Electronic – Help identifying MOSFET manufacturer

AOU438L from Alpha Omega semiconductor.

http://www.alldatasheet.com/datasheet-pdf/pdf/135752/AOSMD/AOU438L.html

VDS (V) = 30V
ID = 85A (VGS = 10V)
RDS(ON) < 4.5mΩ (VGS = 10V)
RDS(ON) < 6.5mΩ (VGS = 4.5V)

Datasheet mentions it is designed for low-side switching in CPU power conversion. So you could probably scavenge a suitable replacement from an old motherboard.

I imagine there are a bunch with the same pinning. They usually call this package a SOT-23-6 (for 6 leads..).

Generally you'd want 100V or so for PoE switch, for when the mosfet lets go of the coil, it will spring up some. If there is some snubbing maybe not too much, but I think 100V would be a safe bet.

What IC is used to control the FET? They usually are current mode and will sense the current in a small resistor from the switching FET's source to ground, <1 ohm usually. If we know the sense resistor and the SMPS IC, we can figure what the maximum current is also, to select a fet. :)

Edit: maybe I misinterpreted - is this switching the primary of the transformer? or just randomly somewhere in the circuit on the primary side? Might be for enabling PoE power to downstream parts, for example, after uh.. initiation. In that case, the protocol IC most likely limits current too - have to see it's datasheet to see if it switches the high side or the low side, etc.