Re: [neonixie-l] VFD filament drive

['John Rehwinkel' via neonixie-l]

> I wonder why there should be no air gap?

Air gaps lower the inductance, but stabilize it and store energy in the gap.  
Working forward from this, you generally find flyback type circuits use gapped 
cores, and others generally instead opt for best coupling and highest 
inductance.

- John

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Re: [neonixie-l] VFD filament drive

[David Pye]

For mine I used one of those cheap eBay buck converters. 5v in, 1.x v out
(adjustable). 8 iv11 tubes, running for a few years without a blip.

If you needed AC, you could always just use an H bridge and a
microcontroller pin to flip it at a suitable frequency with a smoothing cap.

I found I couldn't have ordered the components cheaper than the finished
eBay module...

David

On Wed, 1 Sep 2021, 14:57 Dekatron42,  wrote:

> You can use airgaps in transformers in some cases but this design should
> be without one according to Ed.
>
> I am using ferrite pot cores in some other designs where they are wound as
> a transformer but where the Q-value is of importance and there I use an
> airgap and also a trimmer through the center to adjust them for a minimum
> Q-value at a certain frequency.
>
> Q-value according to TDK:
> https://product.tdk.com/en/contact/faq/inductors-0003.html and also at
> Wikipedia: https://en.wikipedia.org/wiki/Q_factor
>
> This article explains airgap in inductors/transformers somewhat:
> https://www.linkedin.com/pulse/why-do-we-provide-air-gap-usually-inductor-designs-transformer-p
>
> So sometimes it is a choice depending on design criteria like Q-value and
> material used in the transformer. There are normal laminated transformers
> that use an airgap too, but most mains transformers do not.
>
> /Martin
>
>
>
> On Wednesday, 1 September 2021 at 15:11:31 UTC+2 Paul Andrews wrote:
>
>> Martin,
>>
>> I wonder why there should be no air gap?
>>
>> - Paul
>>
>> On Wednesday, September 1, 2021 at 1:55:30 AM UTC-4 Dekatron42 wrote:
>>
>>> Paul,
>>>
>>> I'll ask him, but a quick search at Digikey showed both some RM10 and
>>> ETD29 cores, but only a few. Finding Ferrite cores today is not easy, I
>>> have searched some for other projects and they aren't usually stocked in
>>> the ranges that the manufacturers make them, and if you want something
>>> outside what is available in stock it becomes very expensive as you'll have
>>> to by thousands if not more. I usually try the ones they have and have to
>>> live with that since I can't buy the thousands needed to get the perfect
>>> one. I'll ask Ed to have a look and see if any of the ones that are stocked
>>> will do - just remember that they will have to be the transformer type
>>> without an airgap between the center pieces to work in this application.
>>>
>>> /Martin
>>>
>>> On Wednesday, 1 September 2021 at 04:26:30 UTC+2 Paul Andrews wrote:
>>>

 Hi Martin

 I tried to find a suitable core at digikey, but their parameters don’t
 map very well to the equation that Ed gives. Could he take a look at what
 they have and perhaps recommend something. For simplicity’s sake I just
 looked at toroids
 https://www.digikey.com/en/products/filter/ferrite-cores/936?s=N4IgTCBcDaICoHsBOCCWATAhgGwAQGNkBTAZxAF0BfIA

 Thanks - Paul
 On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote:

> Since transformers isn't my best area, I only have basic understanding
> of the intricacies but I have experimented some with different 
> transformers
> in different cases like when driving Trochotrons and Dekatrons I decided 
> to
> ask an acquaintance who has worked with transformers. His name is Ed
> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio
> Repair and Restoration forum: https://www.vintage-radio.net/forum/),
> he told me you are welcome to contact him via me so that his email is
> somewhat protected - if you ask him anything related to the
> VFD-drivers it would be kind if you could post something here in this 
> forum
> so we all can learn from it.
>
> This is his answer to my question on what transformer to chose for the
> driver in the article, it sure helped me and I hope it helps anyone who
> wants to experiment with this driver:
>
> "Hi Martin, as it operates about 50/100KHz virtually any ferrite
> should do. It should be a transformer type with no air gap.
> The turns are normally based on the transformer equation for square
> waves
>
> N= V/ 4 * F * B* Ae
>
> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for
> a ferrite, Ae the centre pole area in M^2
>
> The actual losses come out later on in the design process and are not
> part of the initial criteria
>
> Copper sizing is normally based on 3A per mm^2 of cross sectional area
>
> The turns figure he gives looks about right for something like an RM10
> core, or you could try an EE25 or an ETD29 core in sat F44 materials
> ETD's are the core of choice for this type of application and should
> be readily available.
>
> The more turns that are used the lower the iron losses and the cooler
> the core runs, but the copper losses increase unless fatter copper is 
> used.
> Skin effect will be of minor importance at your frequency
>

Re: [neonixie-l] VFD filament drive

[Dekatron42]

You can use airgaps in transformers in some cases but this design should be 
without one according to Ed.

I am using ferrite pot cores in some other designs where they are wound as 
a transformer but where the Q-value is of importance and there I use an 
airgap and also a trimmer through the center to adjust them for a minimum 
Q-value at a certain frequency.

Q-value according to TDK: 
https://product.tdk.com/en/contact/faq/inductors-0003.html and also at 
Wikipedia: https://en.wikipedia.org/wiki/Q_factor

This article explains airgap in inductors/transformers somewhat: 
https://www.linkedin.com/pulse/why-do-we-provide-air-gap-usually-inductor-designs-transformer-p

So sometimes it is a choice depending on design criteria like Q-value and 
material used in the transformer. There are normal laminated transformers 
that use an airgap too, but most mains transformers do not.

/Martin



On Wednesday, 1 September 2021 at 15:11:31 UTC+2 Paul Andrews wrote:

> Martin,
>
> I wonder why there should be no air gap?
>
> - Paul
>
> On Wednesday, September 1, 2021 at 1:55:30 AM UTC-4 Dekatron42 wrote:
>
>> Paul,
>>
>> I'll ask him, but a quick search at Digikey showed both some RM10 and 
>> ETD29 cores, but only a few. Finding Ferrite cores today is not easy, I 
>> have searched some for other projects and they aren't usually stocked in 
>> the ranges that the manufacturers make them, and if you want something 
>> outside what is available in stock it becomes very expensive as you'll have 
>> to by thousands if not more. I usually try the ones they have and have to 
>> live with that since I can't buy the thousands needed to get the perfect 
>> one. I'll ask Ed to have a look and see if any of the ones that are stocked 
>> will do - just remember that they will have to be the transformer type 
>> without an airgap between the center pieces to work in this application.
>>
>> /Martin
>>
>> On Wednesday, 1 September 2021 at 04:26:30 UTC+2 Paul Andrews wrote:
>>
>>>
>>> Hi Martin
>>>
>>> I tried to find a suitable core at digikey, but their parameters don’t 
>>> map very well to the equation that Ed gives. Could he take a look at what 
>>> they have and perhaps recommend something. For simplicity’s sake I just 
>>> looked at toroids 
>>> https://www.digikey.com/en/products/filter/ferrite-cores/936?s=N4IgTCBcDaICoHsBOCCWATAhgGwAQGNkBTAZxAF0BfIA
>>>
>>> Thanks - Paul
>>> On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote:
>>>
 Since transformers isn't my best area, I only have basic understanding 
 of the intricacies but I have experimented some with different 
 transformers 
 in different cases like when driving Trochotrons and Dekatrons I decided 
 to 
 ask an acquaintance who has worked with transformers. His name is Ed 
 Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio 
 Repair and Restoration forum: https://www.vintage-radio.net/forum/), 
 he told me you are welcome to contact him via me so that his email is 
 somewhat protected - if you ask him anything related to the 
 VFD-drivers it would be kind if you could post something here in this 
 forum 
 so we all can learn from it.

 This is his answer to my question on what transformer to chose for the 
 driver in the article, it sure helped me and I hope it helps anyone who 
 wants to experiment with this driver:

 "Hi Martin, as it operates about 50/100KHz virtually any ferrite should 
 do. It should be a transformer type with no air gap.
 The turns are normally based on the transformer equation for square 
 waves

 N= V/ 4 * F * B* Ae

 N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a 
 ferrite, Ae the centre pole area in M^2

 The actual losses come out later on in the design process and are not 
 part of the initial criteria

 Copper sizing is normally based on 3A per mm^2 of cross sectional area

 The turns figure he gives looks about right for something like an RM10 
 core, or you could try an EE25 or an ETD29 core in sat F44 materials 
 ETD's are the core of choice for this type of application and should be 
 readily available.

 The more turns that are used the lower the iron losses and the cooler 
 the core runs, but the copper losses increase unless fatter copper is used.
 Skin effect will be of minor importance at your frequency

 It would also work on a normal laminated core at 50Hz which should not 
 be too big as you can run that at up to 1.5T flux density.
 Regulation could be a normal type of regulator set for constant current.

 Always many choices in Engineering

 Cheers,  Ed

 Ed Dinning Retired Engineer"

 /Martin

 On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote:

> When I have time, I will try the driver at the link Martin gave (
> 

Re: [neonixie-l] VFD filament drive

[Paul Andrews]

Martin,

I wonder why there should be no air gap?

- Paul

On Wednesday, September 1, 2021 at 1:55:30 AM UTC-4 Dekatron42 wrote:

> Paul,
>
> I'll ask him, but a quick search at Digikey showed both some RM10 and 
> ETD29 cores, but only a few. Finding Ferrite cores today is not easy, I 
> have searched some for other projects and they aren't usually stocked in 
> the ranges that the manufacturers make them, and if you want something 
> outside what is available in stock it becomes very expensive as you'll have 
> to by thousands if not more. I usually try the ones they have and have to 
> live with that since I can't buy the thousands needed to get the perfect 
> one. I'll ask Ed to have a look and see if any of the ones that are stocked 
> will do - just remember that they will have to be the transformer type 
> without an airgap between the center pieces to work in this application.
>
> /Martin
>
> On Wednesday, 1 September 2021 at 04:26:30 UTC+2 Paul Andrews wrote:
>
>>
>> Hi Martin
>>
>> I tried to find a suitable core at digikey, but their parameters don’t 
>> map very well to the equation that Ed gives. Could he take a look at what 
>> they have and perhaps recommend something. For simplicity’s sake I just 
>> looked at toroids 
>> https://www.digikey.com/en/products/filter/ferrite-cores/936?s=N4IgTCBcDaICoHsBOCCWATAhgGwAQGNkBTAZxAF0BfIA
>>
>> Thanks - Paul
>> On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote:
>>
>>> Since transformers isn't my best area, I only have basic understanding 
>>> of the intricacies but I have experimented some with different transformers 
>>> in different cases like when driving Trochotrons and Dekatrons I decided to 
>>> ask an acquaintance who has worked with transformers. His name is Ed 
>>> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio 
>>> Repair and Restoration forum: https://www.vintage-radio.net/forum/), he 
>>> told me you are welcome to contact him via me so that his email is somewhat 
>>> protected - if you ask him anything related to the VFD-drivers it would 
>>> be kind if you could post something here in this forum so we all can learn 
>>> from it.
>>>
>>> This is his answer to my question on what transformer to chose for the 
>>> driver in the article, it sure helped me and I hope it helps anyone who 
>>> wants to experiment with this driver:
>>>
>>> "Hi Martin, as it operates about 50/100KHz virtually any ferrite should 
>>> do. It should be a transformer type with no air gap.
>>> The turns are normally based on the transformer equation for square waves
>>>
>>> N= V/ 4 * F * B* Ae
>>>
>>> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a 
>>> ferrite, Ae the centre pole area in M^2
>>>
>>> The actual losses come out later on in the design process and are not 
>>> part of the initial criteria
>>>
>>> Copper sizing is normally based on 3A per mm^2 of cross sectional area
>>>
>>> The turns figure he gives looks about right for something like an RM10 
>>> core, or you could try an EE25 or an ETD29 core in sat F44 materials 
>>> ETD's are the core of choice for this type of application and should be 
>>> readily available.
>>>
>>> The more turns that are used the lower the iron losses and the cooler 
>>> the core runs, but the copper losses increase unless fatter copper is used.
>>> Skin effect will be of minor importance at your frequency
>>>
>>> It would also work on a normal laminated core at 50Hz which should not 
>>> be too big as you can run that at up to 1.5T flux density.
>>> Regulation could be a normal type of regulator set for constant current.
>>>
>>> Always many choices in Engineering
>>>
>>> Cheers,  Ed
>>>
>>> Ed Dinning Retired Engineer"
>>>
>>> /Martin
>>>
>>> On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote:
>>>
 When I have time, I will try the driver at the link Martin gave (
 http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), 
 but without the transformer initially. As far as I can tell, the 
 transformer is just to make the VFD drive isolated so you can pull it up 
 above ground.

>>>

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Re: [neonixie-l] VFD filament drive

[Dekatron42]

Paul,

I'll ask him, but a quick search at Digikey showed both some RM10 and ETD29 
cores, but only a few. Finding Ferrite cores today is not easy, I have 
searched some for other projects and they aren't usually stocked in the 
ranges that the manufacturers make them, and if you want something outside 
what is available in stock it becomes very expensive as you'll have to by 
thousands if not more. I usually try the ones they have and have to live 
with that since I can't buy the thousands needed to get the perfect one. 
I'll ask Ed to have a look and see if any of the ones that are stocked will 
do - just remember that they will have to be the transformer type without 
an airgap between the center pieces to work in this application.

/Martin

On Wednesday, 1 September 2021 at 04:26:30 UTC+2 Paul Andrews wrote:

>
> Hi Martin
>
> I tried to find a suitable core at digikey, but their parameters don’t map 
> very well to the equation that Ed gives. Could he take a look at what they 
> have and perhaps recommend something. For simplicity’s sake I just looked 
> at toroids 
> https://www.digikey.com/en/products/filter/ferrite-cores/936?s=N4IgTCBcDaICoHsBOCCWATAhgGwAQGNkBTAZxAF0BfIA
>
> Thanks - Paul
> On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote:
>
>> Since transformers isn't my best area, I only have basic understanding of 
>> the intricacies but I have experimented some with different transformers in 
>> different cases like when driving Trochotrons and Dekatrons I decided to 
>> ask an acquaintance who has worked with transformers. His name is Ed 
>> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio 
>> Repair and Restoration forum: https://www.vintage-radio.net/forum/), he 
>> told me you are welcome to contact him via me so that his email is somewhat 
>> protected - if you ask him anything related to the VFD-drivers it would 
>> be kind if you could post something here in this forum so we all can learn 
>> from it.
>>
>> This is his answer to my question on what transformer to chose for the 
>> driver in the article, it sure helped me and I hope it helps anyone who 
>> wants to experiment with this driver:
>>
>> "Hi Martin, as it operates about 50/100KHz virtually any ferrite should 
>> do. It should be a transformer type with no air gap.
>> The turns are normally based on the transformer equation for square waves
>>
>> N= V/ 4 * F * B* Ae
>>
>> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a 
>> ferrite, Ae the centre pole area in M^2
>>
>> The actual losses come out later on in the design process and are not 
>> part of the initial criteria
>>
>> Copper sizing is normally based on 3A per mm^2 of cross sectional area
>>
>> The turns figure he gives looks about right for something like an RM10 
>> core, or you could try an EE25 or an ETD29 core in sat F44 materials 
>> ETD's are the core of choice for this type of application and should be 
>> readily available.
>>
>> The more turns that are used the lower the iron losses and the cooler the 
>> core runs, but the copper losses increase unless fatter copper is used.
>> Skin effect will be of minor importance at your frequency
>>
>> It would also work on a normal laminated core at 50Hz which should not be 
>> too big as you can run that at up to 1.5T flux density.
>> Regulation could be a normal type of regulator set for constant current.
>>
>> Always many choices in Engineering
>>
>> Cheers,  Ed
>>
>> Ed Dinning Retired Engineer"
>>
>> /Martin
>>
>> On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote:
>>
>>> When I have time, I will try the driver at the link Martin gave (
>>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but 
>>> without the transformer initially. As far as I can tell, the transformer is 
>>> just to make the VFD drive isolated so you can pull it up above ground.
>>>
>>

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Re: [neonixie-l] VFD filament drive

[Paul Andrews]

Hi Martin

I tried to find a suitable core at digikey, but their parameters don’t map 
very well to the equation that Ed gives. Could he take a look at what they 
have and perhaps recommend something. For simplicity’s sake I just looked 
at toroids 
https://www.digikey.com/en/products/filter/ferrite-cores/936?s=N4IgTCBcDaICoHsBOCCWATAhgGwAQGNkBTAZxAF0BfIA

Thanks - Paul
On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote:

> Since transformers isn't my best area, I only have basic understanding of 
> the intricacies but I have experimented some with different transformers in 
> different cases like when driving Trochotrons and Dekatrons I decided to 
> ask an acquaintance who has worked with transformers. His name is Ed 
> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio 
> Repair and Restoration forum: https://www.vintage-radio.net/forum/), he 
> told me you are welcome to contact him via me so that his email is somewhat 
> protected - if you ask him anything related to the VFD-drivers it would 
> be kind if you could post something here in this forum so we all can learn 
> from it.
>
> This is his answer to my question on what transformer to chose for the 
> driver in the article, it sure helped me and I hope it helps anyone who 
> wants to experiment with this driver:
>
> "Hi Martin, as it operates about 50/100KHz virtually any ferrite should 
> do. It should be a transformer type with no air gap.
> The turns are normally based on the transformer equation for square waves
>
> N= V/ 4 * F * B* Ae
>
> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a 
> ferrite, Ae the centre pole area in M^2
>
> The actual losses come out later on in the design process and are not part 
> of the initial criteria
>
> Copper sizing is normally based on 3A per mm^2 of cross sectional area
>
> The turns figure he gives looks about right for something like an RM10 
> core, or you could try an EE25 or an ETD29 core in sat F44 materials 
> ETD's are the core of choice for this type of application and should be 
> readily available.
>
> The more turns that are used the lower the iron losses and the cooler the 
> core runs, but the copper losses increase unless fatter copper is used.
> Skin effect will be of minor importance at your frequency
>
> It would also work on a normal laminated core at 50Hz which should not be 
> too big as you can run that at up to 1.5T flux density.
> Regulation could be a normal type of regulator set for constant current.
>
> Always many choices in Engineering
>
> Cheers,  Ed
>
> Ed Dinning Retired Engineer"
>
> /Martin
>
> On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote:
>
>> When I have time, I will try the driver at the link Martin gave (
>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but 
>> without the transformer initially. As far as I can tell, the transformer is 
>> just to make the VFD drive isolated so you can pull it up above ground.
>>
>

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Re: [neonixie-l] VFD filament drive

[gregebert]

The amount of ringing is usually load-dependent, and is primarily caused by 
the transformer being non-ideal. Changing the coupling factor from 0.99 to 
0.95 should make quite a difference in the ringing. That wont necessarily 
reflect reality, but it does show you the effect it has. Also, it helps to 
include the DC resistance of the transformer windings.

I'm not a big fan of snubbers because they cause losses, and you need to be 
careful about how much current is going thru the capacitor. When I was 
tweaking the design of the DCDC converter for my NIMO clock, I was getting 
a thermal hot-spot on the snubber. After some careful adjustment of the 
duty-cycle and frequency I was able to reduce the ringing and the heat.

I implemented current-limiting in the drivers by adding a small resistance 
between the source and GND; I think it was about 3 ohms. The exact value is 
determined by the Vgs(on) of the MOSFET, your peak current, and the 
driving-voltage at the gate. Like the duty-cycle optimization, this was 
also done on the bench rather than the simulator.




On Monday, August 30, 2021 at 6:59:42 AM UTC-7 Paul Andrews wrote:

> I created the circuit in LTSpice so I could mess with various components 
> and see how it affects things like frequency and wave form. Rings like 
> crazy, so I added an RC snubber, which seemed to also necessitate tying the 
> primary center tap to ground through a capictor/diode (I don't know if that 
> is an artifact of the way LTSpice works, or something that is actually 
> necessary). I copied this from the LT3999 demo board schematic 
> 
> .
>
> [image: filament_snub.JPG]
> I was wondering about voltage sag with this, as there is no regulation and 
> then re-read your post where Ed Dinning says "Regulation could be a normal 
> type of regulator set for constant current". No idea what one of those 
> might be, and whether he is just referring to the 50Hz solution or not.
>
> On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote:
>
>> Since transformers isn't my best area, I only have basic understanding of 
>> the intricacies but I have experimented some with different transformers in 
>> different cases like when driving Trochotrons and Dekatrons I decided to 
>> ask an acquaintance who has worked with transformers. His name is Ed 
>> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio 
>> Repair and Restoration forum: https://www.vintage-radio.net/forum/), he 
>> told me you are welcome to contact him via me so that his email is somewhat 
>> protected - if you ask him anything related to the VFD-drivers it would 
>> be kind if you could post something here in this forum so we all can learn 
>> from it.
>>
>> This is his answer to my question on what transformer to chose for the 
>> driver in the article, it sure helped me and I hope it helps anyone who 
>> wants to experiment with this driver:
>>
>> "Hi Martin, as it operates about 50/100KHz virtually any ferrite should 
>> do. It should be a transformer type with no air gap.
>> The turns are normally based on the transformer equation for square waves
>>
>> N= V/ 4 * F * B* Ae
>>
>> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a 
>> ferrite, Ae the centre pole area in M^2
>>
>> The actual losses come out later on in the design process and are not 
>> part of the initial criteria
>>
>> Copper sizing is normally based on 3A per mm^2 of cross sectional area
>>
>> The turns figure he gives looks about right for something like an RM10 
>> core, or you could try an EE25 or an ETD29 core in sat F44 materials 
>> ETD's are the core of choice for this type of application and should be 
>> readily available.
>>
>> The more turns that are used the lower the iron losses and the cooler the 
>> core runs, but the copper losses increase unless fatter copper is used.
>> Skin effect will be of minor importance at your frequency
>>
>> It would also work on a normal laminated core at 50Hz which should not be 
>> too big as you can run that at up to 1.5T flux density.
>> Regulation could be a normal type of regulator set for constant current.
>>
>> Always many choices in Engineering
>>
>> Cheers,  Ed
>>
>> Ed Dinning Retired Engineer"
>>
>> /Martin
>>
>> On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote:
>>
>>> When I have time, I will try the driver at the link Martin gave (
>>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but 
>>> without the transformer initially. As far as I can tell, the transformer is 
>>> just to make the VFD drive isolated so you can pull it up above ground.
>>>
>>

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Re: [neonixie-l] VFD filament drive

[Paul Andrews]

I created the circuit in LTSpice so I could mess with various components 
and see how it affects things like frequency and wave form. Rings like 
crazy, so I added an RC snubber, which seemed to also necessitate tying the 
primary center tap to ground through a capictor/diode (I don't know if that 
is an artifact of the way LTSpice works, or something that is actually 
necessary). I copied this from the LT3999 demo board schematic 

.

[image: filament_snub.JPG]
I was wondering about voltage sag with this, as there is no regulation and 
then re-read your post where Ed Dinning says "Regulation could be a normal 
type of regulator set for constant current". No idea what one of those 
might be, and whether he is just referring to the 50Hz solution or not.

On Friday, August 27, 2021 at 8:45:56 AM UTC-4 Dekatron42 wrote:

> Since transformers isn't my best area, I only have basic understanding of 
> the intricacies but I have experimented some with different transformers in 
> different cases like when driving Trochotrons and Dekatrons I decided to 
> ask an acquaintance who has worked with transformers. His name is Ed 
> Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio 
> Repair and Restoration forum: https://www.vintage-radio.net/forum/), he 
> told me you are welcome to contact him via me so that his email is somewhat 
> protected - if you ask him anything related to the VFD-drivers it would 
> be kind if you could post something here in this forum so we all can learn 
> from it.
>
> This is his answer to my question on what transformer to chose for the 
> driver in the article, it sure helped me and I hope it helps anyone who 
> wants to experiment with this driver:
>
> "Hi Martin, as it operates about 50/100KHz virtually any ferrite should 
> do. It should be a transformer type with no air gap.
> The turns are normally based on the transformer equation for square waves
>
> N= V/ 4 * F * B* Ae
>
> N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a 
> ferrite, Ae the centre pole area in M^2
>
> The actual losses come out later on in the design process and are not part 
> of the initial criteria
>
> Copper sizing is normally based on 3A per mm^2 of cross sectional area
>
> The turns figure he gives looks about right for something like an RM10 
> core, or you could try an EE25 or an ETD29 core in sat F44 materials 
> ETD's are the core of choice for this type of application and should be 
> readily available.
>
> The more turns that are used the lower the iron losses and the cooler the 
> core runs, but the copper losses increase unless fatter copper is used.
> Skin effect will be of minor importance at your frequency
>
> It would also work on a normal laminated core at 50Hz which should not be 
> too big as you can run that at up to 1.5T flux density.
> Regulation could be a normal type of regulator set for constant current.
>
> Always many choices in Engineering
>
> Cheers,  Ed
>
> Ed Dinning Retired Engineer"
>
> /Martin
>
> On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote:
>
>> When I have time, I will try the driver at the link Martin gave (
>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but 
>> without the transformer initially. As far as I can tell, the transformer is 
>> just to make the VFD drive isolated so you can pull it up above ground.
>>
>

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Re: [neonixie-l] VFD filament drive

[Dekatron42]

Since transformers isn't my best area, I only have basic understanding of 
the intricacies but I have experimented some with different transformers in 
different cases like when driving Trochotrons and Dekatrons I decided to 
ask an acquaintance who has worked with transformers. His name is Ed 
Dinning, I got to know him over at the UKVRRR forum (UK Vintage Radio 
Repair and Restoration forum: https://www.vintage-radio.net/forum/), he 
told me you are welcome to contact him via me so that his email is somewhat 
protected - if you ask him anything related to the VFD-drivers it would be 
kind if you could post something here in this forum so we all can learn 
from it.

This is his answer to my question on what transformer to chose for the 
driver in the article, it sure helped me and I hope it helps anyone who 
wants to experiment with this driver:

"Hi Martin, as it operates about 50/100KHz virtually any ferrite should do. 
It should be a transformer type with no air gap.
The turns are normally based on the transformer equation for square waves

N= V/ 4 * F * B* Ae

N=turns, V=volts F=frequency,B= flux density, typically 200/250mT for a 
ferrite, Ae the centre pole area in M^2

The actual losses come out later on in the design process and are not part 
of the initial criteria

Copper sizing is normally based on 3A per mm^2 of cross sectional area

The turns figure he gives looks about right for something like an RM10 
core, or you could try an EE25 or an ETD29 core in sat F44 materials 
ETD's are the core of choice for this type of application and should be 
readily available.

The more turns that are used the lower the iron losses and the cooler the 
core runs, but the copper losses increase unless fatter copper is used.
Skin effect will be of minor importance at your frequency

It would also work on a normal laminated core at 50Hz which should not be 
too big as you can run that at up to 1.5T flux density.
Regulation could be a normal type of regulator set for constant current.

Always many choices in Engineering

Cheers,  Ed

Ed Dinning Retired Engineer"

/Martin

On Wednesday, 25 August 2021 at 23:02:48 UTC+2 Paul Andrews wrote:

> When I have time, I will try the driver at the link Martin gave (
> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but 
> without the transformer initially. As far as I can tell, the transformer is 
> just to make the VFD drive isolated so you can pull it up above ground.
>

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Re: [neonixie-l] VFD filament drive

[Bill Notfaded]

Some of the vfd driver chips are what I was looking at initially.

Bill

On Wednesday, August 25, 2021 at 2:02:48 PM UTC-7 Paul Andrews wrote:

> When I have time, I will try the driver at the link Martin gave (
> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but 
> without the transformer initially. As far as I can tell, the transformer is 
> just to make the VFD drive isolated so you can pull it up above ground.
>
> On Wednesday, August 25, 2021 at 4:37:56 PM UTC-4 Bill Notfaded wrote:
>
>> I'm kinda in the same boat Paul... VFD's hasn't really been my thing but 
>> figuring out how to drive some weird ones is a new hobby.  I love your 
>> questions because it helps me figure out what I'm doing as well!
>>
>> Bill
>>
>> On Tuesday, August 24, 2021 at 12:57:53 AM UTC-7 Tomasz Kowalczyk wrote:
>>
>>> Did you try simple PWM? I once tried it, but didn't leave it on for long 
>>> time, so I can't tell if it shortens the tube life or not, but by simple 
>>> logic it shouldn't. For most of the time the cathode will be at the same 
>>> potential. Also it's a nice method of elevating the cathode potential above 
>>> negative segment/grid voltage to get rid of faint glow of off segments.
>>>
>>> poniedziałek, 23 sierpnia 2021 o 20:19:58 UTC+2 gregebert napisał(a):
>>>
 Transformers are not ideal, so even with zero load, they consume  
 inductive current. Most of the energy gets returned to the AC line, but 
 some of it gets dissipated as heat (winding resistance, and hysteresis). 
 This is why unloaded wall transformers still get slightly warm.

 You can measure the magnetizing current with multimeter.


 ---
 Be warned that large transformers will have a startup surge current; I 
 have an isolation transformer in my workshop that can supply 20A/120VAC. 
 It 
 has dual primaries, so I can run it from 120V or 240V. If I try to run it 
 from 120V, even with no load, it almost always pops the 20A breaker for my 
 workbench. So, I use 240V and even then I can hear the wires in the 
 conduit 
 vibrate for an instant when it's energized. 

 If you are worried about blowing the fuse in your multimeter when 
 measuring the magnetizing current, it's good practice to use a variac to 
 increase the line voltage starting from 0 volts into your transformer.

 On Monday, August 23, 2021 at 8:49:01 AM UTC-7 Paul Andrews wrote:

> Thanks Martin,
>
> I'm OK with using a transformer. I would prefer something off the 
> shelf, but perhaps I should just wind my own anyway. Seems like a useful 
> skill to have.
>
> As with a lot of these things, I find that I have a lot of questions. 
> For example, this statement:
>
> "The transformer is 1:1, center-tapped. Since the output is to be 300 
> mA max, the magnetizing current at the input should be no more than 30 
> mA. 
> I will try 10 mA"
>
> First of all, how does he get a 10:1 ratio of output current to 
> 'maximum magnetizing current'. Second, what is 'magnetizing current', 
> does 
> he just mean current through the primary?
>
> Then he introduces terms in equations without defining them - they are 
> probably obvious to the initiated (which I am not unfortunately). For 
> example, Xl in  L = Xl/2/PI/F and Al in  N = (L*1e6/Al)^.5. Then having 
> calculated the required number of turns, he just ignores that and goes 
> with 
> something much larger.
>
> On Friday, August 20, 2021 at 5:51:17 PM UTC-4 Dekatron42 wrote:
>
>> There is a nice article in NutsVolts magazine: 
>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf 
>> where a powerful driver is shown, needs a small transformer but seems to 
>> be 
>> well designed with equations for calculations of the transformer.
>>
>> /Martin
>>
>> On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:
>>
>>> Theres a section on filament driving in my blog here:
>>>
>>> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>>>
>>> *Hannah Mishin*
>>> *  She/her/hers*
>>> 
>>>
>>> *hannahmishin.com* 
>>>
>>>
>>>
>>> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain <
>>> to...@telegraphics.com.au> wrote:
>>>
 On 2021-08-20 12:58 p.m., Paul Andrews wrote:
 > I'm designing a clock for DT-1704 tubes and am stumbling at the 
 filament
 > drive stage. They want 1.6V. I want to power it from 5VDC. ...
 > 

 FWIW I've used LM2575 1A adjustable step down for DC filament 
 voltages
 in that range.

 --Toby

Re: [neonixie-l] VFD filament drive

[Paul Andrews]

When I have time, I will try the driver at the link Martin gave (
http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf), but 
without the transformer initially. As far as I can tell, the transformer is 
just to make the VFD drive isolated so you can pull it up above ground.

On Wednesday, August 25, 2021 at 4:37:56 PM UTC-4 Bill Notfaded wrote:

> I'm kinda in the same boat Paul... VFD's hasn't really been my thing but 
> figuring out how to drive some weird ones is a new hobby.  I love your 
> questions because it helps me figure out what I'm doing as well!
>
> Bill
>
> On Tuesday, August 24, 2021 at 12:57:53 AM UTC-7 Tomasz Kowalczyk wrote:
>
>> Did you try simple PWM? I once tried it, but didn't leave it on for long 
>> time, so I can't tell if it shortens the tube life or not, but by simple 
>> logic it shouldn't. For most of the time the cathode will be at the same 
>> potential. Also it's a nice method of elevating the cathode potential above 
>> negative segment/grid voltage to get rid of faint glow of off segments.
>>
>> poniedziałek, 23 sierpnia 2021 o 20:19:58 UTC+2 gregebert napisał(a):
>>
>>> Transformers are not ideal, so even with zero load, they consume  
>>> inductive current. Most of the energy gets returned to the AC line, but 
>>> some of it gets dissipated as heat (winding resistance, and hysteresis). 
>>> This is why unloaded wall transformers still get slightly warm.
>>>
>>> You can measure the magnetizing current with multimeter.
>>>
>>>
>>> ---
>>> Be warned that large transformers will have a startup surge current; I 
>>> have an isolation transformer in my workshop that can supply 20A/120VAC. It 
>>> has dual primaries, so I can run it from 120V or 240V. If I try to run it 
>>> from 120V, even with no load, it almost always pops the 20A breaker for my 
>>> workbench. So, I use 240V and even then I can hear the wires in the conduit 
>>> vibrate for an instant when it's energized. 
>>>
>>> If you are worried about blowing the fuse in your multimeter when 
>>> measuring the magnetizing current, it's good practice to use a variac to 
>>> increase the line voltage starting from 0 volts into your transformer.
>>>
>>> On Monday, August 23, 2021 at 8:49:01 AM UTC-7 Paul Andrews wrote:
>>>
 Thanks Martin,

 I'm OK with using a transformer. I would prefer something off the 
 shelf, but perhaps I should just wind my own anyway. Seems like a useful 
 skill to have.

 As with a lot of these things, I find that I have a lot of questions. 
 For example, this statement:

 "The transformer is 1:1, center-tapped. Since the output is to be 300 
 mA max, the magnetizing current at the input should be no more than 30 mA. 
 I will try 10 mA"

 First of all, how does he get a 10:1 ratio of output current to 
 'maximum magnetizing current'. Second, what is 'magnetizing current', does 
 he just mean current through the primary?

 Then he introduces terms in equations without defining them - they are 
 probably obvious to the initiated (which I am not unfortunately). For 
 example, Xl in  L = Xl/2/PI/F and Al in  N = (L*1e6/Al)^.5. Then having 
 calculated the required number of turns, he just ignores that and goes 
 with 
 something much larger.

 On Friday, August 20, 2021 at 5:51:17 PM UTC-4 Dekatron42 wrote:

> There is a nice article in NutsVolts magazine: 
> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf 
> where a powerful driver is shown, needs a small transformer but seems to 
> be 
> well designed with equations for calculations of the transformer.
>
> /Martin
>
> On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:
>
>> Theres a section on filament driving in my blog here:
>>
>> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>>
>> *Hannah Mishin*
>> *  She/her/hers*
>> 
>>
>> *hannahmishin.com* 
>>
>>
>>
>> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  
>> wrote:
>>
>>> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
>>> > I'm designing a clock for DT-1704 tubes and am stumbling at the 
>>> filament
>>> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
>>> > 
>>>
>>> FWIW I've used LM2575 1A adjustable step down for DC filament 
>>> voltages
>>> in that range.
>>>
>>> --Toby
>>>
>>>
>>> > ...
>>> > 
>>> > So I would appreciate any suggestions for what direction I should 
>>> take
>>> > here. I have too many options and no clear criteria.
>>> > 
>>> > -- 
>>> > You received this message because you are subscribed to the Google
>>> > Groups 

Re: [neonixie-l] VFD filament drive

[Bill Notfaded]

I also have some  DT-1704 so this is great!  I have two clocks that use 
them as well.

Bill

On Wednesday, August 25, 2021 at 1:37:56 PM UTC-7 Bill Notfaded wrote:

> I'm kinda in the same boat Paul... VFD's hasn't really been my thing but 
> figuring out how to drive some weird ones is a new hobby.  I love your 
> questions because it helps me figure out what I'm doing as well!
>
> Bill
>
> On Tuesday, August 24, 2021 at 12:57:53 AM UTC-7 Tomasz Kowalczyk wrote:
>
>> Did you try simple PWM? I once tried it, but didn't leave it on for long 
>> time, so I can't tell if it shortens the tube life or not, but by simple 
>> logic it shouldn't. For most of the time the cathode will be at the same 
>> potential. Also it's a nice method of elevating the cathode potential above 
>> negative segment/grid voltage to get rid of faint glow of off segments.
>>
>> poniedziałek, 23 sierpnia 2021 o 20:19:58 UTC+2 gregebert napisał(a):
>>
>>> Transformers are not ideal, so even with zero load, they consume  
>>> inductive current. Most of the energy gets returned to the AC line, but 
>>> some of it gets dissipated as heat (winding resistance, and hysteresis). 
>>> This is why unloaded wall transformers still get slightly warm.
>>>
>>> You can measure the magnetizing current with multimeter.
>>>
>>>
>>> ---
>>> Be warned that large transformers will have a startup surge current; I 
>>> have an isolation transformer in my workshop that can supply 20A/120VAC. It 
>>> has dual primaries, so I can run it from 120V or 240V. If I try to run it 
>>> from 120V, even with no load, it almost always pops the 20A breaker for my 
>>> workbench. So, I use 240V and even then I can hear the wires in the conduit 
>>> vibrate for an instant when it's energized. 
>>>
>>> If you are worried about blowing the fuse in your multimeter when 
>>> measuring the magnetizing current, it's good practice to use a variac to 
>>> increase the line voltage starting from 0 volts into your transformer.
>>>
>>> On Monday, August 23, 2021 at 8:49:01 AM UTC-7 Paul Andrews wrote:
>>>
 Thanks Martin,

 I'm OK with using a transformer. I would prefer something off the 
 shelf, but perhaps I should just wind my own anyway. Seems like a useful 
 skill to have.

 As with a lot of these things, I find that I have a lot of questions. 
 For example, this statement:

 "The transformer is 1:1, center-tapped. Since the output is to be 300 
 mA max, the magnetizing current at the input should be no more than 30 mA. 
 I will try 10 mA"

 First of all, how does he get a 10:1 ratio of output current to 
 'maximum magnetizing current'. Second, what is 'magnetizing current', does 
 he just mean current through the primary?

 Then he introduces terms in equations without defining them - they are 
 probably obvious to the initiated (which I am not unfortunately). For 
 example, Xl in  L = Xl/2/PI/F and Al in  N = (L*1e6/Al)^.5. Then having 
 calculated the required number of turns, he just ignores that and goes 
 with 
 something much larger.

 On Friday, August 20, 2021 at 5:51:17 PM UTC-4 Dekatron42 wrote:

> There is a nice article in NutsVolts magazine: 
> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf 
> where a powerful driver is shown, needs a small transformer but seems to 
> be 
> well designed with equations for calculations of the transformer.
>
> /Martin
>
> On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:
>
>> Theres a section on filament driving in my blog here:
>>
>> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>>
>> *Hannah Mishin*
>> *  She/her/hers*
>> 
>>
>> *hannahmishin.com* 
>>
>>
>>
>> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  
>> wrote:
>>
>>> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
>>> > I'm designing a clock for DT-1704 tubes and am stumbling at the 
>>> filament
>>> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
>>> > 
>>>
>>> FWIW I've used LM2575 1A adjustable step down for DC filament 
>>> voltages
>>> in that range.
>>>
>>> --Toby
>>>
>>>
>>> > ...
>>> > 
>>> > So I would appreciate any suggestions for what direction I should 
>>> take
>>> > here. I have too many options and no clear criteria.
>>> > 
>>> > -- 
>>> > You received this message because you are subscribed to the Google
>>> > Groups "neonixie-l" group.
>>> > To unsubscribe from this group and stop receiving emails from it, 
>>> send
>>> > an email to neonixie-l+...@googlegroups.com
>>> > 

Re: [neonixie-l] VFD filament drive

[Bill Notfaded]

I'm kinda in the same boat Paul... VFD's hasn't really been my thing but 
figuring out how to drive some weird ones is a new hobby.  I love your 
questions because it helps me figure out what I'm doing as well!

Bill

On Tuesday, August 24, 2021 at 12:57:53 AM UTC-7 Tomasz Kowalczyk wrote:

> Did you try simple PWM? I once tried it, but didn't leave it on for long 
> time, so I can't tell if it shortens the tube life or not, but by simple 
> logic it shouldn't. For most of the time the cathode will be at the same 
> potential. Also it's a nice method of elevating the cathode potential above 
> negative segment/grid voltage to get rid of faint glow of off segments.
>
> poniedziałek, 23 sierpnia 2021 o 20:19:58 UTC+2 gregebert napisał(a):
>
>> Transformers are not ideal, so even with zero load, they consume  
>> inductive current. Most of the energy gets returned to the AC line, but 
>> some of it gets dissipated as heat (winding resistance, and hysteresis). 
>> This is why unloaded wall transformers still get slightly warm.
>>
>> You can measure the magnetizing current with multimeter.
>>
>>
>> ---
>> Be warned that large transformers will have a startup surge current; I 
>> have an isolation transformer in my workshop that can supply 20A/120VAC. It 
>> has dual primaries, so I can run it from 120V or 240V. If I try to run it 
>> from 120V, even with no load, it almost always pops the 20A breaker for my 
>> workbench. So, I use 240V and even then I can hear the wires in the conduit 
>> vibrate for an instant when it's energized. 
>>
>> If you are worried about blowing the fuse in your multimeter when 
>> measuring the magnetizing current, it's good practice to use a variac to 
>> increase the line voltage starting from 0 volts into your transformer.
>>
>> On Monday, August 23, 2021 at 8:49:01 AM UTC-7 Paul Andrews wrote:
>>
>>> Thanks Martin,
>>>
>>> I'm OK with using a transformer. I would prefer something off the shelf, 
>>> but perhaps I should just wind my own anyway. Seems like a useful skill to 
>>> have.
>>>
>>> As with a lot of these things, I find that I have a lot of questions. 
>>> For example, this statement:
>>>
>>> "The transformer is 1:1, center-tapped. Since the output is to be 300 mA 
>>> max, the magnetizing current at the input should be no more than 30 mA. I 
>>> will try 10 mA"
>>>
>>> First of all, how does he get a 10:1 ratio of output current to 'maximum 
>>> magnetizing current'. Second, what is 'magnetizing current', does he just 
>>> mean current through the primary?
>>>
>>> Then he introduces terms in equations without defining them - they are 
>>> probably obvious to the initiated (which I am not unfortunately). For 
>>> example, Xl in  L = Xl/2/PI/F and Al in  N = (L*1e6/Al)^.5. Then having 
>>> calculated the required number of turns, he just ignores that and goes with 
>>> something much larger.
>>>
>>> On Friday, August 20, 2021 at 5:51:17 PM UTC-4 Dekatron42 wrote:
>>>
 There is a nice article in NutsVolts magazine: 
 http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf 
 where a powerful driver is shown, needs a small transformer but seems to 
 be 
 well designed with equations for calculations of the transformer.

 /Martin

 On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:

> Theres a section on filament driving in my blog here:
>
> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>
> *Hannah Mishin*
> *  She/her/hers*
> 
>
> *hannahmishin.com* 
>
>
>
> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  
> wrote:
>
>> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
>> > I'm designing a clock for DT-1704 tubes and am stumbling at the 
>> filament
>> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
>> > 
>>
>> FWIW I've used LM2575 1A adjustable step down for DC filament voltages
>> in that range.
>>
>> --Toby
>>
>>
>> > ...
>> > 
>> > So I would appreciate any suggestions for what direction I should 
>> take
>> > here. I have too many options and no clear criteria.
>> > 
>> > -- 
>> > You received this message because you are subscribed to the Google
>> > Groups "neonixie-l" group.
>> > To unsubscribe from this group and stop receiving emails from it, 
>> send
>> > an email to neonixie-l+...@googlegroups.com
>> > .
>> > To view this discussion on the web, visit
>> > 
>> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com
>> > <
>> 

Re: [neonixie-l] VFD filament drive

[Tomasz Kowalczyk]

Did you try simple PWM? I once tried it, but didn't leave it on for long 
time, so I can't tell if it shortens the tube life or not, but by simple 
logic it shouldn't. For most of the time the cathode will be at the same 
potential. Also it's a nice method of elevating the cathode potential above 
negative segment/grid voltage to get rid of faint glow of off segments.

poniedziałek, 23 sierpnia 2021 o 20:19:58 UTC+2 gregebert napisał(a):

> Transformers are not ideal, so even with zero load, they consume  
> inductive current. Most of the energy gets returned to the AC line, but 
> some of it gets dissipated as heat (winding resistance, and hysteresis). 
> This is why unloaded wall transformers still get slightly warm.
>
> You can measure the magnetizing current with multimeter.
>
>
> ---
> Be warned that large transformers will have a startup surge current; I 
> have an isolation transformer in my workshop that can supply 20A/120VAC. It 
> has dual primaries, so I can run it from 120V or 240V. If I try to run it 
> from 120V, even with no load, it almost always pops the 20A breaker for my 
> workbench. So, I use 240V and even then I can hear the wires in the conduit 
> vibrate for an instant when it's energized. 
>
> If you are worried about blowing the fuse in your multimeter when 
> measuring the magnetizing current, it's good practice to use a variac to 
> increase the line voltage starting from 0 volts into your transformer.
>
> On Monday, August 23, 2021 at 8:49:01 AM UTC-7 Paul Andrews wrote:
>
>> Thanks Martin,
>>
>> I'm OK with using a transformer. I would prefer something off the shelf, 
>> but perhaps I should just wind my own anyway. Seems like a useful skill to 
>> have.
>>
>> As with a lot of these things, I find that I have a lot of questions. For 
>> example, this statement:
>>
>> "The transformer is 1:1, center-tapped. Since the output is to be 300 mA 
>> max, the magnetizing current at the input should be no more than 30 mA. I 
>> will try 10 mA"
>>
>> First of all, how does he get a 10:1 ratio of output current to 'maximum 
>> magnetizing current'. Second, what is 'magnetizing current', does he just 
>> mean current through the primary?
>>
>> Then he introduces terms in equations without defining them - they are 
>> probably obvious to the initiated (which I am not unfortunately). For 
>> example, Xl in  L = Xl/2/PI/F and Al in  N = (L*1e6/Al)^.5. Then having 
>> calculated the required number of turns, he just ignores that and goes with 
>> something much larger.
>>
>> On Friday, August 20, 2021 at 5:51:17 PM UTC-4 Dekatron42 wrote:
>>
>>> There is a nice article in NutsVolts magazine: 
>>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf where 
>>> a powerful driver is shown, needs a small transformer but seems to be well 
>>> designed with equations for calculations of the transformer.
>>>
>>> /Martin
>>>
>>> On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:
>>>
 Theres a section on filament driving in my blog here:

 https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock

 *Hannah Mishin*
 *  She/her/hers*
 

 *hannahmishin.com* 



 On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  
 wrote:

> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
> > I'm designing a clock for DT-1704 tubes and am stumbling at the 
> filament
> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
> > 
>
> FWIW I've used LM2575 1A adjustable step down for DC filament voltages
> in that range.
>
> --Toby
>
>
> > ...
> > 
> > So I would appreciate any suggestions for what direction I should 
> take
> > here. I have too many options and no clear criteria.
> > 
> > -- 
> > You received this message because you are subscribed to the Google
> > Groups "neonixie-l" group.
> > To unsubscribe from this group and stop receiving emails from it, 
> send
> > an email to neonixie-l+...@googlegroups.com
> > .
> > To view this discussion on the web, visit
> > 
> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com
> > <
> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com?utm_medium=email_source=footer
> >.
>
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> 

Re: [neonixie-l] VFD filament drive

[gregebert]

Transformers are not ideal, so even with zero load, they consume  inductive 
current. Most of the energy gets returned to the AC line, but some of it 
gets dissipated as heat (winding resistance, and hysteresis). This is why 
unloaded wall transformers still get slightly warm.

You can measure the magnetizing current with multimeter.

---
Be warned that large transformers will have a startup surge current; I have 
an isolation transformer in my workshop that can supply 20A/120VAC. It has 
dual primaries, so I can run it from 120V or 240V. If I try to run it from 
120V, even with no load, it almost always pops the 20A breaker for my 
workbench. So, I use 240V and even then I can hear the wires in the conduit 
vibrate for an instant when it's energized. 

If you are worried about blowing the fuse in your multimeter when measuring 
the magnetizing current, it's good practice to use a variac to increase the 
line voltage starting from 0 volts into your transformer.

On Monday, August 23, 2021 at 8:49:01 AM UTC-7 Paul Andrews wrote:

> Thanks Martin,
>
> I'm OK with using a transformer. I would prefer something off the shelf, 
> but perhaps I should just wind my own anyway. Seems like a useful skill to 
> have.
>
> As with a lot of these things, I find that I have a lot of questions. For 
> example, this statement:
>
> "The transformer is 1:1, center-tapped. Since the output is to be 300 mA 
> max, the magnetizing current at the input should be no more than 30 mA. I 
> will try 10 mA"
>
> First of all, how does he get a 10:1 ratio of output current to 'maximum 
> magnetizing current'. Second, what is 'magnetizing current', does he just 
> mean current through the primary?
>
> Then he introduces terms in equations without defining them - they are 
> probably obvious to the initiated (which I am not unfortunately). For 
> example, Xl in  L = Xl/2/PI/F and Al in  N = (L*1e6/Al)^.5. Then having 
> calculated the required number of turns, he just ignores that and goes with 
> something much larger.
>
> On Friday, August 20, 2021 at 5:51:17 PM UTC-4 Dekatron42 wrote:
>
>> There is a nice article in NutsVolts magazine: 
>> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf where 
>> a powerful driver is shown, needs a small transformer but seems to be well 
>> designed with equations for calculations of the transformer.
>>
>> /Martin
>>
>> On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:
>>
>>> Theres a section on filament driving in my blog here:
>>>
>>> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>>>
>>> *Hannah Mishin*
>>> *  She/her/hers*
>>> 
>>>
>>> *hannahmishin.com* 
>>>
>>>
>>>
>>> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  
>>> wrote:
>>>
 On 2021-08-20 12:58 p.m., Paul Andrews wrote:
 > I'm designing a clock for DT-1704 tubes and am stumbling at the 
 filament
 > drive stage. They want 1.6V. I want to power it from 5VDC. ...
 > 

 FWIW I've used LM2575 1A adjustable step down for DC filament voltages
 in that range.

 --Toby


 > ...
 > 
 > So I would appreciate any suggestions for what direction I should take
 > here. I have too many options and no clear criteria.
 > 
 > -- 
 > You received this message because you are subscribed to the Google
 > Groups "neonixie-l" group.
 > To unsubscribe from this group and stop receiving emails from it, send
 > an email to neonixie-l+...@googlegroups.com
 > .
 > To view this discussion on the web, visit
 > 
 https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com
 > <
 https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com?utm_medium=email_source=footer
 >.

 -- 
 You received this message because you are subscribed to the Google 
 Groups "neonixie-l" group.

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 an email to neonixie-l+...@googlegroups.com.
 To view this discussion on the web, visit 
 https://groups.google.com/d/msgid/neonixie-l/ce44816f-120e-abae-060f-fe062d24f836%40telegraphics.com.au
 .

>>>

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Re: [neonixie-l] VFD filament drive

[Paul Andrews]

Thanks Martin,

I'm OK with using a transformer. I would prefer something off the shelf, 
but perhaps I should just wind my own anyway. Seems like a useful skill to 
have.

As with a lot of these things, I find that I have a lot of questions. For 
example, this statement:

"The transformer is 1:1, center-tapped. Since the output is to be 300 mA 
max, the magnetizing current at the input should be no more than 30 mA. I 
will try 10 mA"

First of all, how does he get a 10:1 ratio of output current to 'maximum 
magnetizing current'. Second, what is 'magnetizing current', does he just 
mean current through the primary?

Then he introduces terms in equations without defining them - they are 
probably obvious to the initiated (which I am not unfortunately). For 
example, Xl in  L = Xl/2/PI/F and Al in  N = (L*1e6/Al)^.5. Then having 
calculated the required number of turns, he just ignores that and goes with 
something much larger.

On Friday, August 20, 2021 at 5:51:17 PM UTC-4 Dekatron42 wrote:

> There is a nice article in NutsVolts magazine: 
> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf where a 
> powerful driver is shown, needs a small transformer but seems to be well 
> designed with equations for calculations of the transformer.
>
> /Martin
>
> On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:
>
>> Theres a section on filament driving in my blog here:
>>
>> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>>
>> *Hannah Mishin*
>> *  She/her/hers*
>> 
>>
>> *hannahmishin.com* 
>>
>>
>>
>> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  
>> wrote:
>>
>>> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
>>> > I'm designing a clock for DT-1704 tubes and am stumbling at the 
>>> filament
>>> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
>>> > 
>>>
>>> FWIW I've used LM2575 1A adjustable step down for DC filament voltages
>>> in that range.
>>>
>>> --Toby
>>>
>>>
>>> > ...
>>> > 
>>> > So I would appreciate any suggestions for what direction I should take
>>> > here. I have too many options and no clear criteria.
>>> > 
>>> > -- 
>>> > You received this message because you are subscribed to the Google
>>> > Groups "neonixie-l" group.
>>> > To unsubscribe from this group and stop receiving emails from it, send
>>> > an email to neonixie-l+...@googlegroups.com
>>> > .
>>> > To view this discussion on the web, visit
>>> > 
>>> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com
>>> > <
>>> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com?utm_medium=email_source=footer
>>> >.
>>>
>>> -- 
>>> You received this message because you are subscribed to the Google 
>>> Groups "neonixie-l" group.
>>>
>> To unsubscribe from this group and stop receiving emails from it, send an 
>>> email to neonixie-l+...@googlegroups.com.
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>>> https://groups.google.com/d/msgid/neonixie-l/ce44816f-120e-abae-060f-fe062d24f836%40telegraphics.com.au
>>> .
>>>
>>

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Re: [neonixie-l] VFD filament drive

['John Rehwinkel' via neonixie-l]

> 
> I'm designing a clock for DT-1704 tubes and am stumbling at the filament 
> drive stage. They want 1.6V. I want to power it from 5VDC. I've tried wiring 
> them in series, but there is a noticeable brightness gradient if I do.

I'm a big fan of series resistors (one per tube).  It's inefficient, but low 
parts count, and gives a soft start to the filament.  Another approach is 
current regulators or the aforementioned AC drive with a capacitive dropper.

- John

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Re: [neonixie-l] VFD filament drive

[Adrian Godwin]

I mean to try this on a device I'm building, but won't an H-bridge driver
do ?

It will provide an average potential of half the drive voltage giving the
ability to place a grid or anode at a small negative potential, and if the
filament requirement is less than the easy 5V it can be reduced using PWM
by floating the H-bridge. Higher or lower average acceleration voltages can
be accommodated by setting both ends of the filament to 0 or 5 during the
off-period
.


On Fri, Aug 20, 2021 at 10:51 PM Dekatron42 
wrote:

> There is a nice article in NutsVolts magazine:
> http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf where a
> powerful driver is shown, needs a small transformer but seems to be well
> designed with equations for calculations of the transformer.
>
> /Martin
>
> On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:
>
>> Theres a section on filament driving in my blog here:
>>
>> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>>
>> *Hannah Mishin*
>> *  She/her/hers*
>> 
>>
>> *hannahmishin.com* 
>>
>>
>>
>> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain 
>> wrote:
>>
>>> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
>>> > I'm designing a clock for DT-1704 tubes and am stumbling at the
>>> filament
>>> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
>>> >
>>>
>>> FWIW I've used LM2575 1A adjustable step down for DC filament voltages
>>> in that range.
>>>
>>> --Toby
>>>
>>>
>>> > ...
>>> >
>>> > So I would appreciate any suggestions for what direction I should take
>>> > here. I have too many options and no clear criteria.
>>> >
>>> > --
>>> > You received this message because you are subscribed to the Google
>>> > Groups "neonixie-l" group.
>>> > To unsubscribe from this group and stop receiving emails from it, send
>>> > an email to neonixie-l+...@googlegroups.com
>>> > .
>>> > To view this discussion on the web, visit
>>> >
>>> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com
>>> > <
>>> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com?utm_medium=email_source=footer
>>> >.
>>>
>>> --
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>>> email to neonixie-l+...@googlegroups.com.
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>>> https://groups.google.com/d/msgid/neonixie-l/ce44816f-120e-abae-060f-fe062d24f836%40telegraphics.com.au
>>> .
>>>
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Re: [neonixie-l] VFD filament drive

[Dekatron42]

There is a nice article in NutsVolts magazine: 
http://www.nutsvolts.com/media-files/Forum-Articles/QA_201110.pdf where a 
powerful driver is shown, needs a small transformer but seems to be well 
designed with equations for calculations of the transformer.

/Martin

On Friday, 20 August 2021 at 21:37:46 UTC+2 Hannah Mishin wrote:

> Theres a section on filament driving in my blog here:
>
> https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock
>
> *Hannah Mishin*
> *  She/her/hers*
> 
>
> *hannahmishin.com* 
>
>
>
> On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  
> wrote:
>
>> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
>> > I'm designing a clock for DT-1704 tubes and am stumbling at the filament
>> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
>> > 
>>
>> FWIW I've used LM2575 1A adjustable step down for DC filament voltages
>> in that range.
>>
>> --Toby
>>
>>
>> > ...
>> > 
>> > So I would appreciate any suggestions for what direction I should take
>> > here. I have too many options and no clear criteria.
>> > 
>> > -- 
>> > You received this message because you are subscribed to the Google
>> > Groups "neonixie-l" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> > an email to neonixie-l+...@googlegroups.com
>> > .
>> > To view this discussion on the web, visit
>> > 
>> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com
>> > <
>> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com?utm_medium=email_source=footer
>> >.
>>
>> -- 
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>> https://groups.google.com/d/msgid/neonixie-l/ce44816f-120e-abae-060f-fe062d24f836%40telegraphics.com.au
>> .
>>
>

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Re: [neonixie-l] VFD filament drive

[Hannah Mishin]

Theres a section on filament driving in my blog here:
https://hannahmishin.com/blog/2017/4/30/russian-tri-color-vfd-indicator-clock

*Hannah Mishin*
*  She/her/hers*


*hannahmishin.com* 



On Fri, Aug 20, 2021 at 1:48 PM Toby Thain  wrote:

> On 2021-08-20 12:58 p.m., Paul Andrews wrote:
> > I'm designing a clock for DT-1704 tubes and am stumbling at the filament
> > drive stage. They want 1.6V. I want to power it from 5VDC. ...
> >
>
> FWIW I've used LM2575 1A adjustable step down for DC filament voltages
> in that range.
>
> --Toby
>
>
> > ...
> >
> > So I would appreciate any suggestions for what direction I should take
> > here. I have too many options and no clear criteria.
> >
> > --
> > You received this message because you are subscribed to the Google
> > Groups "neonixie-l" group.
> > To unsubscribe from this group and stop receiving emails from it, send
> > an email to neonixie-l+unsubscr...@googlegroups.com
> > .
> > To view this discussion on the web, visit
> >
> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com
> > <
> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com?utm_medium=email_source=footer
> >.
>
> --
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> https://groups.google.com/d/msgid/neonixie-l/ce44816f-120e-abae-060f-fe062d24f836%40telegraphics.com.au
> .
>

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Re: [neonixie-l] VFD filament drive

[Toby Thain]

On 2021-08-20 12:58 p.m., Paul Andrews wrote:
> I'm designing a clock for DT-1704 tubes and am stumbling at the filament
> drive stage. They want 1.6V. I want to power it from 5VDC. ...
> 

FWIW I've used LM2575 1A adjustable step down for DC filament voltages
in that range.

--Toby


> ...
> 
> So I would appreciate any suggestions for what direction I should take
> here. I have too many options and no clear criteria.
> 
> -- 
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> .

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Re: [neonixie-l] VFD filament drive

[gregebert]

I used a 2.5VAC transformer for my NIMO clock, and use series dropping 
resistors to get the correct current. Those filaments run at 1.1 VAC and 
200mA. Using AC cancels-out the brightness quirks when using DC. The series 
resistor will reduce the power-on current surge and therefore extend the 
filament life, at the expense of added power. Finally, at least with the 
NIMO tubes, I have individual series fuses, along with logic and software 
to monitor the condition of the filaments, resistors, and fuses [yeah, 
yeah, it's overkill, but I had a lot of fun designing it]

I do have several VFDs waiting for me to design clocks for them...just need 
the time.

On Friday, August 20, 2021 at 10:01:27 AM UTC-7 tntm...@gmail.com wrote:

> Sorry for not being helpful, but I'd love to see your digivac clock when 
> you're done!
>
> On Fri, Aug 20, 2021, 12:58 PM Paul Andrews  wrote:
>
>> I'm designing a clock for DT-1704 tubes and am stumbling at the filament 
>> drive stage. They want 1.6V. I want to power it from 5VDC. I've tried 
>> wiring them in series, but there is a noticeable brightness gradient if I 
>> do. I've tried powering them using a LM4871 to generate a square wave with 
>> 1.6V RMS, but the voltage drops as I add more tubes in parallel (an aside: 
>> why is this? I know it is specified to drive a 4 Ohm to 8 Ohm load, so I 
>> assume that is it). I don't want to dump a bunch of heat through a LDO or a 
>> stack of diodes. So I looked at making a buck converter.
>>
>> If at all possible I would like to re-use the design for other VFDs, e.g 
>> for VFDs that want a grid to be pulled below the VFD voltage, and I would 
>> really prefer to use AC rather DC so I can use it for multi-digit VFD tubes.
>>
>> I thought that if I made the buck converter output isolated I would end 
>> up with a solution that would be more re-usable for different kinds of 
>> VFDs, but naturally I hit the issue of what off-the-shelf transformer I 
>> could use. I also got to thinking that the output diode of a buck converter 
>> that produces 1.6V is going to drop a significant part of the total 
>> voltage, which made me wonder why I should even try to rectify and smooth 
>> the output given that an AC filament voltage would be better anyway. Then I 
>> also wondered if such a solution would hit the same problem as the LM4871 
>> design, i.e. dropping voltage as I add more tubes in parallel.
>>
>> So I would appreciate any suggestions for what direction I should take 
>> here. I have too many options and no clear criteria.
>>
>> -- 
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>> "neonixie-l" group.
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Re: [neonixie-l] VFD filament drive

[Audrey]

Sorry for not being helpful, but I'd love to see your digivac clock when
you're done!

On Fri, Aug 20, 2021, 12:58 PM Paul Andrews  wrote:

> I'm designing a clock for DT-1704 tubes and am stumbling at the filament
> drive stage. They want 1.6V. I want to power it from 5VDC. I've tried
> wiring them in series, but there is a noticeable brightness gradient if I
> do. I've tried powering them using a LM4871 to generate a square wave with
> 1.6V RMS, but the voltage drops as I add more tubes in parallel (an aside:
> why is this? I know it is specified to drive a 4 Ohm to 8 Ohm load, so I
> assume that is it). I don't want to dump a bunch of heat through a LDO or a
> stack of diodes. So I looked at making a buck converter.
>
> If at all possible I would like to re-use the design for other VFDs, e.g
> for VFDs that want a grid to be pulled below the VFD voltage, and I would
> really prefer to use AC rather DC so I can use it for multi-digit VFD tubes.
>
> I thought that if I made the buck converter output isolated I would end up
> with a solution that would be more re-usable for different kinds of VFDs,
> but naturally I hit the issue of what off-the-shelf transformer I could
> use. I also got to thinking that the output diode of a buck converter that
> produces 1.6V is going to drop a significant part of the total voltage,
> which made me wonder why I should even try to rectify and smooth the output
> given that an AC filament voltage would be better anyway. Then I also
> wondered if such a solution would hit the same problem as the LM4871
> design, i.e. dropping voltage as I add more tubes in parallel.
>
> So I would appreciate any suggestions for what direction I should take
> here. I have too many options and no clear criteria.
>
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[neonixie-l] VFD filament drive

[Paul Andrews]

I'm designing a clock for DT-1704 tubes and am stumbling at the filament 
drive stage. They want 1.6V. I want to power it from 5VDC. I've tried 
wiring them in series, but there is a noticeable brightness gradient if I 
do. I've tried powering them using a LM4871 to generate a square wave with 
1.6V RMS, but the voltage drops as I add more tubes in parallel (an aside: 
why is this? I know it is specified to drive a 4 Ohm to 8 Ohm load, so I 
assume that is it). I don't want to dump a bunch of heat through a LDO or a 
stack of diodes. So I looked at making a buck converter.

If at all possible I would like to re-use the design for other VFDs, e.g 
for VFDs that want a grid to be pulled below the VFD voltage, and I would 
really prefer to use AC rather DC so I can use it for multi-digit VFD tubes.

I thought that if I made the buck converter output isolated I would end up 
with a solution that would be more re-usable for different kinds of VFDs, 
but naturally I hit the issue of what off-the-shelf transformer I could 
use. I also got to thinking that the output diode of a buck converter that 
produces 1.6V is going to drop a significant part of the total voltage, 
which made me wonder why I should even try to rectify and smooth the output 
given that an AC filament voltage would be better anyway. Then I also 
wondered if such a solution would hit the same problem as the LM4871 
design, i.e. dropping voltage as I add more tubes in parallel.

So I would appreciate any suggestions for what direction I should take 
here. I have too many options and no clear criteria.

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