Polarity switching and amplification of square wave?

Discussion in 'General Electronics Chat' started by electronice123, Feb 19, 2009.

  1. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
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    I need to build a circuit which does the following:

    20kHz square wave amplified to high voltage with a transformer which has both a positive and negative output. I need the outputs to switch polarity every pulse.

    How can this be done?
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    A step up transformer with a center tap can do that, if it's carefully terminated.


    eric
     
  3. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
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    Can you explain in detail how that works?
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    You can generally pass a square wave through a transformer if you avoid any self-resonant frequencies, and it's got enough bandwidth to pass at least the fifth harmonic. For example, at 20 KHz, you want a transformer that's flat up to around 100KHz. Most of your high quality switching power supply transformers can do that. You need to put a matched load resistance on it, however, or it may "ring" which may or may not be a problem. How critical is it to have a very sharp square wave on the output?

    eric
     
  5. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
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    From what I can tell it's not critical.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    For what do you need the high voltage ?
    How high is your high voltage ?

    Greetings,
    Bertus
     
  7. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
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    The high voltage will be used to charge a capacitor with a polar liquid dielectric. It has been said that the liquid dielectric can be heated, I'm doing it for a science experiment but I don't think it will work.
    500V-1000V will be plenty
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    How many current will flow in the dielectric ?

    You could use a inverter like schematic with a CT transformer like eric siad.
    Here are some schematics used for fluorescent lamps.
    http://ludens.cl/Electron/Fluolamp/fluolamp.html
    The last one is designed for ca. 25 khz.
    (You can drive the transistors with a controlled oscillator in stead of selfoscillating).

    Greetings,
    Bertus
     
  9. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
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    I think the secondary will be less than 100mA.
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    So you end up with 50 to 100 Watts.
    Then the proposed schematics I shown you are to small.

    Perhaps you can scale it up.

    Greetings,
    Bertus
     
  11. electronice123

    Thread Starter Senior Member

    Oct 10, 2008
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    0
    I'll keep working and researching and see what I can figure out!
     
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