I've designed this simple circuit that uses a Silvertel AG9205 PoE PD module in order to extract 5.65V from the RPI PoE header pins.
Here it's the schematic:
In order to be careful, I've placed a SS34 Diode as reverse voltage protection directly at the +VDC output pin of the module.
Now, here comes the strange thing. When powered up, the board itself produces a strange noise (like a whistle) that comes from the capacitors, after three or four seconds, the Poe PD module goes in toshutdown mode.
When I remove the diode and bypass it with a jumper wire, the problem disappears.
Initially, my doubt was regarding a faulty diode, but measuring with a multimeter the diode it shows a voltage drop of 180mV, so it seems okay. In addition, I've tried another board and it shows the same symptoms
Where is the problem? I really can't understand it.