Common mode choke with true bifilar winding?


Designing the umpteenth higher power RF filter here and wondering. Are there any truly bifilar-wound common mode chokes? Maybe some niche shop in the boonies makes them? I've been through the usual places such as Pulse and Gowanda.

I'd need 100uH or more, 1A of (differential) current with 2-3A preferred, thru-hole would be nice but not required, and leakage inductance is very critical because of a somewhat sensitive filter requirement. 300nH or maybe 400nh could be digested but not more.

So far I've always done that with some big double-hole ferrite cores and coax but this gets old. Mostly because that's bulky, you need 3-4 in a row because you can't get more that two turns of RG174 through those and the manufacturers never offer any kind of fastening material. Seems the issue of having to mount them onto a board or chassis is beneath them. Plus it's a custom part we have to hand-wind in production and off-the-shelf would be more desirable.

Commercial ones either have double-chambered bobbins which results in horrible leakage inductance or they look like this and still have almost

2% of nominal as leakage:

formatting link

Insulation strength between the two wires won't matter, there's never going to be more than 100V and there is going to be a safety shut-off in case it goes kaputt.

Regards, Joerg
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