seen so it just doesn't matter. :)

I will get measurements of the board for you. Sticking it all in a single heatshrink might be tricky though as the fans are all connected and add a fair bit to the height, although you could shrink it half way across the board. The B772's heatsink can be trimmed and even flattened down.

There are loads of electronic project boxes available of all different sizes available. Most are made of plastic and can be drilled to make holes for cable and stuff.
 
That's not a bad idea mate.

I would also advise a slot above the heatsink too, especially if you have loads of fans attached, not so much that it's sticking out but a hole so it can expel the warmer air.

Anyway I've ordered more fan header strips so I can do more like this. Currently I only have dual row, which I might be able to modify into single row but it's a bit of a hack.

Will check what size would be required. It's bigger than the Phanteks solution of course as it has more going on, and is mounted on stripboard which isn't the best space saving circuit board out there.
 
You must log in or register to reply here.
Back
Top Bottom