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SMPS power supply help needed

Discussion in 'Electronic Design' started by rob, Feb 6, 2004.

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  1. rob

    rob Guest

    Hi to all.
    I am building a 12 to 19V @4A convertor using an uc3843 controller
    chip.
    I am using an inductor , not a xfmr , so there is no isolation. The
    frequency
    is 300khz.
    I was wondering how to calculate the compensation components , in and
    around the feedback cct.Looking on the internet at various ccts using
    this chip
    I have seen wildly differing values. The resistor / cap combination
    from the output of the error amp to the - input is 100k // 100p at the
    moment. I have seen values from 220k// 100n . (yes , that is nano)
    At the moment the convertor is "working" , but it is making a high
    frequency
    singing / hissing noise , which it should not do.
    Any help would be appreciated.
    Cheers
    Rob
     
  2. So a Buck converter?
    Three ways to go:

    1. Go to the library and get a book on SMPS design - read your way through
    it a do the math

    2. Fiddle your way through the design by measuring the gain/phase response
    at all possible load and input voltage situations. The select the
    compensation circuit to get 60 degree phase margin and 10dB gain margin

    3. Write down the equations for the power stage, PWM modulator and error
    amp. And then workout the feedback components accroding to the 60degree/10dB
    rule

    Cheers

    Klaus
     
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