Open-Source Adjustable CC, CV Power Supply

Hey there!

So I have been working on a project that I think would interest a lot of us laser people (and other electronics hobbyists): a power supply that is constant-current and constant-voltage that is powered solely off of the 12V of an abandoned computer power supply (who can say that they don't have one of those?).

Anyway, I am almost done with the circuit design, but before I finish, I need some input from you guys: would you prefer a circuit where you have two separate settings, i.e. one is constant current, the other is constant voltage? Or would you prefer a single setting where it just balances it out according to the two knobs (like our current Mastech power supplies do)? The former is easier and I think it would be better, but it would make the circuit more complex and adds more to the user-end of the device (instead of just two knobs, it would be two knobs and a switch determining the state it's in).

Anyway, I'll keep you guys updated on this! Should be an interesting endeavor!

EDIT 1:

So I finished the board of the boost portion of the power supply. Anyone wanna check out the board arrangement to give me some feedback, if I arranged it properly, and so forth?

Here is the Eagle .brd file: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.brd

And here is the Eagle .sch file: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.sch

If you wanna check out the IC, it's the LTC3786 by Linear. Someone more experienced with board design would be more than welcome to help me out with this project!

EDIT 2:

So I finished up the schematic for the design - I went with a switch for CC or CV - I feel like it will provide more use that way. It *should* be adjustable from 0-24V and 0-5A, but that is still up for grabs, considering differences between real-life and simulations. My simulations *say* that it should be ~80-90% efficient (depending on the output), but I can't be certain what it will be like in real life.


EDIT 3:

Well, I finished the board of the CV circuit. Tomorrow I will do the CC circuit

Here are the files:
.brd: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.brd
.sch: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.sch

I think it's coming out alright... what do you guys think?

EDIT 4:

Alright, the board and schematic are done! Here they are:

.sch file: http://dl.dropbox.com/u/50345936/12V...able psu.sch
.brd file: http://dl.dropbox.com/u/50345936/12V...able psu.brd

What do you guys think? I don't have the money to order a board right now (and the next run won't be for a while anyway...), but once I get some money I will order the parts and board and test it out! It probably won't work right away (or ever - switching regulators hate me), but who knows?

EDIT 5:

The new, simpler version of the PSU is up!

.sch file: http://dl.dropbox.com/u/50345936/12vin adjustable psu 1.sch
.brd file: http://dl.dropbox.com/u/50345936/12vin adjustable psu 1.brd

This one is much simpler because it uses a SEPIC design for higher efficiency and buck-boost mode. What do you guys think about this one?

sounds fun... i also like the former

+1 bud for doing this because i couldnt ...

Hey, thanks. Working out some kinks on that version now in the simulation... so far, my CV part of the circuit is ideally getting ~90% efficiency, so probably ~80% in real life if I can get it working - MUCH better than the linear PSU. Now to finish up the CC!

Wolfman29 said:

Hey, thanks. Working out some kinks on that version now in the simulation... so far, my CV part of the circuit is ideally getting ~90% efficiency, so probably ~80% in real life if I can get it working - MUCH better than the linear PSU. Now to finish up the CC!

Click to expand...

will it be as stable as a linear psu? sorry if i sound stupid i kinda warned you already

As far as I can tell, it should be! Of course, there may be some ripple, but that's just a matter of larger output capacitors, which I can always adjust in size. However, my next step is designing the board... how should I do this?

Wolfman29 said:

As far as I can tell, it should be! Of course, there may be some ripple, but that's just a matter of larger output capacitors, which I can always adjust in size. However, my next step is designing the board... how should I do this?

Click to expand...

ahahh hope your asking someone else... does eagle cost money?

edit: yes it does....idk what else to tell you

Haha. Not the free version of Eagle Anyway, that was a rhetorical question. Probably going to work on board design tonight.

So I finished the board of the boost portion of the power supply. Anyone wanna check out the board arrangement to give me some feedback, if I arranged it properly, and so forth?

Here is the Eagle .brd file: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.brd

And here is the Eagle .sch file: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.sch

If you wanna check out the IC, it's the LT3786 by Linear. Someone more experienced with board design would be more than welcome to help me out with this project!

i knew that i was totally just tricking you.....no i wasnt shhh

Looking good. Keep up the cool project. Looking forward to when its done.:beer:

+2

So I think the next step will be ordering or crafting the 30V board and seeing if THAT works. If that works all fine and dandy, the next step will be adding in the constant voltage part. Then, finally, the constant current part. Hopefully I will have a working prototype in a couple of months, but for now, I need to figure out a good way to etch such a precision board.... And I also need to figure out a way to get the parts for this cheaply (been spending a lot of money lately -.-).

CV and CC wouldn't be that hard to do. Just some resistors and pots. Only problem is going to be getting a pot capable of handling the wattage. I guess putting a resistor in series with the pot will help quite a bit.

Also, your gonna need some beefy traces on your PCB. Also, In my opinion, having the ICs connected to the PCB via wires will help. Since your gonna need quite a bit of heatsinking.

LaZeRz said:

CV and CC wouldn't be that hard to do. Just some resistors and pots. Only problem is going to be getting a pot capable of handling the wattage. I guess putting a resistor in series with the pot will help quite a bit.

Also, your gonna need some beefy traces on your PCB. Also, In my opinion, having the ICs connected to the PCB via wires will help. Since your gonna need quite a bit of heatsinking.

Click to expand...

what i did for mine was i used 2 4W but they are like 5$ each :scared:

See, here's the thing - I am not doing a linear regulator. Those are remarkably inefficient and require huge wattage resistors. I have designed two separate switching regulators that use large resistance and low-value pots for cheapness and ease of sourcing for end-users.

But regarding the heatsinking... yeah. I know =[ In my board design, I have some 5mm wide traces. Haha. That's enough to handle 7A easily =p

EDIT: Well, I finished the board of the CV circuit. Tomorrow I will do the CC circuit

Here are the files: .brd: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.brd
.sch: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.sch

I think it's coming out alright... what do you guys think?

Alright, the board and schematic are done! Here they are:

.sch file: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.sch
.brd file: http://dl.dropbox.com/u/50345936/12Vin adjustable psu.brd

What do you guys think? I don't have the money to order a board right now (and the next run won't be for a while anyway...), but once I get some money I will order the parts and board and test it out! It probably won't work right away (or ever - switching regulators hate me), but who knows?

Cool project! Let me know when the group buy begins.

Or even a board run would be great!

Well, FIRST I need to make sure it works. So that may be a while due to funds :\