Inductors in parallel - Brilliant or wacky?

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ian
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Inductors in parallel - Brilliant or wacky?

Post by ian »

Hey guys. I'm making a pc board for a switching power supply rated at 2 - 3 Amps. The switcher requires an inductor of 100 - 200uH. I might make a lot of these as I am trying to design a cool product for hackers like us. Here's the thing.........
I bought a big bunch of surplus inductors rated 330uH @ 1.6A. Now, if I parallel them theory tells me I'll have a 165uH inductor @3.2A. The problem with theory is.............................
The other thing I'm wondering about is if I mount them on the pc board side by side will the magnetic flux be in opposition between them. Or is the field so small I shouldn't worry about it? Or should I reverse the polarity of one so that the magnetic flux between them is in the same direction?

Is this whole thing wacky? brilliant? or is it just a normal thing that should work?
Dean Huster
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Re: Inductors in parallel - Brilliant or wacky?

Post by Dean Huster »

Inductors with cores won't effect each other that much. their values are usually so large that the small amount of coupling they might have would be minimal. Air core inductors that are even remotely near each other can be disastrous. I hate English sometimes. It's a disaster but it isn't disasterous. What gives there anyhow?
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.
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jwax
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Re: Inductors in parallel - Brilliant or wacky?

Post by jwax »

Right on Dean. If they're toroids, even less concern about coupling.
How about strapping a pair of them down, and measuring Ltotal?
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ian
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Re: Inductors in parallel - Brilliant or wacky?

Post by ian »

I guess the effect could be measurable in controlled conditions. If it were a fixed frequency switcher what would change if the inductance was larger or smaller? (Given the same load and input/output voltage).

I do not believe it is an air core inductor as the spec sheet says "High saturation core material used for
high inductance and low DCR." The inductor is an apc30-331k from alliedcomponents.com.

Unless I could measure the magnetic field with a 100MGHZ magnetic flux-o-scope.
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haklesup
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Re: Inductors in parallel - Brilliant or wacky?

Post by haklesup »

Give it a try, it might work. Is this component used in the energy storage part of the circuit or in the output smoothing filter? It might not work as well as the main energy storing inductor as the energy will be divvied up amongst each inductor. It works on paper but might be sketchy in application with possibility of individual inductor failure if current hogging occurs doe to some obscure layout condition. The configuration you lay them out may be important. Rather than paralleling them up axially, consider creating one central node and a ring node around them forming a kind of doughnut
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