Sorry, i have another PSU design question!

[f.aiseur]

Hi everyone!

Yes i am quite sorry to start a new thread for PSU design, but i couldnt find anything close to what i am after...
For a specific project (Bozak CMA-10-2DL clone, by Fabric Astronaut : https://fabricastronautblog.wordpress.com/2016/07/24/pathos-dj-mixer-pt-1/), i need a specific PSU.
First build i made, i found a simple 40VDC psu, and its all good.

But i started a second one, and for this one i have more needs.

The idea is to include a 3band isolator and some VU meters. So on top of the 40V DC/1A supply, i also need +/- 18V (not sure about how much current).

Someone told me that i'd need two transformers for this kind of thing, so i bought two different PSUs, each with onboard transformer.
But this solution is not great to me, specially for space consideration.

After looking for a while at available options, on some builders facebook group, here on GDIY, everywhere, i couldnt find something suitable.
(oh i didnt mention... i dont want to spend hundreds on some overkill commercial psu, ideally i'd find a bare pcb to populate myself).

And in the end i started to use Kicad, thinking i could make my own design, and learn a few things along the way.

There is a thousand PSU designs available online, which makes it a bit confusing. But most of them are either adjustable +/- lm317/lm337, either 48VDC phantom, either High voltages for tubes kind of things.
So i tried to mix a bit all of this, and came up with this :




(Just when i upload the image i spot a mistake : the input of LM317HV shouldnt see 18v, definitely more!)


I think i'd order a custom transformer with two 18V AC windings, each of them taking care of its own line.


So i finally write here to seek some help!

1/ Are there any better idea than this for my project?
2/ Do you know anyone who offers that kind of pcb? (its great to learn kicad, i love it.... but if i could buy a ready made and tested pcb, i'd be on the safe side!)
3/ Is my schematics allright?
4/ How is your day going so far?!

Thanks a lot if you read this, you are angels!!

Flo

 

[kags]

This is a single supply kit - definitely overkill for what you need, but you can see the building blocks and customize this design. Your needs are different, but this schematic may help you explore how to get the voltages you need from one transformer. JLM might have a more suitable supply that works off the shelf for you, but this schematic has been helpful to me in seeing how the building blocks go together.

http://www.jlmaudio.com/V6/V6 Schematic.pdf

 

[f.aiseur]

Hi Kags, thanks for this! i was indeed browsing JLM site, its one of those very valuable source for sure!

 

[f.aiseur]

So it seems that most of the psu offered by JLM are using doubler/tripler topology and, except if i’m missing something, they all can provide max 300/400mA, which isnt enough for me.
I just (re)found out about fivefish products and this one seems like a perfect match for my needs :

https://www.fivefishstudios.com/pdf/PSU2448PlusAssemblyGuide.pdf

So i might give it a try

 

[beatnik]

The fivefish also uses a doubler for the 48V rail

LM317 max current is 1.5A so it should meet your requirements, as long as power transformer is sized properly

 

[f.aiseur]

Hi beatnik,
Then i dont get where the doubler is on the fivefish. My understanding is that they take the 48v line out of the two secondary windings in serie..
And the +/- uses the center tap.

Where am i wrong?

Thanks!

 

[abbey road d enfer]

Hi beatnik,
Then i dont get where the doubler is on the fivefish. My understanding is that they take the 48v line out of the two secondary windings in serie..
And the +/- uses the center tap.

Where am i wrong?

Thanks!

I don't have the schemo, but the way you describe it, the negative of the 40V supply cannot be grounded with that of the +/-18V. I would think it's a problem.
The only simple answer is to use two separate transformers, one with a 2x18Vac secondary and one with a 32-36Vac.
Another possiblity is using isolated DC/DC converters that would take a single rectified voltage and convert to the desired voltages.

 

[f.aiseur]

Hi abbey, thanks for chiming in.

I also dont get this part from the schematics.
You can find it on the link posted above (https://www.fivefishstudios.com/pdf/PSU2448PlusAssemblyGuide.pdf), in the end of the pdf.

The other possibility you mention would be to have a "main" 40VDC rail, and two DC/DC converters to create the +/-18v?

 

[dogears]

the voltage doubler is formed by C6 and C7

 

[GJB17]

Hi... I have been doing some audio design of recent times and have used the PSU as per the attached. I won't go in to great detail at this point but it will supply all of +/- 15 (or more), and 48 volt (phantom) supplies. It broadly based on a Yamaha design and has worked well and reliably. It only needs a single transformer. I have also designed a PCB for it... using Kicad (since you mentioned it!

 

[GJB17]

Oops... the R4 value is not correct. I will check.

 

[MidnightArrakis]

Hi... I have been doing some audio design of recent times and have used the PSU as per the attached. I won't go in to great detail at this point but it will supply all of +/- 15 (or more), and 48 volt (phantom) supplies. It broadly based on a Yamaha design and has worked well and reliably. It only needs a single transformer. I have also designed a PCB for it... using Kicad (since you mentioned it!

>> HEY!!!.....GJB: If you don't mind.....could you share with me your KiCAD schematic and PCB files, as well as your output GERBER and N/C Drill files so I could review them for you? I have and use a "GERBER Analyzing & Editing" program that can detect -- fabrication and manufacturing -- errors that the PCB-design "DRC" checks can't catch!!! You can PM me with this information if you wish.

FYI: Here are a few examples of the types of PCB's that I have designed:







I'm just offering to help.....that's all!!!

/

 

[abbey road d enfer]

Hi abbey, thanks for chiming in.

I also dont get this part from the schematics.
You can find it on the link posted above (https://www.fivefishstudios.com/pdf/PSU2448PlusAssemblyGuide.pdf), in the end of the pdf.

It uses a doubler for producing phantom. Not a very good solution for producing 40V/1A.

The other possibility you mention would be to have a "main" 40VDC rail, and two DC/DC converters to create the +/-18v?

It's a possibility.

 

[GJB17]

My PCB's are way simpler than the ones you have posted... i.e. small double sided PCB's.
Nonetheless I am happy to share them with you. What would be the best way to get the files to you. Email would probably be easiest... or Dropbox... if you don't mind giving me that info.

 

[Voyager10]

It would help to know what sort of current (10mA? 100mA? 1A) the +/-18V circuits are expecting.

One idea to consider would be whether the +/-18V bits can be converted to single-supply operation, i.e. just +36V. This is obviously a good fit given an existing +40V supply. Do you have a schematic?

 

[GJB17]

Hmmm... splitting a single supply probably not a good idea. My circuit (below) needs only a single trani with the usual dual winding in any event

 

[GJB17]

Once you have had a look over I can provide a bit more description

 

[Voyager10]

Ah, sorry, I think we've got some wires crossed. I intended to ask @f.aiseur whether they had schematics for the +/-18V circuitry which was being added. It would give us an idea of the power requirements, and how easy it is to adapt to single-supply use.

Your (GJB's) circuit looks good, I think the sticking point was the need for one whole amp at 40V.

 

[f.aiseur]

It would help to know what sort of current (10mA? 100mA? 1A) the +/-18V circuits are expecting.

One idea to consider would be whether the +/-18V bits can be converted to single-supply operation, i.e. just +36V. This is obviously a good fit given an existing +40V supply. Do you have a schematic?

Hi Voyager!
I don't really know how much precisely, its just for two tiny VU meters and an isolator board (5xTL074)
So i'd say more in the 200/400mA ballparck.
And no schematics no, this is partly why i started this thread

 

[GJB17]

I have reviewed your schematic. A few observations.
I now see the need for a 40 V supply... as the majority of the circuitry is discrete components and of an older "style" designed to run on a single supply. Nowadays it would of course be (and is) built using Opamps using split supplies.... which is how you are going to configure the additional circuitry (VU meters and drivers, etc.) I assume?
Speaking of your +/- supply. I would change your rectifier system... it will only provide half-wave rectification which produces a lot more ripple (hum). Use an 18-0-18 transformer... and configure as per my schematic.
+/- 16 or even 18 volt power would not be critical in your app... so 15 volt (fixed) regulators could be used. No need for extra circuitry and adjustment.
I can't see a simple way to be able to use one transformer. A commercial product might (and often do) use a dual secondary transformer. You may be able to find one through Digikey or similar... but likely to be expensive! The only ones that I am aware of are large units for PA's which need separate high and low voltages for the PA and preamp stages.
I have looked at your PCB layout which seems fine thus far... and has the rats-nest... but does not yet include the actual tracking. That's the hard bit!