I am using an isolated DC/DC converter to supply a MOSFET's gate drive, in a high frequency and high voltage application, so I am concerned about the EMI in my design.
In the website of the manufacturer, I could find this document that has a suggestion of external EMI filter (page 3 and shown below), but I am having some difficult to understand the suggested topology:
Usually, it is desired a low capacitance between primary and secondary of a isolated power supply. So the use of C2 sound a little bit strange for me in the first time, but I guess that it works like a shunt for the EMI, avoiding it to pass through the power supply. The use of the inductor L1 in series with C2 will create a high impedance for the conducted noise, making noise current flow very weak.
Even if my analysis makes sense, it does not seem to enough for EMI suppression. I usually see some sort of dissipative element to “burn” the EMI energy, like resistor or ferrite bead. So, in this circuit, the EMI will only be redirected to the input side, not dissipated. In addition, even if the EMI current has low amplitude (due to the filter attenuation) the non isolated side usually has sensitive devices, so it doesn’t sounds good to redirect the high frequency noise to this side. Would not it be better if it was shunt to another part of circuit and use a bead to dissipate it energy?
Can someone clarify what I am missing in the circuit's analysis?