One possible way would be to add common mode choke. It can be done by making few turns (as many as possible) of the power cord on the large ferrite (chose one with the highest permeability). When wires in the cable carry current in opposite direction (normal/differential mode) magnetic flux is induced in the ferrite in opposite directions resulting in cancellation lowering inductance almost to zero. Common mode interference induces currents won't cancel, being in the same direction, producing inductance in series with both wires. This scheme works well at high frequencies only since it is difficult to put many turns of power cable on the ferrite. It is possible to build common mode choke for lower frequencies. It is pretty much 1:1 metal core transformer with identical windings connected as a common mode choke (in series) and not as transformer (in parallel). As long as windings are identical inductance for differential signal will be zero. I suspect that many power conditioners might have common mode choke in addition to normal mode filter.
9 responses Add your response