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Inverter Output Transformer Saturation

Discussion in 'General Electronics Discussion' started by franticEP, Apr 1, 2017.

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  1. franticEP

    franticEP

    4
    0
    Apr 15, 2015
    Hi,
    i'm testing an inverter with these features:
    Fswitching=220KHz
    Fout=3KHz-10Khz
    Vout=150Vac
    Pout=150W
    Current feedback.
    Sinusoidal output is obtained with transformer leakage inductor+output capacitor.
    In the figure below there is the schematic.

    cfcd.png

    The problem is that a little DC component (about 100mA) put transformer into saturation and the output waveform has a distorsion as in figure

    cfcdfo.png

    I don't understand from where it can come this DC component. Could you help me?

    A capacitor could solve my problem? what features should have this capacitor? Ceramic or film cap? I had thought of [email protected] as the voltage across it should never be too high.

    Let me know.
     
  2. duke37

    duke37

    5,298
    739
    Jan 9, 2011
    What has temperature (K) to do with it?
    The H bridge needs two n channel fets and two p channel fets and a level shifter to drive the p channel fets.
    The four transistors will need to be matched to get an average zero transformer current.
    Passing high voltage, high current AC through a low voltage electrolytic capacitor is likely to lead to tears.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If the total time your H bridge remains in one state does not equal the total time in the other state over some large number of cycles, then there will be a net DC voltage across the transformer and a net DC current.

    Yes, a cap would improve things, but the voltage rating would be significantly larger than you imagine.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Not the dreaded KelvinHertz!
     
  5. franticEP

    franticEP

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    0
    Apr 15, 2015
    Why? Could you explain me better?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It's quite possible for it to have -70V on one side and +70 on the other.
     
  7. franticEP

    franticEP

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    0
    Apr 15, 2015
    In case of failure i'm thinkin of protecting device with transzorb across capacitor
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You should possibly study the voltages in series resonant circuits.

    You may want to stay away from resonance, but even still, there will be effects.
     
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