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Old 4th February 2008, 07:18 AM   #1
jkeny is offline jkeny  Ireland
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Default Output Inductors

Can anybody say if the apparent closeness of these output inductors could cause problems - mutual inductance?
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Old 4th February 2008, 04:49 PM   #2
y8s is offline y8s  United States
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toroidal inductors tend to have a pretty tight leash on leakage flux. if you do the 'right hand rule' on them, you'll see that the field (at least in theory) cancels itself out.

so the effect is probably minor.
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Old 5th February 2008, 07:55 AM   #3
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Even if the flux was 100% contained within the toroid, there would still be a 'virtual' single turn air-cored coil when you wind a toroid as a single winding. You can wind half the toroid and then take the wire diametrically across to the other side and finish winding the other half. (As seen in the better type of inductors on some SMPSUs). This cancels out most of the 'virtual single turn' effect.
(Bruno Putzeys for example stresses this point quite often. I know he frowns upon toroids that are not co-planar to the pcb).

So basically, in your photo, from the mutual coupling point of view, you have a number of single-turn air-cored inductors in line. There will be some coupling but I doubt if it will cause any problem.
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Old 5th February 2008, 08:30 AM   #4
Eva is offline Eva  Spain
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Winding toroids in two opposed "runs" as encouraged by some authors does *not* solve the parasitistic turn problem at all. It just produces an eight-shaped dipole. Near field improvement on leakage flux is marginal, except exactly on the perpendicular axis where flux cancellation arises. Furthermore, far field leakage flux in toroids is negligible so no improvement is easily measurable either.

Don't worry that much about these toroids.
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Old 8th February 2008, 12:31 PM   #5
ranga is offline ranga  Romania
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Quote:
Originally posted by Ouroboros
Even if the flux was 100% contained within the toroid, there would still be a 'virtual' single turn air-cored coil when you wind a toroid as a single winding.
Would this configuration solve the issue?
Click the image to open in full size.
if you compute the inductance as 2 series inductors and wind them at 180 degrees they will cancel each other (the fields from each single turn air inductor). Am i right ?

edit: Sorry about my MsPaint skills !!
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