I'm working ona a design around a zp42915-tc ferite torroid and a switching supply.
One of the secondaries only requires a single turn. With bobbin would transformer I'd spec out a turn of foil wide enough to utilize the entire width of the bobbin. never did this for a torroid. How do I wind this to minimize leakage inductance?
switch freq is 150K, full bridge topology.
You could use a foil as well, but not a straight piece. It needs to be cut a bit skinnier inside the toroid so it won't wrinkle up too much. Terry Given does a lot of this stuff, maybe he could share a photo.
I usually use litz wire and then come off the toroid core in twisted pair fashion. If you can consider a pot core instead that would be easier. Of course those aren't as mechanically robust as a toroid.
The Motorola HF power amplifier app notes in the '80s had you use toroids stacked on a piece of brass tube (or two, side by side), with the rest of the windings through the middle of the tube.
Dunno how it'd work on a switcher, but it seemed to work well in a class AB power amp at 20MHz.
That's how we did it in ham radio. I was young and the issue wasn't so much the performance but how many of those toroids where in the budget.
Do those old app notes still exist somewhere on the web?
For us it had to work up to 30MHz and it did. Except for that one balun that exploded and sent ferrite pieces plus the dipole wires flying ...
-- snip --
Try the Communications Concepts web site -- they used to sell kits based on those app notes, and (AFAIK) still do.
I think that if you experiment with an ideal ( even if impactical) form, you may be disapointed with the results, using a single toroid.
I know I was (but then I was working with minimal permeability material).
At least you'll have some standard of quality when you measure practical alternatives.
RL
Yes, thanks! In case anyone else is interested here they are:
On a sunny day (Sat, 17 May 2008 11:25:35 -0700) it happened Joerg wrote in :
Thank you, just been reading through those. Nice stuff.
Hi Joerg,
I cant see ABSE, but feel free to post the pic of my 2500W transformer....
Cheers Terry
You could use three or more foil windings and just connect 'em in parallel.
I do like the brass-tube-through-the bore idea, it would save the fingers from shoving little copper strips in tight places...
Ok, done, it's on a.b.s.e. now.
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