[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Bill Notfaded]

Mega props for this Paul... I've followed you trials and tribulations in 
hackaday and your posts here.  I've learned a lot from what you've 
documented.  I just want to say thanks and also that it's really 
appreciated.  I wouldn't understand nearly what I do now if it hadn't been 
for your posts.  There's a lot of knowledge out there but if it wasn't for 
people like you that write it down and share what you've found it'd be a 
smaller world.

The transformers from old cameras comment was pretty funny.

B

>

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Richard Arndt]

Interesting point Paul regarding turns ratio.  The PA0367 is 1:12, and even 
though ringing on primary and secondary were small, it was causing havoc 
with devices methods for measuring primary voltage and secondary current.

On Wednesday, May 8, 2019 at 7:45:04 AM UTC-4, Paul Andrews wrote:
>
> I could've sworn I replied to this. Anyway, my design uses an LM3478 and 
> an AO4294 - a combination I have used on many boards with different 
> transformers - and fits on a 17mm diameter board. However driving an IN-18 
> at 155V/6mA the transformer gets very hot! This particular board doesn't do 
> any snubbing on the primary side though.
>
> I have experimented with quite a few different transformers and the design 
> is really quite sensitive to the transformer being used. Interestingly, I 
> have found that a lower winding ratio generally works better I.e. I get 
> better performance with a 1:5 transformer than I do with a 1:10 or a 1:20. 
> I suspect, but can't prove, that this has a lot to do with ringing on the 
> primary, which is worse with the higher ratio transformers.
>
> I also tried one of the LT isolated switches and got nowhere fast with it. 
> One interesting thing about these is that they require a minimum output 
> current draw, something I don't like for a Nixie tube application where you 
> might want to turn the tubes off, and I include dimming in this, where you 
> are turning the tubes off and on very rapidly.
>
>

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Richard Arndt]

Good Point Greg.  The LT3420 has Charge (CHG) pin which is essentially an 
enable/disable.  If CHG=HIGH, device charges to set voltage.  If CHG=HIGH 
and voltage is reached, device enters a refresh mode to regulate.  CHG=LOW 
is low power mode.  CHG can also be PWM'ed by micro to control input 
current to charger.  It has been a year since my last version, and I may 
resurrect working on it cause I'd rather win!  The LT3420 seem quite novel 
in how it measured current/voltage, but there may be a better choice in the 
end.

On Wednesday, May 8, 2019 at 12:16:46 AM UTC-4, gregebert wrote:
>
> Welcome to the club..I've never had a switching supply work exactly as 
> initially conceived. It always took several iterations.
>
> I did not spend much time going thru the datasheet because this device 
> looks like it's meant for pulsed, rather than continuous, operation. That 
> could have a large impact on how it behaves.
>
> First, you will need some scope pictures to get a good idea what's 
> happening in the circuit.
>
>
>

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Paul Andrews]

I could've sworn I replied to this. Anyway, my design uses an LM3478 and an 
AO4294 - a combination I have used on many boards with different transformers - 
and fits on a 17mm diameter board. However driving an IN-18 at 155V/6mA the 
transformer gets very hot! This particular board doesn't do any snubbing on the 
primary side though.

I have experimented with quite a few different transformers and the design is 
really quite sensitive to the transformer being used. Interestingly, I have 
found that a lower winding ratio generally works better I.e. I get better 
performance with a 1:5 transformer than I do with a 1:10 or a 1:20. I suspect, 
but can't prove, that this has a lot to do with ringing on the primary, which 
is worse with the higher ratio transformers.

I also tried one of the LT isolated switches and got nowhere fast with it. One 
interesting thing about these is that they require a minimum output current 
draw, something I don't like for a Nixie tube application where you might want 
to turn the tubes off, and I include dimming in this, where you are turning the 
tubes off and on very rapidly.

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[newxito]

I did some tests with the PA0367 and LT3757 using the datasheet schematic 
(350V/flyback), regulation was ok but the efficiency was poor, 78% at 
5ma/170V with 5V input voltage

Am Mittwoch, 8. Mai 2019 02:18:49 UTC+2 schrieb Richard Arndt:
>
> I've made several PCB design attempts of a small USB 5v to 170v 1w power 
> supply for 1x IN-18 or Dalibor R|Z568M using the PA0367 Transformer 
>  and 
> LT3420 
> .
>   
> Initial design would run away into the 300+ volts unloaded with no sign of 
> regulation when loaded, even though it was set to 170.  After some email 
> advice from Analog Devices looking over my PCB design, paying attention to 
> ground loops, using copper poors for current wires, and vias connecting 
> top/bottom ground planes,  my third attempt regulated @170v to 1ma, but 
> required addition of snubber on secondary.  It would fall out of regulation 
> quickly after 1ma.  I got frustrated, had not ideas left, tossed it into 
> the scrap box...  
>
> If anyone has ideas on how to resurrect this one, I'd work on it and share 
> the design.  Maybe some of the other transformers would be a better 
> choice.  I'd like a small SMD daughter board design costing maybe $10 to 
> incorporate into my OneNixie clocks.  Of course I can buy them on EBay, but 
> that's no fun :-)  I have been using HV supplies from VFDClock's 
> for a few years.  They 
> are quite good!
>
> Rich
>
>
>
> On Thursday, May 2, 2019 at 1:59:20 PM UTC-4, Paul Andrews wrote:
>>
>> One project I have on the back burner is a very small battery-powered 
>> nixie display. I thought that a variation of a power supply design that I 
>> had been using for everything else, would work fine. It turns out that the 
>> prototype of the power supply, which I had built a few years back, only 
>> worked because of a dry solder-joint somewhere on the mosfet (yes, I'm 
>> serious). The version I built specifically for this project quickly had 
>> everything overheating. When I went back and touched up the soldering on 
>> the prototype, it showed the same behavior. The culprit, BTW is pretty much 
>> down to the tiny 1:20 transformer. I have built variations of this design 
>> with bigger transformers that work very well.
>>
>> There are a lot of variations of power supply design that I could mess 
>> with - obviously I have already scoured the internet on this topic - but 
>> that is the trouble. This project will never get finished if I have to run 
>> through multiple prototypes trying to find one that is small enough and 
>> that works. So I was wondering if anyone could just say 'use this design'.
>>
>> The constraints are:
>>
>>1. It has to fit on a circular PCB the same diameter as the tube or 
>>less (about 17mm).
>>2. It has to provide around 150V-160V regulated output, or maybe just 
>>'limited' output.
>>3. It only has to provide 1.5mA to 2mA.
>>4. It has to use a LiPo as the power source, so it should work at 
>>voltages between around 3.5V and 4.5V.
>>5. It has to use parts I can get from digikey (so no sourcing 
>>transformers from old cameras that I can't find for example).
>>
>> Surface mount components are fine...
>>
>

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[gregebert]

Welcome to the club..I've never had a switching supply work exactly as 
initially conceived. It always took several iterations.

I did not spend much time going thru the datasheet because this device 
looks like it's meant for pulsed, rather than continuous, operation. That 
could have a large impact on how it behaves.

First, you will need some scope pictures to get a good idea what's 
happening in the circuit.


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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Paul Andrews]

Hi Greg. I took a look at the transformer you are using, but I opted for 
this one from the same family instead: *LPR6235-253LMRB*. It is 1:10 and 
has a much higher Isat than the one you are using. Amazingly it fit on the 
same footprint and it runs at a cool 100F at room temperature. Very happy.

On Thursday, May 2, 2019 at 1:59:20 PM UTC-4, Paul Andrews wrote:
>
> One project I have on the back burner is a very small battery-powered 
> nixie display. I thought that a variation of a power supply design that I 
> had been using for everything else, would work fine. It turns out that the 
> prototype of the power supply, which I had built a few years back, only 
> worked because of a dry solder-joint somewhere on the mosfet (yes, I'm 
> serious). The version I built specifically for this project quickly had 
> everything overheating. When I went back and touched up the soldering on 
> the prototype, it showed the same behavior. The culprit, BTW is pretty much 
> down to the tiny 1:20 transformer. I have built variations of this design 
> with bigger transformers that work very well.
>
> There are a lot of variations of power supply design that I could mess 
> with - obviously I have already scoured the internet on this topic - but 
> that is the trouble. This project will never get finished if I have to run 
> through multiple prototypes trying to find one that is small enough and 
> that works. So I was wondering if anyone could just say 'use this design'.
>
> The constraints are:
>
>1. It has to fit on a circular PCB the same diameter as the tube or 
>less (about 17mm).
>2. It has to provide around 150V-160V regulated output, or maybe just 
>'limited' output.
>3. It only has to provide 1.5mA to 2mA.
>4. It has to use a LiPo as the power source, so it should work at 
>voltages between around 3.5V and 4.5V.
>5. It has to use parts I can get from digikey (so no sourcing 
>transformers from old cameras that I can't find for example).
>
> Surface mount components are fine...
>

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Re: [neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Paul Andrews]

Hi David, PM sent...

> On May 2, 2019, at 3:23 PM, David Forbes  wrote:
> 
> I could send you a bunch of the 31105 transformer that I use in my Nixie 
> watch with the LT1308B. 
> They are available from Wurth in large quantity, but no longer a stocked item.
> 
>> On Thu, May 2, 2019, 11:54 AM gregebert  wrote:
>> Sounds like your transformer is saturating; common problem with small 
>> magnetics.
>> 
>> I used an LPR6235-123 from Coilcraft in my wristwatch. They sell to 
>> end-users in small quantities, which is nice.
>> Even though it only ran for 7 seconds at a time, it still overheated at 7mA 
>> load but it's a possible option for you at 2mA.
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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[gregebert]

I meant to say "humiliating"

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[gregebert]

I've done a fair amount of work with flyback converters, or minor variants. 
The other circuit looks like some kind of self-oscillating topology, and I 
have not done anything with those other than build a Radio Shack kit with 
one back in the early 1970's.

I really wish manufacturers would provide decent SPICE models for their 
transformers; I'm cursed with simulating these designs for weeks or months, 
only to find out they behave so much differently on the bench under load. 
It's humbling to experience how a converter works so well with no load, 
only to see it fall to pieces when you put it to work.

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Tomasz Kowalczyk]

W dniu czwartek, 2 maja 2019 20:54:25 UTC+2 użytkownik gregebert napisał:
>
> Sounds like your transformer is saturating; common problem with small 
> magnetics.
>
> I used an LPR6235-123 from Coilcraft in my wristwatch. They sell to 
> end-users in small quantities, which is nice.
> Even though it only ran for 7 seconds at a time, it still overheated at 
> 7mA load but it's a possible option for you at 2mA.
>

Hmm, datasheet of this transformer shows a pretty funky step up circuit. 
Does anyone have a link to description of this circuit, or just name of it?
https://www.coilcraft.com/pdfs/lpr6235.pdf


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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[Paul Andrews]

FYI: This was 
the transformer I was using. The saturation current is 0.7A.

On Thursday, May 2, 2019 at 2:54:25 PM UTC-4, gregebert wrote:
>
> Sounds like your transformer is saturating; common problem with small 
> magnetics.
>
> I used an LPR6235-123 from Coilcraft in my wristwatch. They sell to 
> end-users in small quantities, which is nice.
> Even though it only ran for 7 seconds at a time, it still overheated at 
> 7mA load but it's a possible option for you at 2mA.
>

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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[SWISSNIXIE - Jonathan F.]

One Idea whould be trying to use the LT8580, there is an appnote about 
using it as a VFD Tube supply. Sure, you would need a second dcdc to reach 
9V, but those are super tiny nowadays. Could possibly fit on a 17mm board

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Re: [neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[David Forbes]

I could send you a bunch of the 31105 transformer that I use in my Nixie
watch with the LT1308B.
They are available from Wurth in large quantity, but no longer a stocked
item.

On Thu, May 2, 2019, 11:54 AM gregebert  wrote:

> Sounds like your transformer is saturating; common problem with small
> magnetics.
>
> I used an LPR6235-123 from Coilcraft in my wristwatch. They sell to
> end-users in small quantities, which is nice.
> Even though it only ran for 7 seconds at a time, it still overheated at
> 7mA load but it's a possible option for you at 2mA.
>
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[neonixie-l] Re: Suggestions for a LiPo powered nixie power supply design?

[gregebert]

Sounds like your transformer is saturating; common problem with small 
magnetics.

I used an LPR6235-123 from Coilcraft in my wristwatch. They sell to 
end-users in small quantities, which is nice.
Even though it only ran for 7 seconds at a time, it still overheated at 7mA 
load but it's a possible option for you at 2mA.

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