Common Mode Choke question

Hi everybody,

I have a 1mH, 10A common mode choke. Can I use this as an inductor with the same specs? If yes, how? Like (a) connecting one winding and leaving the other open or (b) paralleling both.

Thanks, Mohit.

Reply to
schouse
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** No. It is a essentially low current inductor of 1 mH.

A genuine 1mH, 10 amp inductor will have a laminated iron core and be about the size of your fist.

...... Phil

Reply to
Phil Allison

Thanks for the reply. But I don't understand. How is it a low current inductor? The choke uses a toroid and is about 25mm(dia)x20mm.

Please be k>

Reply to
schouse

Thanks for the reply. But I don't understand. How is it a low current

** Go look up "core saturation" on Google.

A " common mode " choke avoids the problem by having equal and opposite currents in two coils.

A genuine, high current choke must be of reasonable core size and have an air gap in the magnetic circuit.

........ Phil

Reply to
Phil Allison

Sorry, no. A common mode choke is wound such that the load current (the one rated at 10 amperes) trough one coil magnetizes the core in one direction, while that same load current, returning back out the other winding, magnetizes the core in the other direction. So the fields of these two currents cancel, preventing the core from saturating, and producing very little inductance.

The device shows 1 mH only for current that goes through one or both windings in the same direction, so that the fields do not cancel. In line filter applications (where these devices are usually used) this common mode (same direction in both sides)current is very much smaller than the load current (that goes in one winding and out the other).

For instance, the common mode current may be a result of voltage that is in common on both line wires, like signals picked up from local AM stations by the line wiring acting as an antenna, or generated by diode switching or switching regulator operation on the load side.

The core of a common mode inductor is generally a solid, high permeability ferrite (with no air gap) to maximize the winding coupling and inductance, since the common mode signals are generally very much smaller than the load current. They are really a form of transformer with two equal windings.

Normal mode inductors (two lead devices) generally are made with distributed gap powdered iron material that takes a lot more turns to produce the same inductance, but are saturation resistant, because of the nonmagnetic gaps in the flux path that store energy when a magnetic field is forced through them.

Reply to
John Popelish

If you can get at all the leads there should be no reason why a suitable cross connection couldn't effectively parallel the windings.

  • * 1----+ +----2 ) ( ( ) ) ( ( ) ) ( 3----+ +----4

In common-mode configuration the input connections are to terminals 1 and 2, with the load connections being 3 and 4. Current entering at 1 will return via terminal 2, so the fields oppose and cancel.

Connect 1 & 2 together and 3 & 4 together to form a two terminal device and you should end up with the fields reinforcing rather than canceling.

Reply to
Greg Neill

Yes, the zero current inductance will be about 1 mH, and the windings will handle about 20 amperes. Unfortunately, the core will saturate with something like a fraction of an ampere.

You could also connect 2 to 3, and between 1 and 4 you would have about 4 mH zero current inductance, and the windings would carry about 10 amperes. but the saturation current would be about half of the first case.

Reply to
John Popelish

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