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555 question

Discussion in 'General Electronics Chat' started by tibbles, Oct 6, 2009.

  1. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    hi all
    something thats always puzzled me, why does the 555 trigger on a negative going signal rather than the more logical, to me anyway, a positive going one.

    i know its easy to work round,
    thank you
    dougal
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,444
    1,075
    Because when you use it as an oscillator, it uses the dropping voltage during the discharge of its RC network to trigger itself.
     
  3. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    thanks mike
    i knew there would be reason

    i suppose before it was used for anything and everything it is an oscillator.
     
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