Rail-splitting a wall wart

On Sun, 5 Feb 2023 21:11:11 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

>John Larkin wrote:
>
>------------------------------
>> https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1
>
>
>** Using a AC ( transformer) wall wart has a few notable advantages it you are going to use linear regs.
>
>One with a single 12 volt secondary will supply +/-  16VDC or so using a ( 2 cap, 2 diode) voltage doubler. 
>Highly reliable, no SMPS noise, very safe mains isolation.
>
>
>....  Phil

Ac warts aren't common any more. We do try to design units that will
work, or at least not blow up, when someone grabs the wrong cord off
the tangle on the bench and plugs it into our box.

+24DC is our default input. A box might not work at 12, but at least
won't blow up. Warts above 24 are uncommon.

I guess eventually everything will be USB-C with smart voltage
selection. But still positive only.

I guess a USB-C power source is not generally isolated. Maybe never?

mandag den 6. februar 2023 kl. 05.43.40 UTC+1 skrev John Larkin:
> https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1

https://imgur.com/NhlLGGc

On Monday, February 6, 2023 at 12:56:04 PM UTC-5, lang...@fonz.dk wrote:
> mandag den 6. februar 2023 kl. 05.43.40 UTC+1 skrev John Larkin: 
> > https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1 
> 
> https://imgur.com/NhlLGGc

April Fool's ?

On Mon, 6 Feb 2023 09:56:00 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>mandag den 6. februar 2023 kl. 05.43.40 UTC+1 skrev John Larkin:
>> https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1
>
>https://imgur.com/NhlLGGc

Similar idea, namely that a splitter before the regulators can be
sloppy, with a reasonable deadband. 

On Mon, 6 Feb 2023 10:00:30 -0800 (PST), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

>On Monday, February 6, 2023 at 12:56:04 PM UTC-5, lang...@fonz.dk wrote:
>> mandag den 6. februar 2023 kl. 05.43.40 UTC+1 skrev John Larkin: 
>> > https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1 
>> 
>> https://imgur.com/NhlLGGc
>
>April Fool's ?

I thought of that one too. It's reasonable in some cases.

https://www.dropbox.com/s/v60roo6akcvncoj/Rail_Splitter_C.jpg?raw=1

but the zeners have other virtues.

Why don't you design a rail splitter and post it for discussion?

On Monday, February 6, 2023 at 7:27:11 AM UTC-8, John Larkin wrote:
> On Sun, 5 Feb 2023 21:11:11 -0800 (PST), Phil Allison 
> <palli...@gmail.com> wrote: 

> >** Using a AC ( transformer) wall wart has a few notable advantages it you are going to use linear regs. 
> > 
> >One with a single 12 volt secondary will supply +/- 16VDC or so using a ( 2 cap, 2 diode) voltage doubler. 
> >Highly reliable, no SMPS noise, very safe mains isolation. 

> Ac warts aren't common any more. 
...
> +24DC is our default input. A box might not work at 12, but at least 
> won't blow up. Warts above 24 are uncommon. 

The 'common' AC wart at 9VAC was ideal for an external modem (remember those?)
in the '90s, but today it's 19.5VDC for a laptop.   If you want to futurize, that might be the
pattern to work to.

One (ASUS, if it matters) adapter here is 19V 2.37A from 100-240VAC input,
in a 2.0 x 2.0 x 1.125 inch package, and next year's model will be 
an improvement on that, though I can't imagine how.

Maybe a 50 kHz 20 VAC sinewave?   Nah, I'd generate harmonics with
any attempt to rectify.   Better to keep those in the distal end of the power lead.

On Monday, 6 February 2023 at 15:27:11 UTC, John Larkin wrote:
> On Sun, 5 Feb 2023 21:11:11 -0800 (PST), Phil Allison 
> <palli...@gmail.com> wrote: 
> 
> >John Larkin wrote: 
> > 
> >------------------------------ 
> >> https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1 
> > 
> > 
> >** Using a AC ( transformer) wall wart has a few notable advantages it you are going to use linear regs. 
> > 
> >One with a single 12 volt secondary will supply +/- 16VDC or so using a ( 2 cap, 2 diode) voltage doubler. 
> >Highly reliable, no SMPS noise, very safe mains isolation. 
> > 
> > 
> >.... Phil
> Ac warts aren't common any more. We do try to design units that will 
> work, or at least not blow up, when someone grabs the wrong cord off 
> the tangle on the bench and plugs it into our box. 
> 
> +24DC is our default input. A box might not work at 12, but at least 
> won't blow up. Warts above 24 are uncommon. 

Not any more.  I have a few 48V and 54V power bricks used for PoE and PoE++
respectively.

> I guess eventually everything will be USB-C with smart voltage 
> selection. But still positive only. 

The trouble with that is that the standard requires the negotiated output to be
less than or equal to the requested output, so you need to check whether you
actually got what you asked for.

> I guess a USB-C power source is not generally isolated. Maybe never?

Its isolated if it is a wall-wart, but not if its part of a PC.
John

Fred Bloggs wrote:
> lang...@fonz.dk wrote:
>> skrev John Larkin:
>> > https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1
>>
>> https://imgur.com/NhlLGGc
>
> April Fool's ?

A vivisectioned, so to speak, Sijosae rail splitter?

Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

On 2/6/2023 2:05 PM, John Larkin wrote:
> On Mon, 6 Feb 2023 10:00:30 -0800 (PST), Fred Bloggs
> <bloggs.fredbloggs.fred@gmail.com> wrote:
> 
>> On Monday, February 6, 2023 at 12:56:04 PM UTC-5, lang...@fonz.dk wrote:
>>> mandag den 6. februar 2023 kl. 05.43.40 UTC+1 skrev John Larkin:
>>>> https://www.dropbox.com/s/e6okuzog0nulvjm/Rail_Splitter_B.jpg?raw=1
>>>
>>> https://imgur.com/NhlLGGc
>>
>> April Fool's ?
> 
> I thought of that one too. It's reasonable in some cases.
> 
> https://www.dropbox.com/s/v60roo6akcvncoj/Rail_Splitter_C.jpg?raw=1
> 
> but the zeners have other virtues.
> 
> Why don't you design a rail splitter and post it for discussion?
> 

LT1166 for the cash-flush, LM386 for the cash-strapped.

On 2/6/2023 8:30 AM, Don wrote:
> whit3rd wrote:
>> upsid...@downunder.com wrote:
>>
>>> Using an AC wall wart 50/60 Hz iron core transformer with special
>>> connector will discourage many experimenters and their devices will
>>> not work with AC, possibly releasing some smoke :-)
>>
>> An AC connector can be unpolarized, but no DC connector commonly is.
>> So, you can fit an AC wart with reversible plug, and no DC wallwart is
>> likely to be compatible.
>> I've got a subwoofer that takes AC/DC input, it has a DC-like connector
>> and full wave bridge... can't get the polarity wrong either.
> 
> Even when the voltage and power matches, it can be difficult to find a
> compatible connector. This thirty-four assortment of different sizes and
> shapes to connect a nominal 19.5VDC adapter to a laptop fails to cover
> all possible variances:
> 
> <https://www.ebay.com/itm/314035139187>
> 
> Danke,
> 

I have one of these older Radio Shack aftermarket laptop power bricks, 
the only laptop I've ever owned in recent history that any of the 
included connectors fit is a 2016 Fujitsu Lifebook.

<https://www.reallytech.net/catalog/product/view/id/16907/s/radioshack-2730853-laptop-power-supply/>