Precision +/-15V @ 1A PSU

Uncle Krunkus · Last edited by Uncle Krunkus on Fri Oct 10, 2008 4:28 am; edited 1 time in total

I'm working on a new precision +/-15V @ 1A PSU and I thought I'd share some pics and info on the process.
It's based on the LM723 (*2) regulator chip with MJE3055 transistors to carry the current load.
The schematic is freely available on the Elby Designs site. Here
I've done a stripboard layout of my own which I'll post if anyone is interested.

Please Note:
This DIY project involves the wiring of a mains transformer and associated IEC socket, fuse and switch. Attempting this without the proper precautions can be lethal!
If you have any doubts about your ability with mains potential wiring,... Do Not Attempt this Project.
No responsibility will be taken by myself or electro-music.com for anyone's ability or lack thereof to attempt a project of this nature.

I'll be posting some pics soon.

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

Thanks for reminding me of that one.

How easy would it be to pull out more amps? The MJE3055 can handle up to 10A so I guess the design is limiting in other places. I have some 2N3055 lying around that can do even more current.

fonik · Posted: Tue Sep 23, 2008 7:03 am Post subject:

the limitation is obviously the heat dissipation. take a look at these gorgeous heatsinks! Shocked

i thought about a 1.5A PSU using the units case itself as heatsink. thoughts?

frijitz

Peake · Posted: Tue Sep 23, 2008 9:11 am Post subject:

bugbrand · Posted: Tue Sep 23, 2008 10:37 am Post subject:

I've just started to use some POwer One HAA15s and these are LM723 based also with 2n3055s. These use the (semi-)case for heatsinking.

Uncle Krunkus · Posted: Tue Sep 23, 2008 2:59 pm Post subject:

I was going to elaborate on that.
This design will actually allow me to up the Amps later.
I'm putting in an 18-0-18 @ 4A4 per rail transformer.
Initially I'll use the 1A per rail circuit, but I'm also looking at a way of beefing up that circuit using a TIP29 and a 2N3055 on each rail. And yes, the trick is to fit the right heatsinking in. It should end up being able to deal with about 3A per rail.
Right from the start, I'm putting it all in a 2U rack case, and designing the layout with the upgrade in mind.
That's why I thought you guys might be interested. Wink

Sine · Joined: Sep 10, 2007 Posts: 111 Location: Netherlands

I have built this thing and it is really rock solid with minimal drift

The only change I made is using darlington transistors so the 723 doesn't have to supply as much base current, something like the TIP140 or BDV65 would do nicely, or a MJ3001 if you must have a TO-3 in there Wink

Uncle Krunkus · Posted: Tue Sep 23, 2008 4:24 pm Post subject:

That's one of the reasons for going with the TIP29/2N3055. I'm going to do them as a discrete darlington pair.

Uncle Krunkus · Posted: Sat Sep 27, 2008 5:15 am Post subject:

Okay,
Here's the first pic.
These are all the basic parts, laid out roughly where I want them. You can see the start of my distribution panel bottom right (it's come a long way since then!)
I think there should be plenty of space for expansion later, like I said, that transformer can supply 4A4 on each rail, so to up the ante I only need to come up with a new stripboard layout and heatsink pair later on.

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Uncle Krunkus · Posted: Sat Sep 27, 2008 5:22 am Post subject:

Next,
I got to work on the back panel. Here's a pic of the panel, with holes cut for the IEC power socket and fuse holder. There's a collection of tools around it which I use for this kind of work.

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Uncle Krunkus · Posted: Sat Sep 27, 2008 5:46 am Post subject:

Two shots of the power socket and fuse holder. Note the lug for attaching the chassis earth. Check with a meter that there is 0R from the lug to the other end of the panel. Wink

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fluxmonkey · Joined: Jun 24, 2005 Posts: 708 Location: cleve

i cant tell from the pics what kind of ventilation scheme you're using? big heatsinks help conduct the heat away from the regulators, but it's still got to have someplace to go... vent holes and/or forced air.

Sine · Joined: Sep 10, 2007 Posts: 111 Location: Netherlands

Great work on the case Krunkus,

Yes, a step drill is a MUST for anyone that does diy electronics.

I build mine on matrix board

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.

Originally for +-12V, but later modules needed +-15V so I did a "upgrade" on it a few months later Wink

Uncle Krunkus · Posted: Sat Sep 27, 2008 7:58 am Post subject:

Uncle Krunkus · Posted: Sat Sep 27, 2008 8:03 am Post subject:

I don't want to cut holes at the moment, 'cos I don't know where the larger heatsinks will be mounted. I've never built a PSU this size before, so I want to do a bit of testing under load and find out just how hot it gets. Very Happy

Sine · Joined: Sep 10, 2007 Posts: 111 Location: Netherlands

Personally I would ( and I have on my version ) mount the heatsinks on the back of the unit.

Uncle Krunkus · Posted: Sat Sep 27, 2008 5:44 pm Post subject:

Here's the distribution board.
I used stripboard, as I'm going with the .1" pitch molex style keyed headers and plugs.
The screw terminals are reverse mounted, and jumpered over with a piece of .7mm tinned solid copper wire. I continued this along the stripboard to maintain the cross section and keep the resistance as low as possible. I thought about adding an extra 2 caps at the other end of the distribution board, but decided that would be overkill and would just up the inrush current. What do you guys think? I could still add them later if needed.

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Uncle Krunkus · Posted: Sat Sep 27, 2008 5:48 pm Post subject:

Then I mounted it in the slot with 6mm threaded plastic spacers. These are great, as they eliminate the "now, just hold on to those 5 things while I get this one in place,....doh!" effect. Laughing

8 mounting points might seem a bit much, but it wasn't much harder than 4, and it means the board won't flex at all when connecting/disconnecting plugs.
I also kept it to one half of the panel depth, so I can add a second one later if need be.

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blue hell · Posted: Sat Sep 27, 2008 6:22 pm Post subject:

Uncle Krunkus · Posted: Sat Sep 27, 2008 7:54 pm Post subject:

bugbrand · Posted: Sun Sep 28, 2008 5:09 am Post subject:

Uncle K -- good work on the rectangular holes --- nice and tidy!!

Uncle Krunkus · Posted: Sun Sep 28, 2008 6:03 am Post subject:

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

stipboard layout available andy?

Uncle Krunkus · Posted: Wed Oct 01, 2008 6:02 pm Post subject:

Yeah,
Hold on, I'll just tidy it up a bit. Very Happy