Is this a right magnetics termination for PoE and non-PoE application

[FreshmanNewbie]

I've seen a couple of questions on Bob-smith termination for Ethernet magnetics.

But I fail to understand why the bob-smith termination is required?

Like, what's the purpose and how does the termination help to do what is required? Any value of RC is fine?

Since, I'm a freshman, can someone explain this is simple terms?

 

[D.A.(Tony)Stewart]

There can be large differences in grounds from each end from SMPS noise to line conducted leakage to ground to ESD noise to ground, To block most of this series CM 1:1 choke is used. The centre taps are ground connected but shunted to 0V ac to the local grounds to block differences between them somehow passed thru by imbalances in the centre tap and CMRR of the choke. Thus a LPF of 75 Ohms (?) 10nF (?) =C are used to provide local grounds for the signals used. Often n additional 1nF 3kV rated ESD capacitor is added in series so there are no DC connections between end signals or grounds.

Essentially it improves suppression of the line noise and the CMRR of the overall SNR of the Ethernet signals.

 

[FreshmanNewbie]

I came across the below schematic image while trying to read Bob-smith termination.

Would there be any problems with the termination on the right side with and without PoE?

Can someone explain a little on how the termination is different from Bob-smith and why?

 

[FvM]

Obviously no PoE scheme. A PoE termination needs to take car not to saturate common mode chokes by supply current.

The standard common mode ("Bob smith") termination uses one resistor per pair rather than a common resistor. Don't know where you got the particular schematic.

 

[FreshmanNewbie]

Obviously no PoE scheme. A PoE termination needs to take car not to saturate common mode chokes by supply current.

The standard common mode ("Bob smith") termination uses one resistor per pair rather than a common resistor. Don't know where you got the particular schematic.

Thank you. I'm just asking in General, in case the PoE is implemented in a design, is there a need to terminate the centre taps? If so, how?