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Thread: vacuum tube smsp

  1. #21
    .... Silvio's Avatar
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    Have you tried winding the 64 turn in bifilar fashion? Are you using a layer of tape between each winding. Are you leaving 4mm margin space at the bobbin cheeks? I think your winding is arching and shorting out due to the high voltage.

    Are you using a snubber in the primary? any spikes in the primary will be amplified in the secondary winding and the voltage here may rise more than a 1000v. If your insulation is not correct the secondary winding may arc and short out.

    When trying out the transformer put a small load on the output. This will help control any excess voltage spikes generating very high voltages. Try to never start the transformer with the secondary high voltage open.

    Lastly use new enameled copper wire. see that it is in good condition. Use mylar tape for insulation and not something else.

    Good luck

  2. #22
    I did not know if I needed to put a small load on the high voltage secondary test.
    I would like to adjust one more output voltage.
    We expected the output voltage to change when the input voltage of PWM changed, but it did not change much
    I want to know how to change the secondary voltage.

  3. #23
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    If you are opting for regulation keep in mind that this is done in the primary winding. If you have more than one secondary than all the secondary voltages vary together. Having such a high output voltage it would be some what difficult in a way to control from the high to the low voltage as the margin of error will be quite large due to that the control voltage will be more or less 2.5v and the output being around 400v.

    I guess you have to choose another winding with a lower voltage to do this. You will have to use an output inductor with the winding that is being sensed. This is important otherwise it will not regulate properly. You must also have a minimum load with the output when using regulation.

    If you are expecting the output to change you must load it a little so that the excess charge on the capacitors will fall down accordingly. If you are still getting a higher voltage than needed than you have to adjust the winding turns. You can use the formula

    155v / primary turns = volt per turn. Here you will be close to the wanted voltage.

    Regards

  4. #24
    I am trying to adjust the secondary voltage.
    Even in normal smps, there is VR for fine tuning
    Try to vary the voltage by about 10 to 20%

  5. #25
    This is an OTL tube amp.
    The secondary voltage is 150V, -150V.
    Change this voltage.
    Adjusting the voltage of the sg3525 no1 pin changes the PWM pulse width.

    When the pulse width changes, the voltage must also change accordingly, but it does not change much.
    I want to know how the voltage is controlled.

    OTL-1.jpgOTL-2.jpgOTL-전원부.jpg

  6. #26
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    I can see you make a nice job there. I would rather see some oscilloscope shots showing how the pulse width is changing.
    The voltage is controlled by changing the pulse width. However the output must be loaded to see the voltage change. A narrow pulse will give a low voltage and a wider pulse will give higher voltage.

    We like to see a schematic of your setup to see what you actually did. You can draw it up by hand and take a photo of it.

  7. #27
    GATE Pulse PWM control by varying width
    The output voltage is almost unchanged.

    Yellow is GATE PULSE
    Light blue is output
    Attached Files Attached Files

  8. #28
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    Do you have a load on the output? Without it the output voltage never changes.

  9. #29
    connect Load does not change the voltage

    The voltage changes only when the waveform begins to distort
    Attached Files Attached Files
    Last edited by eonscom; 05-30-2019 at 03:03 PM.

  10. #30
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    The output voltage will change with a narrow pulse width if it is loaded enough. It seems that the output is still holding the peak voltage by the output capacitor. Remember that every time the transistors switch the primary winding it is always the full voltage. If the output is loaded correctly then the voltage should get lower with a narrow pulse. I hope your feedback is sensing the voltage you are measuring.

    One other option for you is to increase the inductance of the output inductor if the load is very small. You can also reduce the value of the output capacitor.

    PS We never saw your schematic diagram please post it if you want help as I am blind folded what you actually did.

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