Hello,
I have a PoE camera and want to run some 5V accessories near the camera with using only one network cable to the location.
So I was wondering if I could "piggy back" off of the camera's PoE power. I can't really open up the camera - so I would have to hook into the ethernet connection and get the power from there.
The idea is to have the camera connect normally to PoE power and after full power is supplied, have a BUCK converter that draws from the 48V on the ethernet cable and steps it down to 5v.
The issue is that the PoE handshake is failing and I'm not sure what the reason could be.
My circuit is attached below (i.imgur.com/mZqmI1n.png), here is the idea:
- When the PoE camera is connected to the PoE switch the the switch will initiate the PoE handshake by sending voltages <25v.
- At this point, since the voltage is <25v, my circuit should have no effect due to the D3 28v Zener Diode which will not conduct - having Q1 isolate the BUCK converter from the input.
- After the handshake completes and the voltage goes up to 48v, D3 ill conduct, enabling Q1(2n7002) and providing power to the Buck converter.
However, when I connect the circuit, the hndshake never completes and the switch never ends up delivering any power.
If I isolate Q1's drain (Q1 drain will be left floating), then the PoE handshake is complete and everything is working.
Also, if I tap the PoE connection with my circuit , but after the PoE handshake has completed, then everything works.
Any idea what the issue could be here ?
- I tested if my circuit draws any power @25v - but the amperage drawn was < 0.1mA
- I tested the capacity of my circuit and it was 33pF - which shouldn't affect too much.
- I've tried hooking up a scope to observe how the signature is failing but I didn't see anything special there.
Compoenets:
BR1, BR2 = UM1B Diode Bridges 25A 1.1V@800mA [
Datasheet]
Q1: 2N7002 N-MosFET [
Datasheet]
D3: MM1Z27W 27V Zener [
Datasheet]
D4: BZT52C15 15V Zener [
Datasheet]
Any Suggestions appreciated, thanks!