Poorman’s Buck Schematic Doubt.....?

Discussion in 'The Projects Forum' started by corefinder, Oct 25, 2012.

  1. corefinder

    Thread Starter Member

    Oct 6, 2011
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    I have one doubt in this schematic. It has one diode D1. Why it is there won’t it will get short and all the current will drain through it.I have attached the schematic.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    What do you mean "it will get short"? Why would it? It's a flyback diode for the inductor current.
     
  3. corefinder

    Thread Starter Member

    Oct 6, 2011
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    Its diode D1 I am talking about. Its D3 diode that will work as flyback diode.
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have taken the schematic from the PDF, so others can view it directly.

    [​IMG]

    The D1 diode is for the reference voltage for the current setting.

    Bertus
     
  5. corefinder

    Thread Starter Member

    Oct 6, 2011
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    Ok I got it.Thanks Bertus.
     
  6. DickCappels

    Moderator

    Aug 21, 2008
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    So the answer to the original post, based on Bertus' reply is "Yes, is has current going to ground; that's the way its supposed to work."

    My question (not intending to hijack) is whether the 2 mv/°C drift is compensated for somewhere.
     
  7. Mustafatarhan49

    Member

    Aug 16, 2012
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    What about D2? Why is this D2 used in reverse polarity ?
     
  8. t06afre

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  9. t06afre

    AAC Fanatic!

    May 11, 2009
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    The circuit comes from this site ttp://www.instructables.com/id/Poormans-Buck/
    R1 will limit the current through D1 to a safe value for the diode. Without R1, D1 would have been acted as short. And very quickly gone up in flames
     
  10. Sensacell

    Well-Known Member

    Jun 19, 2012
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    D1 is acting as a crude voltage reference ~ 600 mv forward conduction voltage.
     
  11. Mustafatarhan49

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    Aug 16, 2012
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  12. t06afre

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    Because the LM393 has what is named a open collector output http://en.wikipedia.org/wiki/Open_collector
     
  13. Mustafatarhan49

    Member

    Aug 16, 2012
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    Ahan yeah I see that! THanks a lot!
     
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