Re: CCFL transformer

On 27/04/2024 12:24 am, legg wrote:

On Fri, 26 Apr 2024 01:36:06 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
 

On 26/04/2024 12:52 am, legg wrote:

On Wed, 24 Apr 2024 01:57:36 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:
>

Hi
>
I need a low distributed capacitance winding transformer, for a HV
stepup function (3.5kV)
>
I am zeroing in on similar concept as CCFL transformers with
sectionalized bobbin.
>
For example:
>
https://www.coilcraft.com/en-us/products/transformers/power-transformers/ccfl-transformers/fl/
>
Possibly using Triple Insulated Wire to create some distance between the
individual turns.
>
Not many sells CCFLs these days.
>
Guess I will keep it alive....
>
Regards
>
Klaus

>
Stress between turns is limited by v/n limit of core. It's layer
stress and section stress that you have to deal with.
That's what the multisection bobbin and pancake windings do.

>
They also reduce the parallel capacitance of the windings, and give you
are higher resonant frequency for the transformer as a whole.
>
"Layer stress" and "section stress" aren't specific electronic
engineering terms, and the "v/n" limit of the core is pretty vague.

 >

If you wind transformers, they are all pretty straight forward terms.

I have wound ferrite-cored transformers from time to time, and they stuck me as unspecific word salad.

There is a volt per turn limit imposed by the magnetic field that
saturates the core - but at higher frequencies you can tolerate more
volts per turn before the core saturates - it's a linear function of
switching frequency, up to the point where resistance around the current
loops inside the core lets enough current circulate to heat the core
above its Curie temperature.

 >

The physical limit of saturation at lower frequencies and core loss
at higher frequencies is a basic trade off in ferrite design.

Obviously.

If the CCFL transformer will allow only 1600V, imagine the
precautions required for 3x that stress. I'm not sure you
can avoid vacuum impregnation / potting in anything 'small'.

>
Imagination does seem to be what's being applied here.

 High voltage design is worth serious study, before spending the
shekels. I'd suggest consulting someone with previous experience.
Imagination vs 'Why you can't do that' is a tiring back and forth.

>
There's a least one truly horrible 1969 text book on transformer design
>
https://www.amazon.com.au/Soft-Ferrites-Applications-C-Snelling/dp/0408027606
>
and it took me years to realise quite how confusing it was.

 In my day, it was considered to be the bible, but I could never
afford a copy, so depended on photocopies and library access.

I worked for EMI Central Research at time I thought that I needed it, so access wasn't a problem. The Seimens soft ferrite application notes turned out to be a great deal more useful, and much better organised.
The late great Tony Williams passed out .pdf copies to his s.e.d. mates
They started off with the transformer equation, and I don't think that that ever showed up in Snelling's book.

One of the earliest comprehensive studies of ferrite material apps.

Comprehensive perhaps, but vilely organised and incoherent.

There's an electronic version of the first edition on line, for
those interested.

And silly enough to risk it.

It has a later revision (~Y2K), that I also can't afford.

Don't bother.
--
Bill Sloman, Sydney