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

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

Can you use a C-W multiplier?

For low current, you can do resonant tricks too.

On 24/04/2024 12:25 pm, John Larkin 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
>> step-up 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....
>
> Can you use a C-W multiplier?
>
> For low current, you can do resonant tricks too.

It's easier to use a voltage doubler or tripler that it is to find a
multi-section former off-the shelf. The occasional high voltage power
supply that I've dismantled clearly used proprietary formers, as do the
Coilcraft parts

I suppose one could use self-bonding wire to make a series of
self-supporting pancake windings, but I've never heard of anybody doing it.

The Baxandall configuration is definitely a resonant trick, and copes
with the interwinding capacitance by resonating it with the winding
inductance.

There's nothing "low current" about it, but if you are working at higher
currents and powers you can justify even more elaborate switching
arrangements.

http://sophia-elektronica.com/Baxandall1959JM.pdf

Jim Williams talked about it a lot - application notes AN45, AN49, AN51,
AN55, AN61, AN65 - but described it as a "a current driven Royer
inverter" which is simply wrong.

MOSFETs work better as switches than bipolar transistors, and don't seem
to "squeg".

--
Bill Sloman, Sydney

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

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.

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

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'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.

On 2024-04-24 04:25, John Larkin 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
>
> Can you use a C-W multiplier?
>
> For low current, you can do resonant tricks too.
>

A C-W multiplier gives DC.
I think CCFLs should use AC not DC, to prevent fast blackening of one end.

Arie

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.

I'd look into Pi Winding HV transformers.

..<https://www.edn.com/two-pi-winding/>

Lots of construction details from the Radio Amateur community.

Joe Gwinn

>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 sell CCFLs these days.
>
>Guess I will keep it alive....
>
>Regards
>
>Klaus

Klaus Vestergaard Kragelund <klauskvik@hotmail.com> Wrote in message:r
> HiI 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....RegardsKlaus

Yes, that minimizes the volts per layer, which in turn lowers the
capacitance effect. You can still get custom bobbins to stack
windings like that if you choose to get higher voltages.

Cheers
--

----Android NewsGroup Reader----
https://piaohong.s3-us-west-2.amazonaws.com/usenet/index.html

On 24/04/2024 3:10 pm, Bill Sloman wrote:
> On 24/04/2024 12:25 pm, John Larkin 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
>>> step-up 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....
>>
>> Can you use a C-W multiplier?
>>
>> For low current, you can do resonant tricks too.
>
> It's easier to use a voltage doubler or tripler that it is to find a
> multi-section former off-the shelf. The occasional high voltage power
> supply that I've dismantled clearly used proprietary formers, as do the
> Coilcraft parts
>
> I suppose one could use self-bonding wire to make a series of
> self-supporting pancake windings, but I've never heard of anybody doing it.
>
> The Baxandall configuration is definitely a resonant trick, and copes
> with the interwinding capacitance by resonating it with the winding
> inductance.
>
> There's nothing "low current" about it, but if you are working at higher
> currents and powers you can justify even more elaborate switching
> arrangements.
>
> http://sophia-elektronica.com/Baxandall1959JM.pdf
>
> Jim Williams talked about it a lot - application notes AN45, AN49, AN51,
> AN55, AN61, AN65 - but described it as a "a current driven Royer
> inverter" which is simply wrong.
>
> MOSFETs work better as switches than bipolar transistors, and don't seem
> to "squeg".

The Coilcraft data sheets don't say anything much about the resonant
frequencies of their transformers - except "The FL Series of
transformers is designed for use in cold cathode fluorescent lamp (CCFL)
power supplies at operating frequencies up to 100 kHz" where the "up to
100kHz" gives them a lot of wriggle room.

A primary inductance of around 50uH with a 100:1 step-up implies a 0.5H
secondary inductance. 10pF parallel capacitance would give a 71kHz
resonant frequency, which is less than 100kHz.

Of course once you have one of the Coilcraft parts you can measure the
resonant frequency.

--
Bill Sloman, Sydney

On 24-04-2024 07:10, Bill Sloman wrote:
> On 24/04/2024 12:25 pm, John Larkin 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
>>> step-up 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....
>>
>> Can you use a C-W multiplier?
>>
>> For low current, you can do resonant tricks too.
>
> It's easier to use a voltage doubler or tripler that it is to find a
> multi-section former off-the shelf. The occasional high voltage power
> supply that I've dismantled clearly used proprietary formers, as do the
> Coilcraft parts
>

I am using it for pulse generation, so cannot use a capacitive doubler

> I suppose one could use self-bonding wire to make a series of
> self-supporting pancake windings, but I've never heard of anybody doing it.
>
Yeah, sounds like difficult to do in production

On 25-04-2024 09:02, Bill Sloman wrote:
> On 24/04/2024 3:10 pm, Bill Sloman wrote:
>> On 24/04/2024 12:25 pm, John Larkin 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
>>>> step-up 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....
>>>
>>> Can you use a C-W multiplier?
>>>
>>> For low current, you can do resonant tricks too.
>>
>> It's easier to use a voltage doubler or tripler that it is to find a
>> multi-section former off-the shelf. The occasional high voltage power
>> supply that I've dismantled clearly used proprietary formers, as do
>> the Coilcraft parts
>>
>> I suppose one could use self-bonding wire to make a series of
>> self-supporting pancake windings, but I've never heard of anybody
>> doing it.
>>
>> The Baxandall configuration is definitely a resonant trick, and copes
>> with the interwinding capacitance by resonating it with the winding
>> inductance.
>>
>> There's nothing "low current" about it, but if you are working at
>> higher currents and powers you can justify even more elaborate
>> switching arrangements.
>>
>> http://sophia-elektronica.com/Baxandall1959JM.pdf
>>
>> Jim Williams talked about it a lot - application notes AN45, AN49,
>> AN51, AN55, AN61, AN65 - but described it as a "a current driven Royer
>> inverter" which is simply wrong.
>>
>> MOSFETs work better as switches than bipolar transistors, and don't
>> seem to "squeg".
>
> The Coilcraft data sheets don't say anything much about the resonant
> frequencies of their transformers - except "The FL Series of
> transformers is designed for use in cold cathode fluorescent lamp (CCFL)
> power supplies at operating frequencies up to 100 kHz" where the "up to
> 100kHz" gives them a lot of wriggle room.
>
> A primary inductance of around 50uH with a 100:1 step-up implies a 0.5H
> secondary inductance. 10pF parallel capacitance would give a 71kHz
> resonant frequency, which is less than 100kHz.
>
> Of course once you have one of the Coilcraft parts you can measure the
> resonant frequency.
>
I have ordered some parts, will arrive today and will measure the
resonance frequency. I would expect it to be a lot higher than 100kHz,
but we will see :-)

On 24-04-2024 15:37, 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
>
> 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.
>

Yes, probably better to just wind it with distance between the turns

On 25/04/2024 5:56 pm, Klaus Vestergaard Kragelund wrote:
> On 24-04-2024 07:10, Bill Sloman wrote:
>> On 24/04/2024 12:25 pm, John Larkin 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
>>>> step-up 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....
>>>
>>> Can you use a C-W multiplier?
>>>
>>> For low current, you can do resonant tricks too.
>>
>> It's easier to use a voltage doubler or tripler that it is to find a
>> multi-section former off-the shelf. The occasional high voltage power
>> supply that I've dismantled clearly used proprietary formers, as do
>> the Coilcraft parts
>>
>
> I am using it for pulse generation, so cannot use a capacitive doubler
>
>> I suppose one could use self-bonding wire to make a series of
>> self-supporting pancake windings, but I've never heard of anybody
>> doing it.
>>
> Yeah, sounds like difficult to do in production.

You could print a bunch of them - pairs would be nice for both legs of
the transformer - mount them on a mother board, and feed the U core
halves through the array.

Mechanical stability would be dire, but you could glue on a supporting
structure.

Still messy to put together, but 3.5kV is always difficult to handle.

--
Bill Sloman, Sydney

On 24-04-2024 19:21, Joe Gwinn 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.
>
> I'd look into Pi Winding HV transformers.
>
> .<https://www.edn.com/two-pi-winding/>
>
> Lots of construction details from the Radio Amateur community.
>
Interesting article, thanks.

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.

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.

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'.

RL

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?

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.

--
Bill Sloman, Sydney

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

On 25-04-2024 17:36, Bill Sloman 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.
>
> 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.
>
I have that book. Only found it useful a couple of times...

On 25-04-2024 16:52, 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.
>

Yes, but there will loss associated with the distributed capacitance
between turns, that's why I am trying to reduce that one also

> 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'.
>

I am actually working on an alternative idea, using 2 CCFL transformers,
since as you write they are normally rated for 1600V. Incidentially, the
1600V is the start voltage, runs steady state at 600V.

The idea is to parallel 2 CCFL transformers primary winding, and series
connect the secondary windings. Then connect the center tap to GND, that
way I get -1600V and +1600V, total 3200V without violating the ratings
of the transformer

On 2024-04-25, 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
>
> 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.
>
> 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'.

I see trandformers claimed for 15kV with 6 sections of loose wound
magnet wire. This is however Chinese consumer marketing kilovolts.

https://www.aliexpress.com/item/1005002225061453.html

Given the ~2mm spark gap it suggests something less than 15kV

--
Jasen.
🇺🇦 Слава Україні

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.

On Thu, 25 Apr 2024 21:10:14 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

>On 2024-04-25, 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
>>
>> 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.
>>
>> 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'.
>
>I see trandformers claimed for 15kV with 6 sections of loose wound
>magnet wire. This is however Chinese consumer marketing kilovolts.
>
>https://www.aliexpress.com/item/1005002225061453.html
>
>Given the ~2mm spark gap it suggests something less than 15kV

How dinky. This one is 400 KV.

https://www.amazon.com/AEDIKO-Voltage-Generator-400000V-Transformer/dp/B09L18GG2Z

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.