Paralleling L-C feed-thru filters for increased current capacity

Aug 04, 2007 1 Replies
M

I'm currently working on a power supply which must meet the EMC requirements of def-stan 59-41 land class A. The power supply is housed in and aluminium enclosure with separate chambers for the various sections of the power supply. The initial design which I wasn't involved in uses multiple feed-thru filters connected in parallel when passing connections through the internal bulkheads, the currents involved are around 30A. My gut feeling is that this is a bad idea, partly because they my not share the DC currents evenly, but more of a concern is that connecting them in parallel will create high Q L-C resonant loops detrimentally effecting the EMI filtering.



Has anybody ever successfully paralleled feed-thru filters or should I just try to source larger feed-thru's capable of carrying the full currents involved?



Mark



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T

If they're all the same model and make they should have similar DC resistances -- you could check. The inductors will be made with metal wire, whose resistance increases with temperature; if one starts to get hot it'll tend to shed load onto the others.

Many near-identical L-C filters in parallel will make a filter that's a bit broader, but no more highly resonant than one. I think you're safe there.

If it's _really_ a concern, why not test for it?

Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
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