555 timer implement

Discussion in 'General Electronics Chat' started by bowen, Jan 15, 2008.

  1. bowen

    Thread Starter New Member

    Jan 15, 2008
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    how to derive the formula for 555 timer which is built by using one SR-FF 2 opertional amplifer and 1 bjt 4 resistor (3 5k and one unknown) with vcc =5v
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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  3. thingmaker3

    Retired Moderator

    May 16, 2005
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    I don't think a 555 equivalent can be made with only one op-amp. A comparator is needed for both threshold and trigger inputs.
     
  4. algae

    New Member

    Jan 14, 2008
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    Didn't I read somewhere that you can make a comparator out of an op amp with a simple mod...or am I just smoking something?
     
  5. FredM

    Senior Member

    Dec 27, 2005
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    Its not good practice, but you can use op-amps as comparators. No mod is required, but you need to check specification against application - primary areas being voltage ranges for inputs, and differential input voltage.. Also, stability can be a problem with open-loop operation of an opamp.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Stability (if you're talking about possible oscillation) isn't a problem. Slew rate is a problem.
     
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