The Wire Crossing a Toroid Winding Technique for Lowering Parallel Capacitance

D from BC · 2007-10-18T08:59:01+00:00

I'm aware of winding spacing and gap between first and last loops toreduce toroid interwinding capacitance.Then there's the winding technique where 1/2 the toroid is wound, thenthe wire is pulled across the toroid to the beginning...and then thewindings resume. (one layer)Normally with a continuous winding, the first and last loops meet andthis can be a heavy capacitance point due the Vdiff.With the 'wire over the toroid' winding technique, 2 points ofgreatest Vdiff are created. Each point with 1/2 the Vdiff compared tothe continuous winding. I recall a while ago somebody posted that the 'wire over the toroid'technique can significantly lower inductor parallel capacitance.I'm scratching my head on:1) Does that 'wire over the toroid' have a name?2) How does the 'wire over the toroid' technique reduce capacitance??Is it the 2 points with 1/2 the Vdiff compared to normal winding?Is it that the electric field gradient shape has changed from 'O' tomore like an '8'??D from BC

P

Paul Mathews 18 years ago

The notions of lumped capacitance, resistance, and inductance, are all useful. However, if you're working in switchmode, what you'd often like to do is to maximize SRF. The higher the SRF, the less power loss in snubbing, for example. Sometimes, we focus on some particular parameter like leakage inductance, but it is really about minimizing energy storage in parasitics, including capacitance. Having said that, it's worth mentioning that you might find yourself actually going the other way entirely with quasi-resonant designs. Paul Mathews

Vote

D

D from BC 18 years ago

Digital is sooo much easier.. With smps development, seems like everything jiggles like jello. :)

After some googling, I've noticed that commercial toroid inductor makers seldom have the srf on datasheets.??? Now that tells me something.. Under the 'if you can't find it you don't need it' philosophy, it means self resonant f is not important enough to put down on a datasheet... This makes me assume the off the shelf toroids have srfs high enough to be manageable. (I'm also a newbie with snubber circuits but have a fair understanding.) Or...it just means... if I want a particular inductance .it's going to have it's associated Cp and srf and that's the way it is.. Tough! It's up to other circuits to deal with it or control it.

Yeah... I've been thinking about resonant designs.. Quasi-resonant is like a 'why fight it...join it' approach. I'll check it out.

D from BC

Vote

C

colin 18 years ago

with high voltage resonance is unavoidable, as the number of turns for the secondary/whatever gets higher, the capacitance goes up fantasticaly, srf falls even quicker.

resonance has been used in tv eht circuits for decades.

im sure farnell and digikey list srf for inductors, but cant say i recal for sure if they do for torroids.

for low voltage dc to dc converters I dont think its ever a problem, except maybe EMI.

Colin =^.^=

Vote

P

Paul Mathews 18 years ago

Real magnetics components depart widely from the ideal, and many are poorly specified. Many circuit designers don't really know how to apply them properly. Do some reverse engineering, and you'll find lots of unnecessary shielding components, extra EMI filter stages, and unnecessarily slow control loops out there in the real world, often because designers don't really know what they're doing...they keep adding components instead of solving basic problems such as high energy parasitic oscillations. One more common example: quite often magnetics are unpolarized, in the sense that you can plug them into a circuit board in 1 of 2 orientations 180 degrees rotated. This can make a tremendous difference in conducted EMI, since it can put the outer turns of the component closer or farther away from a victim circuit element. Details matter. Lots of people in the magnetics business don't really know their trade beyond getting UL recognition and making a component with nominal spec sheet characteristics. Don't be surprised if their datasheets seem to lack some really important information. Paul Mathews

Vote

D

D from BC 18 years ago

On Sat, 20 Oct 2007 17:13:03 -0700, Paul Mathews wrote: [snipped quoted text for less scrolling]

Just shocking! I just assumed ..."They make toroids...they must be magnetics experts"

I was on the JWMiller site (now Bourns) and the Pulse site (the planar magnetics look cool)..and I didn't see any f sweeps or srf specs for toroids for smps use in the 100W to 200W range. I was on these sites just to see if any special winding patterns where used on toroids. The horizontal mounted toroid on the JWMiller site looks like it has the 'wire crossing the toroid' winding (or call it cross wired split winding).....but no srf specs to compare with regular winding.

formatting link

Besides....I suspect it's just a plain regular continuous chain of windings.... The wire crossing the toroid is just for lead position. It's a fake. :)

So I kept searching and got Google tired and have yet to find any images of a low Cp or high srf toroids for smps use that use an alternative winding technique..

D from BC

Vote

D

D from BC 18 years ago

Yes! :) So that's the name of that type of winding on a toroid.. It's what I've been lengthily calling 'the wire crossing the toroid winding technique'..or 'wire over/across the toroid' or another described it as a split winding cross wire winding.

Anyways ..Googling away :)

Thanks

D from BC

Vote

G

Graeme Zimmer 18 years ago

Hi,

I'm a bit late with this, but the technique is called "Regressive Winding"

see bottom of page

formatting link

Google has a few references as well...

regards ................. Zim

Posted via a free Usenet account from http://www.teranews.com

Vote

D

D from BC 18 years ago

Thanks... Somebody else did post the name of winding prior.

I did some Googling on inductor sites and I've yet to see a toroid in production using the regression winding technique. Either it's a specialty item or expensive to produce or doesn't help or has limited application or I just haven't searched enough, I dunno yet...

I do plan on some experiments.

D from BC

Vote