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Old 20th November 2003, 05:41 PM   #1
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Default Common mode filter choke...

Hi,

While I was cleaning my room I found this coil looking thing and so I surf the net and found out it was called a common mode choke. I have a bunch of this lying around, what are they for? Can I use them for filtering my supply rails? Are they for AC or DC? What should I do with them?

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Old 20th November 2003, 09:17 PM   #2
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JoJoD,

those are very good for blocking common noise (i.e. noise which is present on both wires).
You can use them in your mains AC line input, or if they are beefy enough at the secondary of your transformer before the rectifier.
Make shure the coil doesn't get saturated by to much current going through, as it won't work anymore. Because of this it is not recommanded to use it with DC current.

Dick.
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Old 21st November 2003, 01:54 AM   #3
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djmiddelkoop,

Thanks for the idea. So I can use it for AC mains conditioninig. They look like this...
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Old 21st November 2003, 04:58 PM   #4
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Yes,

they are perfect for that and that's the way they look like.

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Old 22nd November 2003, 12:13 AM   #5
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Hi,

I also have a bunch of those small toroidal looking chokes that came from pc psu. I was hoping I can re-wound it and make use of it in filtering mains or my rails just before the bridge rectifier.

JojoD
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Old 22nd November 2003, 12:23 AM   #6
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they can make nice effieient switching inductors for a small SMPSU....been doing that for a long time...
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Old 22nd November 2003, 06:29 PM   #7
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JoJod,

no don't rewind these chokes but use them in your AC line filter as well !
For instance, put then in series with each half of the commonmode choke or after your rectifier diodes for noise surpressing.
As you may understand these chokes work only with high frequencies usually those out of the audio bandwith.

Dick.
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Old 22nd November 2003, 09:58 PM   #8
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Quote:
no don't rewind these chokes but use them in your AC line filter as well !
Alright! I knew it all along, these things still has some use.

Thank you...

JojoD
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Old 23rd November 2003, 12:30 PM   #9
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they've got a lot of uses...filtering line noise...such things...might find a few outta monitors and such
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Old 23rd November 2003, 01:56 PM   #10
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I just asked a friend who has a pc repair shop to give me his junk pc psu... the chassis is good for test psu, the caps inside are also good for filtering and then, there are lots of those toroid looking filters!

If you guys have some sample implementation for such.

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