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Old 5th December 2009, 05:09 PM   #1
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Default pi filter variations

'Hope the following image is legible...

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A is the typical choke pi filter. B has the choke on the ground side. C has both. I can't model either B or C in PSUD (as far as I can tell anyway). So a few questions:

1. Is there any disadvantage to B? It seems like a good option for situation when choke doesn't have a high enough voltage rating.

2. Does C have any advantage over A or B? Or would two such chokes, say of equal inductance, be equivalent to having one choke (as in either A or B) of twice the inductance?

Thanks for any help.
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Old 5th December 2009, 08:36 PM   #2
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There is not really any disadvantage to B, in fact it is chosen for the very reason you cite. Of course, circuit common must come off the negative end of the second filter cap.

C might be a tad bit advantageous in reducing common mode noise, but power chokes are somewhat limited in their ability to block RF. C is what I use in my preamp.

For the purposes of PSUD, there is no difference between A and B, and to model C you add the inductances of each individual choke, modeling it exactly the same as A and B.
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Old 5th December 2009, 08:44 PM   #3
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274A Datasheet. Emission Labs.
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Old 6th December 2009, 01:42 AM   #4
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One Electron also makes dual wound chokes and I have a few of them. I never thought to use them like the above Emission Labs diagram. Interesting.
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Old 6th December 2009, 05:42 AM   #5
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Quote:
2. Does C have any advantage over A or B? Or would two such chokes ...
As drawn and explained in the original post, separate (two) chokes for "C" would be the same as doubling A or B. There would be no advantage to C.

However, if C used a single core with dual windings, it would act as a common-mode choke as illustrated by nicoch46.
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Old 6th December 2009, 01:52 PM   #6
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Default So this bridge arrangement ok?

I am liking the dual wound choke idea. Would the following full-wave bridge arrangement be correct with a single core/dual wound choke like the Lundahl or One Electron mentioned?

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Old 6th December 2009, 03:02 PM   #7
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more info
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Old 6th December 2009, 04:24 PM   #8
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Yes, that is the correct use of the common-mode choke.
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