Planar cores

Magnetics distributors like Allstar and Eastern Components (in USA) will do secondary operations and provide you with anything you want. One approach for planar cores is to have E-cores machined down....most of the legs removed...to required dimensions. Gapped cores can be cheaper than ungapped, because their faces don't need a fine finish. Asian ferrite suppliers will also accomodate, provided your volume is sufficient. Custom tooling for ferrites is quite inexpensive, since ferrites are compression molded. As far as models of cores are concerned, you can usually get away with using the same models for cut- down cores as you would for the complete core, since the gap(s) dominate their characteristics. Of course, you'll need to make some corrections for losses and their thermal consequences, since losses are proportional to volume. Paul Mathews

Hi Bob,

in the Philips Ferroxcube MA01 databook 2000, p. 39 Fig. 25, they have I^2L-vs-gap curves (IOW your Hanna curves. havent heard that name for a while now...)

I have it on PDF, its 6.3Mb, email me terry underscore given at ieee dot org and I will send it to you (or just that page if you like).

PhillipsFerroxcube (or whatever they are now called), along with Epcos (again, or whatever...) do a range of pre-gapped planar cores. they dont do gapped PLT cores though ;)

your qtys are high enough its worth buying pre-gapped cores. My personal preference (for E-E assemblies) is to use a pair of identically gapped cores, that way you cant screw up the assembly. It is, however, slightly cheaper to use one ungapped core and one gapped core, but of the four possible combinations, only one is right....

Cheers Terry