On 26/04/2024 7:40 am, John Larkin wrote:
> 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

If you believe that, you will believe anything. This looks like the
usual bankrupt stock retailer - they get stuff they don't know much
about from businesses that have gone bust, and try to sell it.

--
Bill Sloman, Sydney

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.
>
>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.
>
>> 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.

One of the earliest comprehensive studies of ferrite material apps.
There's an electronic version of the first edition on line, for
those interested.

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

RL

On Thu, 25 Apr 2024 22:28:54 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

>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

1600V is a proof test voltage for the part - not a continuos rating.

If your application is a CCFL one, then go for it. That's COTS.

If it requires a continuos high voltage, you will need to take
extra precautions.

RL

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

For the price, these would all be fair exercises in 'why you can't
do that'.

Applications requiring temporary high voltages, particularly those
feeding 'spark gaps', are basically protected by the load.

Physical separation of primary and secondary, reinforced by layered
core insulation (automatic doubling) and filled gaps are basic
techniques of achieving higher proof withstand voltage stress
capabilities.

I'm past slagging Chinese product. They deliver - We don't.

RL

RL

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.
>
>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.

https://archive.org/details/SNELLING__SOFT-FERRITES__1969/page/n13/mode/2up?view=theater

RL

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

On Fri, 26 Apr 2024 00:49:52 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

>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.

Oh.

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.
>

Measurement:

https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png

FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected
capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF

On Sat, 27 Apr 2024 02:17:23 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

>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.
>>
>
>Measurement:
>
>https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png
>
>FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected
>capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF

Leakage inductance?

On 27/04/2024 12:34 pm, John Larkin wrote:
> On Sat, 27 Apr 2024 02:17:23 +0200, Klaus Vestergaard Kragelund
> <klauskvik@hotmail.com> wrote:
>
>> 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.
>>>
>>
>> Measurement:
>>
>> https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png
>>
>> FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected
>> capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF
>
> Leakage inductance?]

Wrong question. What you care about is the coupling between the primary
inductance (which you drive) and the secondary inductances (from which
you take your output). This can vary from 0.98 to about 0.999 in
practical transformers.

The usual way of measuring it is to short one winding and measure the
apparent inductance of the other, but this doesn't allow for resistive
loses in either winding.

If you know the winding resistances you can correct for it.
Sophisticated users presumably do this. I wasn't all that sophisticated
when I did it, and didn't bother.

You can document the measured inductance with the other winding shorted
as the "leakage inductance" but it creates a misleading impression about
what it going on.

And you will write down a much higher leakage inductance if you short a
primary with a only a few turns and measure a secondary with a lot of
turns than when you go the other way, when both measurements reflect the
same mutual coupling.

--
Bill Sloman, Sydney

On 27/04/2024 10:17 am, Klaus Vestergaard Kragelund wrote:
> 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.
>>
>
> Measurement:
>
> https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png
>
> FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected
> capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF

There's no "reflection" involved. The resonance reflects the oscillating
flux in the core, and the parallel capacitances of the primary and
secondary windings both get charged up and discharged during the cycle.

The parallel capacitance of the secondary will be higher, and the
voltages across it much higher, so it is dominant.

The resonant current is flowing through the capacitances so may not heat
the insides of the winding wires.

Measuring the self-heating of a transformer being resonated might be an
interesting exercise.

--
Bill Sloman, Sydney

On Fri, 26 Apr 2024 10:24:36 -0400, legg <legg@nospam.magma.ca> wrote:

>On Fri, 26 Apr 2024 01:36:06 +1000, Bill Sloman <bill.sloman@ieee.org>
<snip>
>>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.
>
Anyone depending on library access these days will be sorely
disappointed.

Can't even enter the Sanford Fleming these days without electronic
verification that you're a paid-up local student or researcher.

Used to be able to just walk in, buy photocopier time and have
at it.

The usefull journals are no longer kept in physical stacks, for
the simple physical browser, either.

RL

On 27-04-2024 08:18, Bill Sloman wrote:
> On 27/04/2024 10:17 am, Klaus Vestergaard Kragelund wrote:
>> 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.
>>>
>>
>> Measurement:
>>
>> https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png
>>
>> FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected
>> capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF
>
> There's no "reflection" involved. The resonance reflects the oscillating
> flux in the core, and the parallel capacitances of the primary and
> secondary windings both get charged up and discharged during the cycle.
>
> The parallel capacitance of the secondary will be higher, and the
> voltages across it much higher, so it is dominant.
>
> The resonant current is flowing through the capacitances so may not heat
> the insides of the winding wires.
>
> Measuring the self-heating of a transformer being resonated might be an
> interesting exercise.
>

I wrote "reflected", since the inductance on the primary was the
measurement. The resonance of the transformer is the same on all
windings, if the coupling is reasonable good.

So like you wrote, the secondary is dominant, which is why the primary
resonance is due to reflection from the secondary.

On Sat, 27 Apr 2024 01:26:09 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>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.

I believe it was Janson, Barrow and Burgum, with Jongsma at Philips
(Mullard), who reorganized Snelling's math into useful off-the-cuff
expressions in the mid 70s. . . using the Steinmetz coefficients etc.

E.A.B. 32 through 34 are typical, if my records are accurate.

The Seimens catalog notes for use of power ferrite graphs 'sort of'
did the same, without actually explicitly stating ANY of them.
They were free and in book form.

Anyways, high voltage applications are a different book.

RL

On Thu, 25 Apr 2024 09:56:21 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> 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 expect that you can't push a decent-looking pulse through a CCFL
transformer. Look at the pics on the Coilcraft page. Those things are
probably designed to have a huge leakage inductance. That makes sense,
since gas tubes are negative resistances.

Of course, we don't know what kind of pulses you need.

Some sort of Marx generator would be fun.

My Pockels Cell driver uses a resonant boost thing with a SiC fet. It
goes from 48v to 1400v in one step.

https://www.highlandtechnology.com/Product/T850

On 27-04-2024 19:17, legg wrote:
> On Sat, 27 Apr 2024 01:26:09 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
>
>> 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.
>
> I believe it was Janson, Barrow and Burgum, with Jongsma at Philips
> (Mullard), who reorganized Snelling's math into useful off-the-cuff
> expressions in the mid 70s. . . using the Steinmetz coefficients etc.
>
> E.A.B. 32 through 34 are typical, if my records are accurate.
>
> The Seimens catalog notes for use of power ferrite graphs 'sort of'
> did the same, without actually explicitly stating ANY of them.
> They were free and in book form.
>
> Anyways, high voltage applications are a different book.
>
Speaking of a book, I have yet to find a book on HV SMPS design....

On 28/04/2024 3:17 am, legg wrote:
> On Sat, 27 Apr 2024 01:26:09 +1000, Bill Sloman <bill.sloman@ieee.org wrote:
>> 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:

>>>> 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.
>
> I believe it was Janson, Barrow and Burgum, with Jongsma at Philips
> (Mullard), who reorganized Snelling's math into useful off-the-cuff
> expressions in the mid 70s. . . using the Steinmetz coefficients etc.
>
> E.A.B. 32 through 34 are typical, if my records are accurate.

Never got to see any of that.
>
> The Seimens catalog notes for use of power ferrite graphs 'sort of'
> did the same, without actually explicitly stating ANY of them.
> They were free and in book form.
>
> Anyways, high voltage applications are a different book.

Why? The ferrites never get to see the high voltages.

The windings do. When I was a graduate student I got to know a guy -
Ales Strojnik - who had come from Slovenia to Melbourne to build a 600kV
scanning transmission microscope,and immersed his winding in liquid
transformer oil. Sulphur hexafluoride gas was more popular but made for
a bulkier system.

https://en.wikipedia.org/wiki/Ale%C5%A1_Strojnik

He was rude about the French higher voltage version, which was huge.

--
Bill Sloman, Sydney

On 28/04/2024 2:49 am, Klaus Vestergaard Kragelund wrote:
> On 27-04-2024 08:18, Bill Sloman wrote:
>> On 27/04/2024 10:17 am, Klaus Vestergaard Kragelund wrote:
>>> 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.
>>>>
>>>
>>> Measurement:
>>>
>>> https://www.electronicsdesign.dk/tmp/FL2015-4D_primaryL.png
>>>
>>> FL2015-4D, primary inductance is 43uH. Resonance is 332kHz, reflected
>>> capacitance to primary is 5nF. Reflected to secondary 100mH is 2.3pF
>>
>> There's no "reflection" involved. The resonance reflects the
>> oscillating flux in the core, and the parallel capacitances of the
>> primary and secondary windings both get charged up and discharged
>> during the cycle.
>>
>> The parallel capacitance of the secondary will be higher, and the
>> voltages across it much higher, so it is dominant.
>>
>> The resonant current is flowing through the capacitances so may not
>> heat the insides of the winding wires.
>>
>> Measuring the self-heating of a transformer being resonated might be
>> an interesting exercise.
>
> I wrote "reflected", since the inductance on the primary was the
> measurement. The resonance of the transformer is the same on all
> windings, if the coupling is reasonable good.
>
> So like you wrote, the secondary is dominant, which is why the primary
> resonance is due to reflection from the secondary.

There's no "reflection" involved. Both the primary and the secondary
winding take part in the same process, and make their own - more or less
independent - contributions.

It's a pedantic point, but getting a proper grip on what going on in
transformer does seem to be difficult, and it does take a while. Getting
close to precisely the right point of view probably helps.

--
Bill Sloman, Sydney

On Sat, 27 Apr 2024 23:51:14 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

>On 27-04-2024 19:17, legg wrote:
>> On Sat, 27 Apr 2024 01:26:09 +1000, Bill Sloman <bill.sloman@ieee.org>
>> wrote:
>>
>>> 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.
>>
>> I believe it was Janson, Barrow and Burgum, with Jongsma at Philips
>> (Mullard), who reorganized Snelling's math into useful off-the-cuff
>> expressions in the mid 70s. . . using the Steinmetz coefficients etc.
>>
>> E.A.B. 32 through 34 are typical, if my records are accurate.
>>
>> The Seimens catalog notes for use of power ferrite graphs 'sort of'
>> did the same, without actually explicitly stating ANY of them.
>> They were free and in book form.
>>
>> Anyways, high voltage applications are a different book.
>>
>Speaking of a book, I have yet to find a book on HV SMPS design....

Books can inspire ideas, but it's more fun (and more profitable) to
invent circuits that aren't in books.

I think it's best to look at the books *after* thinking about the
problem for a few days.

On 29/04/2024 12:00 am, John Larkin wrote:
> On Sat, 27 Apr 2024 23:51:14 +0200, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
>> On 27-04-2024 19:17, legg wrote:
>>> On Sat, 27 Apr 2024 01:26:09 +1000, Bill Sloman <bill.sloman@ieee.org> wrote:
>>>> 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:

<snip>

> Books can inspire ideas, but it's more fun (and more profitable) to
> invent circuits that aren't in books.

Of course most of them don't work, and of those that do work quite a few
have unexpected gotcha's.

> I think it's best to look at the books *after* thinking about the
> problem for a few days.

It's two way street. Think first, so that you have some idea where the
problems are so, that when you do read you are on the look-out for
solutions to those problems, but useful books set you on the track of
problems that you hadn't thought of.

The main problem with innovation is that it is a process of exploration,
and you need to get as much guidance as you can.

Pasteur's comment was that "chance favours the prepared mind".

--
Bill Sloman. Sydney

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

1. AliExpress has a 3.7V to 15 KV transformer plus pcb for C$2.28, delivery
is C$2.78/two weeks :

https://www.aliexpress.com/item/1005001511085929.html

2. A 12V to 15KV High Frequency Power Transformer is C$2.00 and C$2.78
delivery:

https://www.aliexpress.com/item/1005003737611731.html

I ordered both. Delivery was on time, and the parts look to be of high
quality.

3. Amazon has a High Voltage Transformer 3.7V-4.2V to 15KV Boost Step-up
Power Module for C$9.57:

https://www.amazon.ca/Voltage-Transformer-3-7V-4-2V-Step-up-
Generator/dp/B07TR2QFRL/

--
MRM

On 01-05-2024 01:51, Mike Monett VE3BTI wrote:
> 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
>
> 1. AliExpress has a 3.7V to 15 KV transformer plus pcb for C$2.28, delivery
> is C$2.78/two weeks :
>
> https://www.aliexpress.com/item/1005001511085929.html
>
> 2. A 12V to 15KV High Frequency Power Transformer is C$2.00 and C$2.78
> delivery:
>
> https://www.aliexpress.com/item/1005003737611731.html
>
> I ordered both. Delivery was on time, and the parts look to be of high
> quality.
>
> 3. Amazon has a High Voltage Transformer 3.7V-4.2V to 15KV Boost Step-up
> Power Module for C$9.57:
>
> https://www.amazon.ca/Voltage-Transformer-3-7V-4-2V-Step-up-
> Generator/dp/B07TR2QFRL/
>
>
I order some similar ones some weeks ago, still waiting for the mail :-)