Common Mode Chokes for dummies

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My electronics is a bit weak and I am trying to figure out how to pick a common mode choke as per recommendation of a PSU module.

 

now, for pricing purposes, I have to use this AC/DC module, looking at the typical application circuit, the EMC recommended circuit recommends:

  • for the input - green ring 15mH 2.5A T12 x 7 x 6 CMC
  • for the output - green ring T13 x 8 145uH CMC

the module operates on a 65kHz switching frequency.

 

I am struggling to pin point what kind of choke I should be looking at? is the max current enough information to pick the cheapest choke in Digikey?

what should I be looking at in terms of picking a common mode choke for both input and output of this circuit?

Ovi2wise
Digital electronics student... forever a student

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Current rating is generally "the big one", but it is not as bad as the energy storage inductor in a switcher, because there are opposite-flowing currents that reduce the DC flux in the core.

 

Common-mode chokes tend to be good over a fairly wide range of frequencies. So, the precise operating frequency of the switcher should not be critical. Honestly, I don't know what "green ring" refers to; I have never seen that designation. It may signify a specific magnetic material, but I don't know how to interpret it. Those are likely "ferrite" cores. I am guessing that L2 is 12mm outer diameter. Probably 6mm thick and 7mm difference between outer radius and the inner radius (e.g. radial thickness). Or, visa versa. 

 

Not sure that I would use "cheapest" as a selection criterion. I would simply choose one that works.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

Last Edited: Sun. Oct 18, 2020 - 05:55 AM
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Very often, you just want this  (line filter) ...there are 1000's of models, some include a fuse holder...I have a giant scrap box of about 50 types---a few are high current versions

 

look here ...GREAT prices & wide variety

https://www.alltronics.com/cgi-b...

 

higher price

https://www.digikey.com/en/produ...

 

you can get some good deals on scrap ones  The big one has a fuseholder & switch & mavbe 110/220 voltage selector (not sure)

 

Honestly, I don't know what "green ring" refers to    --I'd never heard of it either ....kinda funny stuff, these Chinese desc

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sun. Oct 18, 2020 - 06:28 AM
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IIRC, a few years ago I helped one of my sons build a coil for physics class.

It turned into such an ordeal that I posted about it here, but I've not found the Thread with a quick search.

In any  event, IIRC, the color had to due with the magnetic permeability of the toroids, and hence their inductance.

 

JC

 

Edit:Typo

 

Last Edited: Sun. Oct 18, 2020 - 05:37 PM
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https://electronics.stackexchang...

 

In summary... no, each manufacturer has their own colour code.

Ross McKenzie ValuSoft Melbourne Australia

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I wonder if "green" means environmentally friendly.

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I wonder if "green" means environmentally friendly.

Why do you thunk they call it earth gnd?   Have you ever traveled on a ground plane? 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!