permanent magnets as coil cores

Pre-biasing the operating point on the B-H curve ??

...Jim Thompson

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"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

... so the remanence field strength is of opposite polarity and approximately equal magnitude to the field from the DC and low-frequency content of the current in the winding, increasing the margin against loss of incremental permeability and saturation of the core?

Chris

Causing the two coils to align themselves would seem to be an obvious benefit.

Yup. Old trick. I recall seeing some surface-mount inductors that do that, too.

John

Ok, that's right. I didn't think of that. Just never seen it before.

Hmmm, interesting.

Those things are in, yeah every single monitor I've taken apart. Always something there that clings to your pliers when you desolder it. :-)

In particular, I think they're usually wound from Litz wire, and found in the horizontal deflection circuits. I seem to recall one was used in an Apple monitor as a flyback supply for something, switched by an IRF640. I don't remember if that was supplying power to the FBT, that's usually supplied by the power supply itself...

Tim

-- Deep Fryer: A very philosophical monk. Website @

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You may be mistaken. It is more likely that a small section of a core is pre-biased, as the materials used for PM tend to be poor candidates for efficient HF AC flux imposition.

Some polymer composite material and is used in LF motorc - which is where magnetized material finds more frequent use.

Hitachi used to sell pre-biased E-core magnetics under the 'Hicoil', 'Hicoil-L' and 'Hiformer' trade marks, for applications below 100W and

40KHz. An EDN article from July 19, '78. It's not the kind of product feature that would be easily recognized.

If your device is a non-contact inductively coupled charger, which the term 'inductive charger' suggests, the presence of permanent magnets may have nothing to do with efficient power conversion, and more to do with maintaining coupler surface contact and orientation in the charging station.

RL

Guitar pickups are like that, because the string isn't magnetized, so the coil just senses the changes in the flux when the string vibrates. But I don't know how it would contribute to a "charger"; albeit you haven't really defined the term "charger" in this context.

Good Luck! Rich