I try to work in the handiest orders of magnitude, which for cores are cm or mm (mm wins because it's an even 10^3 out), uH or nH (I'll usually write mu_0 ~= 1.26 nH/mm, and A_L in nH/t^2 for lower values, but I went with uH for consistency here), MHz (problems are usually given in kHz, but you've got to admit, "0.2MHz" is a smidge faster on the calculator) and uWb (V and us). Adopting
I should add a note that some manufacturers work in kW/m^3 (Ferroxcube I believe usually does), which is equal as you say.
Further, I should change it for consistency's sake to uW/mm^3 (again noting the identity), or change the axis to read 10^3 smaller and go with mW/mm^3. Or W/mm^3 and label the axis with multipliers (0.1m, 1m, 10m, ...).
I did in fact change the horizontal axis on the plot; Micrometals gives their graphs in gauss and oersted, which just... oh come now. Yes, gauss are just teslas done with cm^-2 instead of m^-2, but that factor of it's-not-a-power-of-10^3 bothers me more.
Especially if they have trouble getting into that candy center, in which case a verbose title helps, or an index page.... but not some asshole Usenet poster shoving around links with no description. ;o)
And so on-- hence why I didn't cover that, because it's a whole mess of thermal budget and temperatures and airflow and blah blah blah... Highly important of course, just beyond scope. The procedure is given that, once you know how much power you can withstand in a component or its rough outline, you can find the power.
They do actually give some examples:
They also go into more detail on that "messy stuff" here (and in a few other articles), which is very useful. Some manufacturers don't bother (or their website is so old that it's impossible to find if they do), which is very nice of them.
Yes, and material, especially ferrite selection, is easily another short article's worth. Frequency, power, thermal, geometry, and maybe special purpose specs like tempco and linearity, etc.
Samey samey -- (most?) manufacturers go on Bpk for a sine wave, which of course is the only condition under which this is strictly valid (a square wave will have, say, 10 or 20% higher losses, which you can calculate knowing the harmonics).
Now, asymmetry and such, I've never seen data regarding that.
Let's see. Assuming losses are predominantly eddy currents (i.e., "classical Steinmetz model"), as it saturates, permeability drops, so skin depth goes up, which makes the particles look bigger, which should reduce eddy currents.
Depending on how you're driving (constant deltaB, H, ???), the amount of B-H curve traveled may or may not change. Eyeballing a B-H curve, the opening shuts off towards saturation, but that's not necessarily an indication that hysteresis is, in fact, smaller in that region, especially for a small cycle rather than full loop excitation.
Ferrites, at least, tend to get toastier towards saturation. I don't know if that's a nonlinear effect or just because, yeah, drive it harder and it gets hotter. Seems to me, manufacturers rarely provide losses in ferrite past 0.2T or so (i.e., not up to 0.3 or 0.4T depending on material and temperature).
Tell that to anyone who's tried using a #26 core in a boost converter. ;)
But as the point is being able to determine if it's right or wrong, anyone looking at a #26 core will be able to make that determination easily now.
In a properly made component, copper and core are equally important. As I observed, that #26 core might only handle a few VA, but the copper might handle 80W, nothing to sneeze at. It takes the right application.
Copper is probably more important than the core in RF chokes. For being a pile of dusty iron, mix #2 is surprisingly low loss: most points on the graph show a Q over 100. You'll be hard pressed to maintain a Q that high once you've put some pesky wire around it, especially the sheer amount you need to get a useful inductance from such a low permeability core. But then, I've got a power transfer mindset in that statement -- even at a few MHz, I need more inductance than an RF final at 20MHz does, which puts bigger demands on the copper, which either smothers the core or ruins the Q. Simple solution, buy a #8 or something higher permeability like that -- losses are higher, but you use less copper.
Micrometals strikes again on the matter: they published typical curves of Q vs. typical cores and materials for actual windings. Hard to beat that.
Yes, transformers have different limitations -- I went into some of this in an older article here,
Tim