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stepdown switchers

Discussion in 'Electronic Design' started by Jamie Morken, Jan 8, 2004.

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  1. Jamie Morken

    Jamie Morken Guest

    Hi all,

    I have noticed the following about step down switchers using national.com
    "webench" tool for the LM2675-ADJ 1Amp/260kHz stepdown switcher with 12V
    output:

    1. input voltage up, output coil uH up
    2. output current down, output coil uH up (to rated current of switcher chip
    anyway)
    3. output voltage down, output coil uH down

    Are these observations always applicable to stepdown switcher designs?

    Why would the output coil inductance increase if the current draw decreases?
    Is it ok to design the step down circuitry to handle 1Amp even if at times
    there will be only 100mA current draw? Will the 12V output remain stable in
    this case? The input voltage is between 24V and 36V.

    cheers,
    Jamie Morken
     
  2. Mac

    Mac Guest

    Doesn't the webbench design tool prompt you for a minimum current?

    In general I don't think there is a single answer. It seems like the
    mimimum current would depend on the minimum duty cycle. For a pure
    hysteretic converter there is no minimum current.

    Mac
     
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