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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: more X-rays  Silvertel PoE Supply
Date: Wed, 2 Oct 2024 19:02:33 -0400
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"john larkin" <jl@glen--canyon.com> wrote in message news:kgirfj1614cfkvknad7dl2igqcb2qi5tq7@4ax.com...
> On Wed, 2 Oct 2024 17:00:52 -0400, "Edward Rawde"
> <invalid@invalid.invalid> wrote:
>
>>"john larkin" <jl@glen--canyon.com> wrote in message news:kqbrfjhrd5oto8ud8vm0395p6oo8eipige@4ax.com...
>>> On Wed, 2 Oct 2024 11:46:21 -0400, "Edward Rawde"
>>> <invalid@invalid.invalid> wrote:
>>>
>>>>"john larkin" <JL@gct.com> wrote in message news:v6mqfjd93ib6q8j7d7ontsaouidieh5b2u@4ax.com...
>>>>> On Wed, 02 Oct 2024 06:22:43 GMT, Jan Panteltje <alien@comet.invalid>
>>>>> wrote:
>>>>>
>>>>>>On a sunny day (Tue, 01 Oct 2024 14:16:09 -0700) it happened john larkin
>>>>>><jl@glen--canyon.com> wrote in <tipofjdtie76lbtd7lc2ger5uo7sglq3p5@4ax.com>:
>>>>>>
>>>>>>>
>>>>>>>https://www.dropbox.com/scl/fo/s6wfz2xtdyd6tv32tq3fp/AET6J4oF84HG2hJMeST6F-E?rlkey=acyvuv4z0h2kg0x97azbed8uo&dl=0
>>>>>>
>>>>>>Cannot make out much from those x-rays, pictures are better...
>>>>>>you can probably see the traces just like that?
>>>>>
>>>>> The x-rays are fun, but are admittedly more useful for an opaque
>>>>> potted module or an IC or discrete semi. I can prety well trace the
>>>>> Silvertel without them.
>>>>>
>>>>> I have a gigantic scary Carribean guy who does the xrays and I wanted
>>>>> an excuse for taking him to lunch, which turned into an interesting
>>>>> hike around The Bernal Cut. He trashed the xray system software, and
>>>>> had to rebuild it, and now it can do movies, which is great.
>>>>>
>>>>> I'd like to have some products that can be powered by PoE or a wart,
>>>>> and may want to put two 24-volt PoE supplies in series to get 48, so I
>>>>> need to understand how they work. The xrays just help a bit.
>>>>
>>>>If Ag9900 just works then why would you care how?
>>>
>>> Can I overpower it with a wart? Does that need another diode?
>>
>>Maybe. See other discussion in this thread.
>>
>>>
>>> Can I run two 24v Silvertels in series to get 48?
>>
>>I don't see why not since the data sheet says isolated.
>>It shouldn't be hard to verify that.
>
> Batteries are isolated, but a series string can destroy one cell by
> back-biasing it.
>
> Some power supplies will latch up, or not start up, in series with
> others. Lots of suplies won't start (and may fail) if their input is
> pulled negative.
>
> As the number of items in a design increases, the probability of some
> stupid error approaches unity. It's usually time efficient to be super
> careful, as opposed to spinning a few PCB revs.
>

Why do you need 48V ?

One of these will produce 48V or near enough, but not isolated of course.

https://www.ti.com/lit/gpn/TPS2375

I've just finished simulating a 12V 13W converter using an LTC4267 and 12V wall wart (simulated as 12V with series schottky) with 
automatic changeover between PoE and wall wart, whichever is avaiable. If both are available, PoE is used.

Making it 48V shouldn't be hard, but may require a custom transformer.

Would be nice to have a simulation model of MP8017.