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WEBENCH® Tools/LM5023: Universal Input to 90V@5W isolated converter design

Suyon
Prodigy 120 points
Part Number: LM5023

Tool/software: WEBENCH® Design Tools

Hi.

I need to design a universal input to 90V@5W isolated converter.

This converter must have a very low output voltage ripple, typically lower than 50mV and high efficiency higher than 85%.

It seems to be good to use LM5023 with flyback topology.

But in order to keep the converter in continuous current mode for lowering the output ripple , the inductance of transformers will be high and so transformer big.

And the maximum switching frequency of LM5023 is 130kHz, not so high.

Please help me how can I realize this converter optimally.

Thanks! 

  • 0
    Prodigy 120 points

    And the Quasi-Resonant Operating of LM5023 is based on discontinuous current mode. 

    So I worried how I can satisfy the output ripple requirement in discontinuous mode.

  • 0 in reply to Suyon
    TI__Guru 74985 points

    Hello Suyon,

    For these low power applications +/-10% ripple is generally acceptable which would be 100 mV for a 5 V application.  However, if you would like the ripple to be less than 50mV just requires selecting and output capacitor with ESR that can support it.

    ESR = Vripple/Ipeak

    Another thing that may help is a PI filter.  Just separate your output capacitors with a chip inductor.

    Please also note we also have 5W off line reference designs and EVM that you might find useful.  You enter your input and output requirements and a list of designs will come up that already meet this requirements.  The following link will get you these to reference designs.

    Regards and thankyou for choosing TI for your next power supply design.

  • 0 in reply to Mike O'
    Prodigy 120 points

    Thanks, Mike.

    What you mean is if the output ripple requirement would not be met, I can add an another output filter network such as PI filter, right?

    I think it's nice idea.

    I will send you the shcematic of my design. 

    If do not mind, look at that and say if any problem.

    Thanks a lot.

    Sorry, I do not know how to upload my file and send you.

  • 0 in reply to Suyon
    TI__Guru 74985 points

    Hello,

    To answer you question.  Yes you can use a PI filter if you have trouble meeting the ripple specification.  However, selecting the capacitor with correct ESR value is the secret to hitting your goal

    We can give your schematic a review if you send it.

    Regards,