Would you like to see an AC mains DIY PSU design tutorial?

MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

I will be buying the components for a new dual polarity, mains powered linear PSU within the next few days, once a few other details have come to pass. This will be for my synth experiments.

Despite their obvious importance, then in my experience the design and building of linear PSUs tend to be one of the gray areas of electronics DIY. As such I was wondering if people here at E-M would like to see a 'Build-Along' of sorts? Many of the general rules of thumb on this subject you tend to find are actually not that great, and as a result many people end up with problems of various sorts when they build their own PSU(s).

Personally, when building something like this, I like to know what the rules actually are. Doing so then gives me the option to decide whether I actually want to follow them to the letter, or when I can cut some corners.

Did you know that:

There is such a thing as having too large a heat sink?
The data on many heat sinks are not to be taken literally?
Usually there is one optimal size for a smoothing capacitor - yet few books for electronics hobbyists will tell you how to find it?
Your mains transformer is probably too small?
There are important differences between the families of three legged voltage regulators - which is also why their prices varies considerably?
The square root of two (1.41421356...) has very little relevance to real world PSU design?
At least one transformer manufacturer doesn't know how to use their own products? (*Very* reassuring that is... )
It is possible to design a linear PSU for higher - though perhaps not 'high' - efficiency?

If you answered 'No' to one or more of these questions, then you might want to consider letting me abuse the Queen's English in an attempt to explain these and many other fine points in the art of designing linear power supplies (How is that for a run-out sentence? Wink

)

Please vote according to conscience and your personal preferences.

- Frank.

kkissinger · Posted: Tue Jan 03, 2012 10:12 am Post subject:

Please include fusing guidelines, too.

I have built the MFOS power supplies and they are very good. However, I had to make a "guestimate" on the transformer size.

This is an excellent idea -- might want to review safety tips/warnings for working with lethal voltage, too.

Paradigm X · Posted: Tue Jan 03, 2012 10:41 am Post subject:

Yes ! Im literally about to start, having put it off for 6 months due to concerns about safety.

JingleJoe · Posted: Tue Jan 03, 2012 10:59 am Post subject:

MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

Dougster · Joined: Sep 20, 2005 Posts: 272 Location: Tucson, AZ, USA

I had been toying with not replying to this thread, since I don't wish to give you any more relevance.

What is the purpose of this poll other than to draw attention to yourself?

In other words, as we merkans say, "put up or shut up."

Regards,
Doug

EDIT: To the casual reader, sorry about the snarkiness. Please read the copyright thread for background info.

Mooger5 · Posted: Tue Jan 03, 2012 12:24 pm Post subject:

Interesting! Are we talking regulated or non-regulated?
The most complex power supply I´ve built was for a valve amp. I used Duncanamp´s PSU Designer to predict the ripple after a long chain of RC filters.
Building a better power supply may not be these users´priority; most will be happy with one that doesn´t hum, IMHO. But from my Hi-Fi background I have this notion that regulated is "essencial" but non-regulated just sounds "better". So, why not use two seperate PSUs, one regulated for CV and other critical functions and one non-regulated for the audio path?

EdisonRex · Posted: Tue Jan 03, 2012 5:07 pm Post subject:

I'd suggest that you publish what you want to, as people here are able to cross verify what you publish with what else we know. I've been a proponent of overrating power supplies for a while, but there's plenty that can be said in the exposition.

Paradigm X · Posted: Sat Jan 14, 2012 11:56 am Post subject:

So is this happening then or not? Confused

Cheers

blue hell · Posted: Sat Jan 14, 2012 12:12 pm Post subject:

I'm afraid that some reactions to MadScientist (in another thread mainly) may have led him to believe that this community is not always as friendly as it could be ... this whole situation is a bit disappointing Crying or Very sad

Anyway, so I'm afraid this will not happen.

Dougster · Joined: Sep 20, 2005 Posts: 272 Location: Tucson, AZ, USA

Not so fast, don't give up yet....

Regards,
Doug (he says mysteriously...)

LFLab · Posted: Sat Jan 14, 2012 1:21 pm Post subject:

elektro80 · Posted: Sat Jan 14, 2012 1:50 pm Post subject:

Frank will be back. I've communicated a bit with him.

Dave Kendall · Posted: Sat Jan 14, 2012 4:47 pm Post subject:

Hi.

+1 for some info here on PSU design, if you're up for doing it Frank. Thanks, it's a cool offer. Smile

I'm another one who's shied away from home-built PSUs so far .....

Something I'd be *very* interested in, is discussion/details of the sort of protection/short circuit circuitry you get on a Power-One HAA15 (mine's a MOTM 900). If you connect it the wrong way around, it just seems to shut off.
I've powered up the modular with +15V and -15V inadvertently connected the wrong way around to a new module a couple of times, and nothing happened. No power, no magic smoke. I would love to know how that works....

Info about building a "bomb-proof" power supply, that protected modules too would be a very popular thing for SDIYers I reckon.....

cheers,
Dave

PS, I know it's Friday night (beers an all....) but has anyone else noticed that Dougster and EdisonRex's avatars are almost identical except for the background and some moustacheness?

Have they ever been seen together in the same room?

Is there a secret SDIY person cloning facility somewhere, perhaps on Kamino?

(OK, I'm going now..... Wink

)

Dougster · Joined: Sep 20, 2005 Posts: 272 Location: Tucson, AZ, USA

Dave Kendall · Posted: Sat Jan 14, 2012 5:18 pm Post subject:

Hi Doug.

Most of my stuff is EFM or CGS, apart from a Paia MIDI2CV8, and my own MIDI2CLOCK. None of the modules have protection diodes, and they all have ferrite beads rather than 10-22ohm resitors in series with the power rails (ferrite beads have been retro-fitted along with 10uF caps to the EFM stuff.)
That's why I'm puzzled/intruiged by the HAA15... By all rights I should have generated some Magic Smoke by now with the odd reverse polarity hookup....

cheers,
Dave

Dougster · Joined: Sep 20, 2005 Posts: 272 Location: Tucson, AZ, USA

Dougster · Joined: Sep 20, 2005 Posts: 272 Location: Tucson, AZ, USA

MadScientist · Joined: Nov 28, 2011 Posts: 63 Location: Denmark

LFLab · Posted: Sun Jan 15, 2012 2:04 am Post subject:

apart from dimensioning of the psu, this thread is also a good place for other stuff like output protection and simultaneous shutdown and startup. had to put in some new discretes when one rail dropped out a while back. i have schematic somewhere i'll post it when i'm on my pc later on.

sizone · Posted: Sun Jan 15, 2012 3:31 am Post subject:

I, for one, would love to see you go ahead with this. It seems, no matter how hard I try, I always end up with +11.7v and -11.9v and I would at least like to know why.

LFLab · Posted: Sun Jan 15, 2012 3:57 am Post subject:

There could be other reasons, but if you are using a regulated supply, it is necessary to hook up a load resistor before measuring the voltage, especially the 79xx series is noted for not being able to regulate properly if it is not delivering any current.

By the way, this is the simultaneous shutdown trick:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

It's from a soundcraft psu, uses a positive regulator for both rails, and shuts down both if one is shorted. Not sure how critical the type of the transistors are, not very, I think (2SA and 2SC are not easy to get overhere, at least not all types).

LM338 is a 5A regulator, think you can do this with LM317 as well. Not sure if 78xx lends itself to the same trick.

Dave Kendall · Posted: Sun Jan 15, 2012 8:00 am Post subject:

Jarno - thanks for that diagram. Seems simple enough, and the +48V section looks like it could be easily discarded if not needed. Tweaking the circuit for ±15 shouldn't be too hard.....

Doug - the sig is a quote from Bishop, the android or "Artificial Person" as he prefers to be called, in the movie Aliens. Wink

cheers,
Dave

Dougster · Joined: Sep 20, 2005 Posts: 272 Location: Tucson, AZ, USA

EdisonRex · Posted: Sun Jan 15, 2012 8:32 am Post subject: