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  1. #1
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    FAN6754 flyback converter-overcurrent problem

    I have a design 193V output voltage and 700mA current, but when the current drawn from output, the auxilary winding voltage fall down, and IC shut down PWM gate signal as you can see in the attachment and the output voltage go to zero. And I could not understand, why auxilary voltage is like sawtooth wave, I think the IC try to open PWM but can not start. Can any body help me about that issue? ( Yellow is C9 voltage green is C10 and purple voltage is Gate)
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  2. #2
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    Re: FAN6754 flyback converter-overcurrent problem

    Hi,

    Is it a new design, or do you try to repair an old circuit?

    If "repair" ... I assume C9 is dried out and needs to be replaced.

    Klaus
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  3. #3
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    Re: FAN6754 flyback converter-overcurrent problem

    I need to repair, I have one board it is working, but it that I could not find fail. C9 look like new, anyway I can replace it.

    - - - Updated - - -

    Quote Originally Posted by KlausST View Post
    Hi,

    Is it a new design, or do you try to repair an old circuit?

    If "repair" ... I assume C9 is dried out and needs to be replaced.

    Klaus
    I need to repair, I have one board it is working, but it that I could not find fail. C9 look like new, anyway I can replace it.
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    Re: FAN6754 flyback converter-overcurrent problem

    Hi,

    I'm not familiar with the scope you are using.

    Does it show "1s/div" and "2s/div"?
    --> If so, then it's most likely not the C9 problem.

    Klaus
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    Re: FAN6754 flyback converter-overcurrent problem

    Quote Originally Posted by KlausST View Post
    Hi,

    I'm not familiar with the scope you are using.

    Does it show "1s/div" and "2s/div"?
    --> If so, then it's most likely not the C9 problem.

    Klaus
    no, It is 10V, each line mean 2 V.



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  6. #6
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    Re: FAN6754 flyback converter-overcurrent problem

    did you look at it with thermal camera?...see if anything getting hot...there is a good therm cam you can buy for £150...ask me and i will tell you part number.

    otherwise, strip it down and see what you can get working....eg disconnect components and give the FAN6754 a dc bias voltage from external supply then see.
    ....take off output diode....shove vout on it with an ext psu...and see if their is output short circuit...etc etc...

    - - - Updated - - -

    maybe one of the aux caps is dry...replace all.



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