Dummies guide to building a 120watt 140 volt power supply to drive IN-9 Nixie tubes.

[fireant007]

I am preaching to the wise again.
I do know the various flavors of C, but focus on C# mostly now and some time will find out what Python is all about.
I also read all the books about Object Oriented Software as you seem to have done.
My experience with software/hardware systems is that the two development teams never communicate well, and you find the softies going through all sorts of antics to match a particular hardware interface when the hardies could reduce much of the code with a simple hardware redesign here and there. And the converse is also true.

Yeah, I would love to do some microcontroller experiments... its the time though.
spec

Lucky I am stupid enough to try to do it all myself !!!!

 

[spec]

Lucky I am stupid enough to try to do it all myself !!!!

That should result in the optimum system then.

 

[fireant007]

Still have to get a power supply first !
Rigol should help .. as I am flying blind here.

 

[spec]

Still have to get a power supply first !
Rigol should help .. as I am flying blind here.

I wouldn't worry about the PSU- that is the easy bit. The control will be the critical area and the physical build with one hundred tubes.

 

[fireant007]

Am I on the right track to desexing my supply ... ie: with the rails etc ?

 

[spec]

Am I on the right track to desexing my supply ... ie: with the rails etc ?

Yes. I will post a single sex circuit.
spec

 

[spec]

About the transformer.

You may be able to get away with a Multicomp MCTA120/55
Diameter: 95mm
Height: 47mm
Weight: 1.32 Kg
https://cpc.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15002&langId=69&storeId=10180&categoryName=All Categories&selectedCategoryId=&gs=true&st=transformer 55V
https://www.farnell.com/datasheets/1945759.pdf

Les suggested this way back in post #13

 

[fireant007]

Whoops... looked at the wrong one.
Yes .. not 2.5 kgs. only 1.32 kg as you say.

The original post title don't tell no lies .. this is the dummies guide !

Well since that is so small... cough.
I guess that would be a better option as I would not need a whacking great heat sink ?
And all my isolation problems also vanish !

 

[spec]

Here is a unisex NMOSFET version of the PSU.
I have also reduced the number of MOSFETS from eight to six which should be OK.

 

[spec]

Whoops... looked at the wrong one.
Yes .. not 2.5 kgs. only 1.32 kg as you say.

The original post title don't tell no lies .. this is the dummies guide !

Well since that is so small... cough.
I guess that would be a better option as I would not need a whacking great heat sink ?
And all my isolation problems also vanish !

No you were right. The transformer I specified did weigh 2.5Kg. I suggested to try using the transformer that Les suggested initially, which is much lighter. I feel a bit more confident about this change because I now understand the operation of the tubes a bit more and also have more information about your application.

I think the mains transformer approach is the best all round. If you could get a transformer with a single 150V secondary winding that would be ideal.

spec

 

[fireant007]

Q11 makes all the difference !
Can't wait to look what is going on with this wif me new scope !
Thanks a bunch Spec.

Will build both versions (transformer too) and see how they compare.
Just guessing but I think you have the 115/240 volt switch arse about ?
Arn't the outside rails 240vac from the bridge ?

 

[fireant007]

Ahh.... so I am not going mad.

Gotta sleep here .. it's 9:30 PM !

Ordering trannie tomorrow...
Might see if a local manufacturer can make me one at a reasonable cost.
Night Night

 

[spec]

Q11 makes all the difference !
Can't wait to look what is going on with this wif me new scope !
Thanks a bunch Spec.

Will build both versions (transformer too) and see how they compare.
Just guessing but I think you have the 115/240 volt switch arse about ?
Arn't the outside rails 240vac from the bridge ?

No sweat fire,

No, the 110V AC and 240V AC selector is correct (as far as I can tell). On 110V input there will be around 153V between the supply rails and with a 240V input there will be 339V between the supply rails. The idea is that with the 153V supply rail, the 100 of tube circuits are all connected across the supply rails. With the 339V supply rails the MOSFETS & co divide the 339V supply in half to produce two 169.5V supplies. The upper bank of 50 tubes is connected to the upper supply and the lower bank of 50 tubes is connected to the lower supply.

spec

 

[spec]

Here is a simpler version of the non transformer, non isolated cold cathode indicator tube tube PSU.
Rather than dissipating the power in an array of MOSFETs, the power is dissipated in two high power resistors which can operate at a much higher temperature than semiconductors and thus will be adequately cooled by a smaller heat sink.
The two power NBJTs dissipate 23W worst case so they will also need a heat sink which they can share as only one of the NBJTs will be dissipating power at any one time. This is also the case for the power resistors, which are the bolt-down type as shown in the data sheet links.

​

ERRATA
(1) Increase C1 to 220uF 400V or larger.
(2) Fit 100uF 250V capacitor across the respective tube supply rails for every 25 tubes
(3) C4 should read 100uF 250V not 400V
(4) Fit 1N4148 diode anode to Q6 emitter and cathode to D7 anode (upper). This is for reverses VBE protection on mains power switch off.
(5) Fit 1N4148 diode cathode to Q6 emitter and anode to D3 cathode (lower). This is for reverse VBE protection on mains power switch off.

NOTES
(1) with a 240V mains input, the voltage across C1 will be 340V peak. The function of the high power transistors, and associated components, is to generate a midpoint in the 340V rail to give two 170V supply rails, one for the upper bank of 50 tubes and a second for the lower bank of 50 tubes.
(2) With a 110V mains input, the voltage across C1 will be 153V peak. This will be the supply rail for all the tubes which will be connected in parallel by the mains selector switch.
(3) For 110V mains supply operation the high power transistors and resistors and associated circuit components are not required.
(3) The high power transistors and resistors will only dissipate worst case power when one bank of 50 tubes is conducting no current and the other bank of 50 tubes is conducting full current (600mA total)
(4) The two 220 Ohm high power resistors dissipate 74W worst case and can be mounted on the same heat sink as only one resistor will be dissipating power at any one time. This heat sink will get very hot under certain circuit conditions and needs good ventilation and safety measures to prevent human contact. Also the resistor heat sink should not be mounted in a position to heat other components and especially should not be able to heat any flammable materiel.
(5) The two high power NBJTs dissipate 23W worst case and should be mounted on a separate heat sink to the power resistors. But similarly, the two high power NBJTs can be mounted on the same heat sink.


DATA SHEETS AND SOURCES/COST
(1) MJW18020
https://www.onsemi.com/pub_link/Collateral/MJW18020-D.PDF
https://uk.rs-online.com/web/p/bipo...D4D4A573138303230267374613D4D4A57313830323026
https://www.digipart.com/part/MJW18020
https://www.mouser.co.uk/Search/ProductDetail.aspx?qs=HVbQlW5zcXX%2bSmQG5przbA==
(2) 2N6517
https://www.onsemi.com/pub_link/Collateral/2N6515-D.PDF
https://uk.rs-online.com/web/c/semi...67573743D324E36353137267374613D324E3635313726
(3) 2N6520
https://www.onsemi.com/pub_link/Collateral/2N6515-D.PDF
https://uk.rs-online.com/web/c/semi...67573743D324E36353230267374613D324E3635323026
(4) Power Resistor
**broken link removed**
https://cpc.farnell.com/1/1/4742-te-connectivity-cgs-hsc100220rj-resistor-ww-100w-5-220r.html

 

[fireant007]

Wow... data sheets too.
I owe you a scrumpy or 3 for this. (somerset's national drink ?)

I "think" I have found a fault in the circuit though.
The 4k7 resistor must be put on the anode .. no the cathode side.

I take it that the 110/240 switch is shown in the 110v position ?

 

[spec]

Wow... data sheets too.
I owe you a scrumpy or 3 for this. (somerset's national drink ?)

Yes, the national drink in Zummerset is scrump or scrumpy jack- sweet and rough. Only men drink rough.
There is also a retail cider called Old Rosie- if you ever visit the West Country in England don't ever drink it.

I "think" I have found a fault in the circuit though.
The 4k7 resistor must be put on the anode .. no the cathode side.

The 4K7 resistors are on the cathode side of the tubes and are in the correct position. They are only there to protect the driver transistors from the blood and thunder going on in the tubes and to provide a degree of protection from ark-over or any other strange effects that you get with valves (tubes). In addition, they lower the dissipation in the driver transistors.

I take it that the 110/240 switch is shown in the 110v position ?

The mains input voltage selector switch is shown on the schematic with its wipers up, which is the 240V mains input position. The labels above and below the switch schematic symbol indicate the position of the switch wiper for the two mains input voltages.

spec

 

[fireant007]

Err.. sorry .. have to disagree.
The anode resister MUST be put before the tube.
I have run tests.
It will light using your circuit but only if you turn the vaiac up to about 300V and then is switches on (all segments lit) and draws god knows how many amps coz it's brighter than the sun !

I have been drinking that exact scrumpy ... it says the use by date is next year some time.
I disagree.
It says its matured in old oak vats..... just how old .. exactly ? ... was Noah building his ark from the same wood ?
Taken me a month to get this far through.

 

[fireant007]

Experimenting with muller and pancake tubes ... think I will just stick with the ST-21 .. not much performance gain really .... not for what I want.

 

[fireant007]

Ok.. have done some measurements

Voltage in across C1 = 156 Vdc (adjusted with vairac)

Voltage across 4k7 resistor 55 Vdc
Watts = 0.66 @ 12mA

Voltage across IN-9 99Vdc Fully lit from end to end. @ 12mA is drawing 11.88W ! ? That can't be right I it's just not that hot ? I could toast bread with 100 of them !

It must be though ... coz 55Vdc + 99Vdc + whatever is across the 220 ohm resistor adds up to 156 Vdc !

Edit: Thanks to Les for pointing out that my maths is wonky .. it is actually 1.188W !

Current across 220 ohm resistor (emitter output) 12 mA (No transistor in circuit)

Nope ... I am going to HAVE to multiplex this.
Good ... news .. I can use a MUCH smaller power supply !

Will still build this one.. and multiplex in software to see what happens !
From what I have read ... multiplexing is fraught with problems like noise etc.

Post from a group I belong too.
https://groups.google.com/forum/#!topic/neonixie-l/gqA6OpDbdXM

 

[spec]

Hi fire,
Not sure where to start.
But can I just say that you are not testing the circuit correctly.
You must have a transistor in the drive circuit or you cannot define the ionizing current and will blast the tubes to hell.
If the position of the 4K7 makes any difference there is something badly wrong somewhere.
Can you check that the circuit is wired as per the schematic?

spec