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  1. #1
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    Smps design with UC3844 for 300V /0.5A

    Hi,

    My smps design design spec is 300V, 0.5A .

    I got design from powersim.com online(online smps design) Attached schematic

    In this Primary MOSFET failing continuously . Not able to get output.

    Help me on this

    Thanks

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  2. #2
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    Re: Smps design with UC3844 for 300V /0.5A

    Although it's feasible to use smps method to convert mains AC (assuming 230V) to 300 VDC...
    I can't help but think there's a simpler topology. It looks as though C6 acquires 330 VDC peak. C6 provides power to your converter.
    (330 is 230 Times Square root of 2, the standard formula for calculating peaks of a sinewave.)

    This is very close to your desired 300V figure. In fact if your house voltage droops to 211 VAC then C6 has 300 VDC. You can feed that directly to your project.



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  3. #3
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    Re: Smps design with UC3844 for 300V /0.5A

    transformer design and phasing of windings is critical to the flyback circuit working - as is making sure the feedback is working before applying serious power ...



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  4. #4
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    Re: Smps design with UC3844 for 300V /0.5A

    R7, at 12k, is way too low ohmic value.
    Please tell what is R7?...what package and power rating?


    Also, what is your Z4 value....you could be overvoltageing your TL431 if its too low

    Also, what is your transformer turns ratio...remember that "V referred to pri " is "vsec * NP/NS"
    Do you know how to work out the polarity of a flyback transformer coils?.....ie, assign a dot to one end of one coil, then go through and measure it connected to another coil...see if inductance is more or less than the coil on its own....bla bla bla etc etc etc...

    Also, are you using a PCB, or is this wired on a breadboard? (hopefully not breadboard and wires)

    - - - Updated - - -

    Also, your D1 is in the wrong place.

    Your sec diode is only 600v rated.....please tell what is your turns ratio.
    You also have no rc snubbing across your output diode.

    - - - Updated - - -

    Also your diode bridge is only 400v rated, and friends tell me that voltage transients in India are way above this.


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    Re: Smps design with UC3844 for 300V /0.5A

    You probably know the next suggestion......get rid of the isolation, implement resistor divider feedback straight to the uc3844, power the uc3844 with an isolated bench psu and remove the bias coil diode.....
    ...get it working like that, or try to, and see where you are.
    No point in doing the whole lot all at once when you are struggling.



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