5V 3A PSU

Currently in development in my workshop is a new power supply. It is a 5 volt 3 amp unit and because it is single voltage and uses a proper transformer, it is not legal to sell it in the European single market or in some states in the US (and maybe Australia?).

Actually that just spoiled my intro, realising that you could only benefit by it by buying it on the sly. But anyway, if you look up my surname (Slee) you should find it's a derivation of sly...

How could you benefit by it? Good question: one of our senior members reckons he will benefit by it because he instigated the process - namely msphil (hi Phil!). He wants it for his Squeezebox Touch, and on hearing about this another senior member (Fatmangolf) became interested (there, I spilled the beans... )

I must admit that this has been on my pile of things to do since 2015, and poor old Phil must be losing patience by now () and so to restore his faith I decided to write about its progress here.

Yesterday I did all the workings out and ordered up the remaining parts required. What took longer than I thought was working out a little extra feature I consider essential for a 5V supply...

Logic/digital chips run on 5V (and some on 3.3V), and it would seem like many devices, this might not use any intermediate regulation (other than if 3.3V is required) and relies on the 5V from its supply being a good stable 5V.

If you were to try supplying a 5V circuit from say a 12V supply what would happen? Well, if the device has no overvoltage detection built-in, it would break!

One good thing about the EU, is it thought about things like this, and legislated on it, but in an abstract way. Now, in Yorkshire we have a reputation of calling a ***** a ***** (political correctness prevents me from using the actual word here).

Because of the abstract way the legislation is formed, manufacturers of such devices may not have understood what it means, and so I have to assume they didn't, and put into the power supply what they may not have done at their end.

And that is overvoltage protection such that if part of the power supply failed and decided to output more than 5V, it will shut down and prevent catastrophic destruction of the device it is powering.

When making power supplies for ones own products this is not an issue, but making an aftermarket power supply one needs to think about such things.

Anyway, after much frustration (the world seems to be getting that way these days) I was able to find/decipher what I was looking for in the form of a chip and external MOSFET required to perform the action.

So, it should comply in that respect, but it is still against legislation to actually sell it. However, by providing another output voltage, it becomes legal. And because nobody actually wants another output voltage - they just want the 5V - we can make that voltage anything we want, and it makes sense to use a voltage which appears somewhere in the circuit. And so I will designate a pin on the output connector as one of those. Hey presto! It then complies!

More on its progress shortly.

This PSU could be an upgrade for Raspberry Pi users as well. The Digi + Pro and DAC+ Pro convertor boards for the RPi need 5V and 3.3V supplies. If this is within the scope, then would you please add me to the list for a unit.
I have previously LM723N based regulators with BD140 as "output" device for (higher) current capability. These sounded quite good, but didn't have the benefit of professional design and measurement, which I'm sure your PSU will benefit from and therefore be a significant improvement.

Graham Slee wrote: A regulator is a regulator is a regulator... Will my choice sound better? I would doubt that. What does make a difference however, is the layout: the grounding regime and the charging current lengths and impedances of path. Let's hope I get that bit right...

Add to the layout considerations the choice of the most appropriate components, then you have the reason why your design might well sound better.

I'll watch with interest how this develops and ultimately hope to benefit with a new PSU.

5V 2.5A + 3.3V 500mA would suit my needs, don't know what others may need.