Re: CCFL transformer

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.
>
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.
>

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.
>
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.