Flyback transformer help

Discussion in 'General Electronics Chat' started by Garurumon, Sep 21, 2013.

  1. Garurumon

    Thread Starter Member

    Mar 17, 2013
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    My question is probably stupid, but heh, I don't know the answer.

    So, I was bored and I wound this little flyback transformer:
    http://www.youtube.com/watch?v=oeP6p3asED0&feature=youtu.be

    Now, I'd like to make it a real "flyback", by adding HV diode and HV capacitor block so I can make a little plasma speaker, but I don't know what side of the secondary should I choose for the diode :D

    1 wire melts, the other one is not melting, which should be connected to the diode?

    This is the configuration:
    http://upload.wikimedia.org/wikiped...entions.svg/250px-Flyback_conventions.svg.png
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would think it would not matter, but if you are referencing the output to a chassis grounded circuit, it might be prudent to use the last conductor off the winding as the common?
    Max.
     
  3. Garurumon

    Thread Starter Member

    Mar 17, 2013
    99
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    The intention is to make a somewhat stable DC output with only 1 cap and 1 diode, but I don't know which wire should I use for diode, and which for the ground.

    I mean, once the mosfet is OFF, when magnetic field collapses, the energy contained in the core should choose the easiest way out, and that is through the diode to the capacitor, but I noticed that wires do not behave the same, and that is what confuses me, do i put it anyway I like it, or should I choose carefully after all?
     
  4. Garurumon

    Thread Starter Member

    Mar 17, 2013
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    And btw, there will be no load, only secondary ends put a centimeter apart so the air is ionized and plasma occurs.
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
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    With a flyback transformer, it matters a lot which way round the diode is - you have a 50% chance of getting it right first time, otherwise you end up with a low voltage forward converter that needs a diode with a huge PIV.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    If all you want to do is draw a spark - the diode is irrelevant (unless you put it the wrong way round).
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Method of determination?
    Max.
     
  8. Garurumon

    Thread Starter Member

    Mar 17, 2013
    99
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    Okay, so it's time for my paint skills. I attached a picture. Now, knowing the winding directions and how the voltage is applied, which of the following two should be done?
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Right side drawing of post #8 matches the phasing shown in post #1.

    You can think of the phasing dot as the wire going a certain way around the core, and as long as you are consistent you are free to make that any choice you want.
     
  10. Garurumon

    Thread Starter Member

    Mar 17, 2013
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    Phasing = in which direction coils induces magnetic field into the core?
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    If you intend to create an arc, you don't want to rectify/smooth it. The internal impedance of the secondary and the breakdown potential of the gap will create a relaxation oscillator that discharges the capacitor at a slower rate than your converter switching frequency.
     
  12. Garurumon

    Thread Starter Member

    Mar 17, 2013
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    But will the rectified arc be bigger?

    I've done it before with DC flybacks and it was pretty cool.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    From around 15 - 20kHz onwards, you can generate pretty impressive arcs with surprisingly low (ish) voltages.

    If the air between the electrodes is still ionised from the last spark, it doesn't need much for the next one to make it across.

    BTW: what exactly is a "DC flyback"?!

    A loose 24kV EHT lead in a CTV is theoretically DC because of the capacitors in the diode-split voltage multiplier, the 'capacitors' are actually the interlayer capacitance of successive layers of windings - so you could say it has a bit of ripple.

    The loose EHT lead will draw a very long "whistling" arc - when connected to the large capacitance formed by the inner & outer conductive coatings of the CRT flare, that capacitance charges up via the relatively large internal resistance of the EHT transformer - if it has an (unintended) spark gap; it will crack over at much lower frequency than the horizontal frequency.
     
  14. Garurumon

    Thread Starter Member

    Mar 17, 2013
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    By DC flyback I mean the real flyback topology, such as ones inside the CRT's, with inbuilt diodes and capacitors.

    My transformer has nothing on the secondary side.
     
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