555 timer 'RC' question

Discussion in 'General Electronics Chat' started by paul19811891, Apr 24, 2008.

  1. paul19811891

    Thread Starter New Member

    Apr 24, 2008
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    Hi
    Just a quick question - Why is it that when you trigger a 555 timer the output goes high immediatley for a set period of time as determioned by the RC network?
    Thanks.
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  3. paul19811891

    Thread Starter New Member

    Apr 24, 2008
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    Thanks, Ill check them out, do you know if Id be right in saying that the reason the output state changes once triggered is because the capacitor is discharging through the resistor for a period of time?
     
  4. sndpgr

    Member

    Jun 22, 2006
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    Are you using the 555 in an monostable mode? if you could provide us with the circuit.. that would be great
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Because when you trigger the 555 it sets its output high and waits for the voltage across the capacitor to be the 2/3 of the supply voltage. It knows when the capacitor attains this voltage by using an internal comparator to monitor the voltage across the capacitor compared to the 2/3 of Vcc. When the capacitor reaches this voltage the 555 resets its output to a low state (it was high).
     
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