diyAudio - pi filter in class a amp: okay to parallel inductors?

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jwb	19th October 2002 10:05 PM

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.

Jason Hubbard

20th October 2002 08:41 AM

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.

Elso Kwak

20th October 2002 11:33 AM

Low DCR coil

2 Attachment(s)

Hi JWB,
How about this one at
http://www.intertechnik.de/
?
2.7 mH; DC resistance 0.042 Ohm! part # 1340455:)

Elso Kwak

20th October 2002 11:43 AM

Another One

2 Attachment(s)

Hi JWB ,
Or this monster:
part# 1340690; 3mH 0.06 Ohm:)

cocolino

20th October 2002 01:52 PM

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.:confused:

Elso Kwak

20th October 2002 07:09 PM

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.:bigeyes:

cocolino

20th October 2002 07:56 PM

Quote:

sex/drugs & rock'roll I am too old for the latter two...

Elso:
I fear me too...:D but at least DIY audio falls in the drug categorie;) & rock'roll.... well, though I don`t practise it anymore I still like to hear it...

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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