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5V 3A PSU

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Ash View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2020 at 8:18pm
If 12V can't be accommodated, it's okay. Just getting rid of all the fans should be an improvement and I will stick with the stock PSU, which is also fanless and as it is sealed compared to many PC supplies, I shouldn't hear anything like coil whine. 

But if you are able to provide an experimental 12V linear supply in any form, regardless of how utilitarian and massively heatsinked it would have to be, I would be happy to try it, as long as it isn't £3k... I don't need any bells and whistles and don't mind it looking like a crude prototype. As long as it is sensibly constructed, safe to use and has some notes with it for guidance on its use, I am happy to play with it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2020 at 11:42pm
Taking a quick look online at "12V linear power supply", there appear to be quite a few products from China following the general transformer-rectifier-filter-regulator schematic but in cases with very little heatsinking... They must run burning hot and have short lifespans...

I know you would disapprove of selling me the PSU parts for 12V 3A without a case because mains voltage is involved and I have inadequate education/experience to not make a mistake with it. But with your extensive counsel regarding appropriate heatsinking and common sense safety during handling, I would consider it. Gotta be a safer option than buying a Chinese linear supply, which could have an entire list of safety issues...

We could discuss the necessary calculations, hazards and heatsink config best for adequate passive heat dissipation.


Edited by Ash - 02 Jun 2020 at 11:47pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2020 at 10:10pm
Originally posted by Ernie Ernie wrote:

Hi Graham,
So what can be done with a switch mode supply to clean it up?


The usual cure is a series 100uH inductor then a 1uF multilayer ceramic to deck.

Although it filters out the harmonic garbage, there isn't a very nice ground return path for the audio frequency range, and the smaller the signal by comparison, the worse it can sound.

They're not bad for power amps however, and that's because the regulation can "disguise" the LF ground return performance, by making for a more "solid" bass.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2020 at 10:11pm
Originally posted by Ash Ash wrote:

We could discuss the necessary calculations, hazards and heatsink config best for adequate passive heat dissipation.


Quite happy to do so. Probably best to do it here, stage by stage.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2020 at 10:38pm
Thanks Graham. I am waiting for the PC to arrive then I will use its stock 12V for a while and see what kind of sound I can get out of it. The design seems to be quite power efficient and as I won't have huge numbers of peripherals attached, it shouldn't draw too much current from the supply.

At some point in the future, you can invoice me for your PSU circuit/PCB design altered for 12V and let's just say 3A, for now. I can't see my PC needing to draw more current than that. I'm happy to pay you for your time if we go through a suitable enclosure design together. It will need to be stupid-proof in terms of earthing and thermals so there is no chance of me electrocuting myself or burning down my house. I won't be putting it anywhere near a mains socket until showing you photographs and receiving your approval.

Many years ago, I shocked myself on a small camera bulb/tube charging circuit. I still remember how much it hurt. That was just finite DC from energy stored in a capacitor, let alone AC from a continuous supply.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jun 2020 at 9:18am
On the subject of capacitor discharge, you want the circuit to fulfil that function, and not you.

The difficulty is retaining sufficient charge for the circuit, but reducing that charge to zero, quickly, after switching off.

The answer is obviously a resistor placed across the capacitor(s). A small value consumes the charge, and increases ripple voltage, but worse, ripple current too. A large value takes a long time to drain the capacitors. The small value dissipates more power and must be suitably power rated, meaning large.

However, provided this is a regulated supply, the leaky discharge can be through the regulator circuit, it will take a long time to go down, but touching the regulated output, won't lead to a "belt".

Also, realise that any filtering on the mains input involves capacitors, and although these, being relatively small, and losing charge quicker, if there is nowhere for that charge to go, it will remain across the exposed IEC inlet pins. Best to use a commercial mains inlet filter.

So, that was lesson one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jun 2020 at 7:56pm
Well when I get around to plugging it into the mains, I will be handling it like it's a bomb. No metal screwdrivers, no touching PCB tracks etc. One arm behind back, as an extreme example. I'm more concerned about inadequate heatsinking causing component damage.

Don't large capacitance reservoir capacitors have better voltage stability? Essentially the dilation of the exponential discharge curve on the time axis??
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