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Old 30th Oct 2021, 5:43 pm   #1
Wendymott
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Default DC Power Supply Unit.

Hi peeps...... Most of my home brew test equipment and some bought items are low voltage devices. Most are 12V DC and low current, thus "wall warts" were used, however we all know these can be a source of RF interference, therefore... a rainy friday and saturday, I decided..it was time to tidy up, and make a multi DC voltage source, with an IRON transformer..
There are 4 12V DC and one 5V DC rated at 500 m/A. This covers most requirements.
I am not showing the "internals as the pcb was "hacked a bit" and its not pretty.. However a MK 2 PCB is designed for retro fitting if required.
The regulators are 7812 1A and 7805 1A, mounted on a heatsink. The unregulated DC is 18V. Each output has a separate regulator.
The case is a "recycled" Vero case about 20 years old.
In one "fell swoop" I have reduced the wallwart count and tidied the back of the bench up.
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Old 30th Oct 2021, 7:01 pm   #2
Cruisin Marine
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Default Re: DC Power Supply Unit.

I would make a second supply with +5, -5 and +15 -15 for op-amps and CMOS at full volts if need be.

Nice work Wendy, as always.
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Old 30th Oct 2021, 7:05 pm   #3
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Default Re: DC Power Supply Unit.

I prefer linear power supplies. Do your 5 power supplies share a common negative rail?

It could cause problems if you connect old germanium PNP circuits with modern circuits.

Those 'wall warts' provided galvanic isolation.
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Old 31st Oct 2021, 1:58 pm   #4
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Default Re: DC Power Supply Unit.

Hi Peeps..... All suggestions noted. I have no need for + / - rails as this is intended solely to replace wallwarts, I already have lab supplies that can supply various variable voltages. The psu shares a common - rail ..... as above. If I needed another neg supply for germanium stuff, it would be supplied separately. See above statement.
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Old 31st Oct 2021, 2:21 pm   #5
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Default Re: DC Power Supply Unit.

I can see tears at bedtime here, plugging the 5V into 12V.
 
Old 31st Oct 2021, 3:44 pm   #6
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Default Re: DC Power Supply Unit.

I would have put a little diagram on the PSU label making clear whether the pins or barrels of the outputs were positive.

David
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Old 31st Oct 2021, 3:54 pm   #7
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Default Re: DC Power Supply Unit.

Nit-picking, I know, but 'm/A' doesn't make sense. It literally means 'millis per amp'.

'mA' means milliamps.
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Old 31st Oct 2021, 7:14 pm   #8
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Default Re: DC Power Supply Unit.

Quote:
Originally Posted by merlinmaxwell View Post
I can see tears at bedtime here, plugging the 5V into 12V.
Obviously it's built now (and very neat it looks too) but it might have been better to use different, incompatible connectors for 5V and 12V. Maybe something to consider for the MkII version.
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Old 31st Oct 2021, 8:13 pm   #9
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Default Re: DC Power Supply Unit.

Quote:
but it might have been better to use different, incompatible connectors for 5V and 12V.
I would use terminals, at least you have to think about which wire goes and to where.
 
Old 2nd Nov 2021, 12:42 pm   #10
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Default Re: DC Power Supply Unit.

Hi Peeps. All noted.... As its only ME using it.. I know.. its centre pin +ve. Also the +5 could be a different size.... maybe a GOOD idea. m/A or mA my "nits have been picked" .
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Old 2nd Nov 2021, 12:53 pm   #11
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Default Re: DC Power Supply Unit.

Quote:
Originally Posted by Wendymott View Post
As its only ME using it..
And after a goof, you'll criticise yourself harder than you'd ever let anyone else do so.

David
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Old 3rd Nov 2021, 1:36 pm   #12
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Default Re: DC Power Supply Unit.

Hi peeps.... MK.2 or should that be.. MARK 2 or "II" as in romans ?
New pcb, New front panel..... new label.
Works just as good as the MK 1.....
As this one is more tidy, or... tidyer I thought you could see the innards.
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Old 3rd Nov 2021, 3:49 pm   #13
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Default Re: DC Power Supply Unit.

MkII looks nice, I would use a different colour LED for the 5v o/p though.
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Old 3rd Nov 2021, 3:54 pm   #14
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Default Re: DC Power Supply Unit.

Very neat construction - puts my efforts to shame.
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Old 3rd Nov 2021, 5:28 pm   #15
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Default Re: DC Power Supply Unit.

I do like "WENMO", my name is so unlinked to anything fun I use "ACME" for the under the bench test kit I make at work, and of course the "ACME Volt-O-Test" style too. It is fun, engineering should/must be so, and people remember.
 
Old 3rd Nov 2021, 6:41 pm   #16
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Default Re: DC Power Supply Unit.

Very nice, Wendy! How do you do the PCB? It's admirably neat and even. Is it a plain sheet of paxolin with point-to-point underneath, or do you etch and drill your own?

I agree, merlinmaxwell. I have some various brass plates from my grandfather I put on home-made constructions. Looking around, my 300B amplifier proudly sports a raised and painted "Shand, Mason & Co. Engineers, London" from a very superior coat rack, and I've got a plaque from a mattress manufacturer on my ESR meter...
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Old 4th Nov 2021, 12:27 am   #17
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Default Re: DC Power Supply Unit.

It looks a nice unit Wendy. Personally I would put the fuse before the mains switch and add a plastic cap to the toggle switch for safety incase the internal insulation in the switch broke down and the body went Live.

David
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Old 4th Nov 2021, 12:29 am   #18
Wendymott
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Default Re: DC Power Supply Unit.

Merlin.. I coined the name as Denmo, years ago, but changed it due to my personal circumstances. Unc "B".. Re the pcb......I have reasonably perfected the Toner / Hot Iron method, none of this Film etc....for me. If I have to make complicated tight geometry pcb's I go to PCBWAY in China. As a "tight" yorkshire person, to reduce the amount of copper loss and etch contamination when etching, I coat any excess perimeters, with nail varnish, I also use thick tracks and lots of ground plane.
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Old 4th Nov 2021, 12:55 am   #19
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Default Re: DC Power Supply Unit.

.
Congratulations on your project.
.
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Old 4th Nov 2021, 6:24 pm   #20
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Default Re: DC Power Supply Unit.

Wenmo, Denmo, both super monikers. At work we now have a "Branding Consultant", I will leave it as that!!!!
 
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