Buck Converter inductor sizing question

Discussion in 'Homework Help' started by notoriusjt2, Oct 18, 2010.

  1. notoriusjt2

    Thread Starter Member

    Feb 4, 2010
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    [​IMG]
    my work
    [​IMG]
    through trial and error I chose 22.5microH to work with

    D=duty ratio is the fraction of the switching period that the switch is closed

    I think this statement may be throwing me off
    "Determine the size of the inductor such that the minimum inductor current is 25% of the average inductor current."

    so does that mean that if the average inductor current is 1.25A then the minimum inductor current has to be 25% of that? or .3125A

    I have tried all these values of inductors and none of them result in that answer
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    You have the mean current of 1.25A.

    The minimum ripple value is to be 25% of that or 0.3125A.

    The difference between 1.25A and 0.3125A is 0.9375A.

    The peak-to-peak ripple current is then 2*0.9375 = 1.875A

    ΔIl=1.875={[Vs-Vo]/L}*DT

    DT=0.6666/40000=16.67 us

    L= [Vs-Vo]*DT/ΔIl=[30-20]*16.67/1.875 uH = 88.9 uH
     
  3. notoriusjt2

    Thread Starter Member

    Feb 4, 2010
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    so\DeltaIl is the peak to peak ripple current??

    in my textbook it defines it as the "change in current"
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Yes - my wording is intended to imply the same thing.

    BTW - Why did you delete the other post - it might have been of interest to others?
     
    Last edited: Oct 18, 2010
  5. notoriusjt2

    Thread Starter Member

    Feb 4, 2010
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    I didn't delete it... It just disappeared. I still need to work out that problem so I guess I'll repost it. Could a mod have deleted it?
     
  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    That's strange. There was nothing I recollect in the content that would make it a target for deletion - even something as trivial as duplication of an existing thread. Might be worth informing the administrator.
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I made a remark on the missing posts to the other forum leaders.

    Bertus
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    Sorry notoriusjt2,

    Mia culpa.

    I think I deleted the thread since it appeared to be an accidental double post.

    Can you repost the question?

    hgmjr
     
  9. notoriusjt2

    Thread Starter Member

    Feb 4, 2010
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    no worries
     
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