Author Topic: Ferrite beads vs Common mode choke for EMC?  (Read 1023 times)

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Offline FaringdonTopic starter

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Ferrite beads vs Common mode choke for EMC?
« on: July 09, 2021, 08:44:02 am »
Hi,
We all know how a single common mode choke is usually insufficient in an offline Flyback SMPS (10-70W). Common mode emissions can cause problems from 150kHz right up to 250MHz and beyond. No common mode choke can have good common mode attenuation over that bandwidth. As such, its normal to use a relatively large common mode choke of some 10mH or so, and to augment this with an upstream, smaller common mode choke, for the higher frequencies.

As such, I chose the B82721K2282U030 common mode choke as our “high frequency” common mode choke, and the wurth 744862100 for the “low frequency” common mode choke

However, looking at the attenuation graph, it looks as if we would be better off by simply placing a ferrite bead (Wurth 74275143) in the Live and Neutral lines. (instead of the B82721K2282U030 common mode choke) Would you agree?

B82721K2282U030 common mode choke
https://product.tdk.com/system/file...c/line-filter/data_sheet/30/ds/b82721k2xu.pdf

Wurth 74275143
https://www.we-online.com/catalog/datasheet/74275143.pdf
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