Re: CCFL transformer

On Thu, 25 Apr 2024 22:23:31 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

On 25-04-2024 17:08, John Larkin wrote:

On Thu, 25 Apr 2024 10:18:42 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:
 

On 24-04-2024 16:23, John Larkin wrote:

On Wed, 24 Apr 2024 09:37:24 -0400, legg <legg@nospam.magma.ca> 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

>
When there are a lot of turns, 3xFEP is not the way to
go. Too bulky. The three layers is basically a trick to
avoid creepage requirements for pri-sec safety. That's
not what you need here.
>
Anything off the shelf will be a great time saver.
>
RL

>
I sometimes use an autoflyback stage with a DRQ-series dual inductor,
followed by a c-w multiplier using sot-23 dual HV diodes. That's cheap
and easy, given a reasonable supply voltage, like 24.
>

>
I cannot use capacitive doubler thingies, there's no output DC voltage.
>

You can also just buy a potted HV supply and move on to design
something else.
>

>
I need it cheap, so cannot buy COTS
>

There are also potted c-w bricks, but they are a lot more expensive
than buying the diodes and caps.
>
Custom magnetics only makes sense at high volume, or for real exotica
like transmission-line transformers.

>
I have almost never used standard magnetics. Most projects has
requirements that dictate custom, or in higher volumes price is the key.
>

>
I'm about to embark on a custom tapped inductor and I'm not looking
forward to it. Drawings, quotes, revised drawings, more quotes,
samples, tests, released drawings, MOQs, all that.
>

>
Yeah, boring work.

 
What input do you have, and what output do you want?
 

>
I have 24VDC in, and 3.5kV peak pulse with 10% duty cycle at 100kHz. I
have a working circuit, but just a little too much loss due to the
transformer parasitics, so working to change the construction to get the
optimum transformer design

You could make 3.5KV DC, and then switch. There are high-voltage fets
around.

If you need fast rise/fall, or clean pulses, the transformer could be
difficult.