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  1. #21
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    Re: UC3845 ETD29 transformer PWM signal

    Faulty scope probes or "open ckt" gnd connections will not help in fault finding, hopefully your fet and driver and associated cktry have survived and you can check the transformer phasing

    you can also run the ckt off a say, 24V, DC supply with a 1A current limit, and a 12V supply for the chip - this will allow you to play around and not damage things if you slip with a probe, or the Tx is horribly wrong ...

    best of luck ...



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  2. #22
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    Re: UC3845 ETD29 transformer PWM signal

    I have some progress in design by taking your help.
    Supplying IC and feedback side from exteranl source circuit seems to ok. As you can see photo my drain signal without loading. Although I did not make any calculation for clamp circuit, ıt seems to ok. But there is some ringing. I realize that changing mosfet, ringing change. I think, because of drain-source capactiance and leakage inductance cause some ringing. And the speed of turn of. V=L.di/dt

    1. Clamping is ok?
    2. My next step, I will do it, without external suppy.(If aux winding is ok, it must be start around 8.65V). And what is the suggestion to test before loading ?
    3. Also, I work on slope compensation on feedback loop, there is two books which are Sanjaya Maniktala - Switching Power Supplies A - Z and Christophe Basso - Designing Control Loops for Linear and Switching Power Supplies. I am not sure that I can figure out but I will try.
    Click image for larger version. 

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    Last edited by ivan_mateo; 2nd April 2020 at 07:50.



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  3. #23
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    Re: UC3845 ETD29 transformer PWM signal

    The ringing is normal for light load - the overshoot is not too bad either - try higher loads ....


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  4. #24
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    Re: UC3845 ETD29 transformer PWM signal

    The ringing occurs in discontinuous mode when the rectifier current flow stops. It's a high impedance/low energy oscillation (frequency set by main inductance and sum of winding, transistor and rectifier capacitances), usually not critical regarding EMI.


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