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

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by fireant007, Mar 18, 2016.

  1. spec

    spec Well-Known Member Most Helpful Member

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    UPDATE: 04 of 2016_04_10 THIS SCHEMATIC IS NOW REPLACED BY ISSUE 2 SHOWN IN POST 155

    2016_03_19_Iss01_00_Sh00_ETO_COLD_CATHODE_DISPLAY_TUBEPSU_VER1.png
    ERRATA
    (1) Add a 100nf min 400V min ceramic capacitor across the 183V supply rail for every five cold cathode indicator tubes
    (2) C2 and C8 should be 3300uF (3m3F) for the full complement of 100 tubes. C2 and C8 can be scaled according to the number of tubes used but the minimum value is 100uF.
    (3) The specified transformer has 55V secondary windings not 50V as indicated on the schematic.
    (4) As a result of (3) above the 183V line will be 231V off load.
    (5) The transformer is changed to type MCTA 120/55 (also shown on the data sheet below)


    NOTES
    (1) The circuit can be simplified if a 120WH minimum transformer with a 150V RMS secondary can be located.
    (2) IN-9 cold cathode display tube salient characteristics:
    (2.1) ionizing voltage: 70V
    (2.2) striking voltage: 140V
    (2.3) maximum current: 12 mA
    (3) All capacitor values can be increased provided the type is maintained.
    (4) capacitors can be connected in parallel to make up a value but capacitors should not be connected in series.
    (5) The 183V supply is isolated from the mains supply.
    (6) With 1.2A current drain (100* 12 mA) there will be around 14V peak to peak ripple on the 183V supply line.
    (7) for optimum light control, transistors VT1 to Vt100 should be configured as linear current sinks.
    (8) The IN-9s will be dissipating around 840mW so they should be in a position where air can flow freely around them.

    LINKS
    (1) Mains Transformer
    http://cpc.farnell.com/multicomp/mcta225-55/transformer-225va-2x-55v/dp/FF01588
     
    Last edited: Apr 10, 2016
  2. fireant007

    fireant007 Member

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    Yes .. I think you are correct Les.
    I have been in the shed all day testing again.
    Voltage at the anode is not that important.
    Thanks for taking your meter apart !... must have brought back memories !
     
  3. fireant007

    fireant007 Member

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    I like it Spec... !

    I have seen similar and discounted them (coz I thought I needed constant voltage on the anode) .. but I think it's going to be the best way.
    Would love to keep a transformer out of it.

    Thanks for putting that together... will build and test.

    Cherrs.
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Hi fire,
    You really need isolation from the mains supply for safety reasons and also so that ground currents etc can be isolated from your control electronics.

    I did look at ways of eliminating the mains transformer.
    (1) Use an off line switch mode power supply. For a production design this would be the way to go.
    (2) power directly from the mains supply and use linear opto couplers but this would be complex and expensive in view of the number of display tubes you are catering for.

    A current drive for the display tubes is really the only way, because to a first order approximation, the voltage across the tubes is pretty much constant. If you like I will post an addition to the circuit to give a linear and accurate input voltage to current function which would be muck easier to drive than the present VT base. This would require a cheap quad opamp (£0.33 UK) for each group of four tube current drive circuits.

    spec
     
    Last edited: Mar 20, 2016
  6. fireant007

    fireant007 Member

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    It is going to be double insulated rated. So safety is not an issue.
    However .. you are right .. the ground loops could be an issue !

    The off line SMPS is the way I wanted to go .. but is impossible ... only good for supply voltages above 140Vac.
    Opto couplers intrigues me ?

    I was going to go down the op amp road .. one of the pdf's I posted used them !
     
  7. Les Jones

    Les Jones Well-Known Member

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    One rather daft way that MIGHT work is to start with an old PC power supply and the transformer from another one. Connect the winding that originally rectified to provide the 5 volts output to the same winding on the supply that is still in one piece. Do NOT remove the original connections in the power sulpply that go to the rectifier etc. This is so you still have the feedback loop intact. Connect a bridge rectifier made from high voltage high frequency diodes to the winding that was originally the primary of the spare transformer. This will probably give about 250 volts so you may have to remove some turns from the spare transformer secondry. (Which was originally it's primary.) It may also be possible to modify the power supply to change the voltage at which it tries to regulate the 5 volt output. This would also adjust the high voltage output from the spare transformer.

    Les.
     
  8. fireant007

    fireant007 Member

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    Not as daft as you think Les...
    Already thought off :)

    This what you are thinking of ?

    nix_psu1.jpg

    I have been on this for a few weeks now ! :arghh:
     
  9. Les Jones

    Les Jones Well-Known Member

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    More or less. The 5 volt rail provides the most power. I have just had a look at a spare one and it is rated at 5 V 22 amps (110 watts) and 12 v at 6 amps (72 Watts.) The transformers do not have two 115 volt windings as they are not connected to the AC input. The primary is fed with a pulse width modulated rectangular waveform. This is generated by chopping the 320 volts DC from the rectified mains input. The PWM waveform is at a frequency in the tens or hundreds of KHZ. (Hence the small transformers handling so much power.) 1N4007 diodes will not be suitable to rectify these high frequencies.

    Les.
     
  10. fireant007

    fireant007 Member

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  11. spec

    spec Well-Known Member Most Helpful Member

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    Last edited: Mar 20, 2016
  12. Pommie

    Pommie Well-Known Member Most Helpful Member

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    • Like Like x 1
  13. spec

    spec Well-Known Member Most Helpful Member

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  14. spec

    spec Well-Known Member Most Helpful Member

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    Hi fire,

    Just an observation, the 1N400x diodes are not really designed for high frequency rectification work. You would get much better rectification with a high speed rectifier diodes.

    spec
     
    Last edited: Mar 20, 2016
  15. spec

    spec Well-Known Member Most Helpful Member

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    Hi again fire,

    here is a transformerless CC display PSU which can be switched for 110V and 240V mains supplies. It is non isolated so the control signals for the tube current driver transistors would need to be isolated or the whole system referenced to the voltage rails.
    For 110 V operation only, the two BJTs and eight MOSFETs would not be required.

    spec

    2016_03_20_Iss01_00_ETO_COLD_CATHODE_DISPLAY_TUBE_PSU_VER2.png
    ERRATA
    (1) R8 should be 4K7 not 22R
    (2) For every 10 of CC display tubes (CCDTs) add another 100uF capacitor across the CCDT supply line, in parallel with C3 and C4 as appropriate.

    NOTES
     
    Last edited: Mar 20, 2016
  16. fireant007

    fireant007 Member

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    Holy handgrenade batman.
    You are gold.
    Loving your work Spec.

    Might be a bit of over kill though. Perhaps a transformer after all.
    Particularly as I will have isolation problems and extra switches etc ....


    You are right of course about the in4001's ... just wanted to show that I had been thunking. looking etc

    MCU PWM for nixie's are all the rage btw.

    See attached
     

    Attached Files:

    Last edited: Mar 20, 2016
  17. spec

    spec Well-Known Member Most Helpful Member

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    Glad you liked the circuit.

    I have been having a few thoughts about the control side. One way would be to have a serial data link to control the cc tubes. That way only a single opto coupler would be required to provide isolation in the serial data line.

    But as you say, a mains transformer would be simpler and more efficient. You could probably use a lower VA mains transformer than shown on my schematic in practice too.

    spec
     
    Last edited: Mar 20, 2016
  18. fireant007

    fireant007 Member

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    Here are a few circuits I have collected so far....

    The voltage for the IN-9 is only 125V though ?

    Schematic.gif

    And I found this one particularly interesting ....
     

    Attached Files:

  19. fireant007

    fireant007 Member

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    I like the above circuit.
    This is more in line with my idea of driving with OpAmp's.

    This way I can apply the ideas in this sheet about offsets to zeroing the tube etc.

    Edit: this pdf also drives with PWM in figure 2 ....

    Trouble is the arduino's don't have enough PWM outputs.
     

    Attached Files:

  20. spec

    spec Well-Known Member Most Helpful Member

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    The first circuit looks complicated- not sure what is going on there.

    Although the data sheet shows 140V as the minimum worst case striking voltage most samples of the 1N-9 would strike much lower. The striking voltage is highly dependent of temperature too.

    The second circuit, as you say is interesting, and shows the lengths that designers went to to implement a bit of logic before diodes, then transistors, then logic gates, then micros became freely available and cheap.
     
    Last edited: Mar 20, 2016
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  21. fireant007

    fireant007 Member

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    [QUOTE="The striking voltage is highly dependent of temperature too..[/QUOTE]

    Really ? .. why ?

    Another unknown fact is that any nixie requires a tiny bit of stray radiation (light, cosmic rays, etc.) to pre-ionize the neon gas, and strike.
    I have noticed that a lot of tubes won't light straight away out of the box.
     

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