Re: Drum Core Stray Magnetic Field

The first tests:

Side to side and top to top are good, bottom to bottom (mounted on each side of 1.6mm PCB) is not as good, but not way off

Cheers

Klaus

Bad news! I can't get ANY model to fit the data sheet! within the constraints of physically realizable components.!! I drew the expected structure, filled the window with 38 AWG wire, wire is getting small already, got the 330uH, but got 3.8 ohm resistance! too high and there's no room for 'fatter' wire! Consdiering this component is 'early' in their product offering you got me what's going on! For higher values of inductors they have to use smaller wire. I know credit card size modems contain telco transformer that use 54 Awg wire. maybe they just go right on up.

If you get one of these parts, measure the 'lid' thickness, the heighth of the coil window, and the heighth of the bottom 'lid'. They should add to 3 mm. If you have a microscope, see if you can discern the wire gauge.

You got me, I don't know. Maybe the 'cut' into this bobbin is huge. But even with that, trade-offs stop achieving much.

FWIW, years ago during tenure in the Aerospace Industry, we tested the reliability of little transformers that used little wire. Simple temp cycling test. Ten cycles, full range temperature cycle over twice a day, test took five days. If the wire was too small the rransformers failed. Conclusion: Don't use ANY transformer with wire size smaller than 44 Awg. The expansion/contraction of the temp cycling and the physical structures having different rates of expansion, literally broke the wires.

bad link. did you put the whole line inside ?

Try cut-n-paste of the entire line into your browser. Worked that way for me.

Old excel format:

Cheers

Klaus

Maybe it's a high perm core?

I will measure what you asked for and post back

Cheers

Klaus

Klaus,

Please do it next time with angle brackets:

Or write it up in plain English. I hate spreadsheets.

Got it !! Thanks

I saw that 'brackets' made NO difference to someone's requesting you use brackets. But this should work for others:

When you get your sample, please count the turns on that top layer.

Forgot to ask for turns count on top layer. I didn't try infinite perm, perhaps I should. But I started with perm of 200 and got around 320uH then went to perm of 2000 and then the inductance only went up to 350uH. Remember from air core to perm core is only 5.4 on the SDR0403-4R7 An open core 'rod's effective permeability is based upon the length dieamter ratio NOT the perm.

Last page of Fairite catalog, circa 70's shows an excellent plot of effective perrm vs length to diameter ratios AND permeability. The curves asymptotically limit to a function of length to diameter, independent of high perm.

Anybody have a copy of that page? I can't find mine! not long ago I think someone posted it here, I got a copy, and can't find where I put it!! Just because I did not name it correctly. Or, put it in the right folder.

I searched a while and found it in the 13th edition, page 24:

Thanks for posting! ...but that's not the page, although has the information.

The back page of a 70's print catalog? You might try Snelling's 'Soft Ferrites' for a reliable reference. I believe he worked for Mullard/Philips.

RL