Edit, changed circuit diagram to make explicit the signal source is the load
I'm designing a medical device and I'm in process of determining the line filter I'm going to need. I'm not especially concerned about incoming noise but rather the outgoing conducted noise. The device in question is somewhat chunky (1kW) so the conducted emissions are non-trivial.
Now on medical devices you're not allowed to have the common garden Y-filter, medical device line filter looks like this:
I've created differential and common noise models for the input filter using Würth electronics WE-CMB series 1mH 10A CMC, I'm using 220nF for the X2 cap here but that's subject to change. 53R in the differential model is the 1kW load I've got. 1meg resistor in the output is to discharge the plug when disconnected to comply with regulations.
The common mode variant tracks pretty well what Würth says it should do so I presume that's fine.
My problem is that the differential filtration is too good, I'm suspicious of it, around -40dB at 1MHz. Can anyone point out something obvious I'm doing wrong with the differential model?
The 50R star mains line model I've seen in couple of different variations, one example uses 68R but the test equipment is 50R, so..
There's some really unfortunate peaking going on around 135kHz but there's not much point addressing it if my model is out of whack.