Re: more X-rays Silvertel PoE Supply

"Arie de Muijnck" <noreply@ademu.nl> wrote in message news:nnd$7f138845$4f992b3a@6f6ac280155cacc4...

On 2024-10-02 20:02, Edward Rawde wrote:

"Don Y" <blockedofcourse@foo.invalid> wrote in message news:vdjvmh$3aipj$1@dont-email.me...

On 10/2/2024 8:46 AM, Edward Rawde wrote:

I did PoE with LTC4267 some years ago such that 12V could also be supplied from a wart.
Fully isolated with a PA1138 transformer.

>
How did you inform the PD of the fact that it was no longer
dependant on (and controllable by) the PSE?  Or, did you forego
in-band reconfiguration and power control?

>
It wasn't necessary for the fairly specialized product which was configured at install time with power from PoE or wart but not
both.
I seem to recall at least one accidental connection of both with no detrimental effect but it wasn't investigated further.

>
>
I've seen a problem when the PoE module had a TL431 + optocoupler at it's output as feedback circuit.
A limiting resistor was lacking, and +12.3V from a wart turned the TL431 fully on and destroyed the optocoupler.
Subsequent PoE operation then had an open loop and destroyed the supplied circuit.

I'd probably include an additional schottky diode to protect the TLV431, assuming the small power loss is acceptable.
Also a schottky in series with the wart power.
And maybe a FET to turn on a light load for the PoE when wart power is present.

>
Arie