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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: CCFL transformer
Date: Fri, 26 Apr 2024 00:49:52 +0200
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On 25-04-2024 23:29, John Larkin wrote:
> 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.
> 
I have looked into that. I cannot find resonable valued transistors at 
4kV, prices ranges above 20 USD per piece. But maybe I have not searched 
in the right place.

On top of that, I need a positive pulse, 3.5kV, and also a negative 
pulse (600V or so). The can be solved with a transformer.