pi filter in class a amp: okay to parallel inductors? - diyAudio
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Old 19th October 2002, 10:05 PM   #1
jwb is offline jwb  United States
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Default pi filter in class a amp: okay to parallel inductors?

Is it kosher to parallel the inductors in a pi filter power supply? I can't really find the combination of inductance and DCR I need for a 16A +/-12V supply, so I am considering running the inductors in parallel. For example, 4x10mH inductors gives my an effective 2.5mH with a DCR of .064. Any problems with running these inductors in parallel?

As much as I'd love to use air core, the DCR is much worse so I have ruled them out.
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Old 20th October 2002, 08:41 AM   #2
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Default Parallel Inductors

I believe there is a small advantage in paralleling inductors in that the inductance will increase beyond the expected 2.5mh if the inductors are kept close and physically parallel to each other.

Other than that i'm not aware of problems relating to current sharing etc. though I must concede i'm no expert.
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Old 20th October 2002, 11:33 AM   #3
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Lightbulb Low DCR coil

Hi JWB,
How about this one at
http://www.intertechnik.de/
?
2.7 mH; DC resistance 0.042 Ohm! part # 1340455
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Old 20th October 2002, 11:43 AM   #4
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Talking Another One

Hi JWB ,
Or this monster:
part# 1340690; 3mH 0.06 Ohm
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Old 20th October 2002, 01:52 PM   #5
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Quote:
Hi JWB,
How about this one at
http://www.intertechnik.de/
Or this monster:
part# 1340690; 3mH 0.06 Ohm
Hello Elso:
Are You sure that those are suitable for DC-power supplies also?
I thought they are intended for AC-operation (speaker x-overs) exclusively and that they cannot take any DC-current (probably no air-gap) while maintaining inductivity.
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Old 20th October 2002, 07:09 PM   #6
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Default Airgap

Hi cocolino,
sex/drugs & rock'roll I am too old for the latter two...
Airgap can you enlighten me ? Has it to do with saturation of the core?? The transformer like inductors have a 7mm break in the core, the carbasse ones I have never seen in real life.
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Old 20th October 2002, 07:56 PM   #7
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Elso:
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Quote:
Has it to do with saturation of the core??
Yes, that`s what I have meant with airgap. If the core wouldn`t have a gap it would saturate with DC-currents quite easily . Inductors carrying DC current usually are designed so that the core structure provides an effective air gap to limit the DC bias current from excessively polarizing the magnetic material. As those coils for speaker x-over purposes usually wouldn`t have to deal with any DC there are likely not designed for this and therefore I`m not so sure if they can do a good job in DC-Power-Supplies as well.
I wonder from where do You have the 7mm break (is this gap?) number for the transformer like types??
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