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555 pulse generator

Discussion in 'General Electronics Discussion' started by pwnstars, Nov 10, 2016.

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  1. pwnstars

    pwnstars

    15
    1
    Oct 6, 2015
    Hello there... :)

    Im currently building a pulse generator using 555 timer. The attached photo shows how its setup.
    The frequency changes works just fine BUT the output voltage varies when i change the freqency. When set to low frequence (1-20Hz) i measure 5V peak to peak but when i turn up the frequency it gradually decrease the voltage and ends up with 4.4V at 2k Hz, even without load.

    I guess thats not supposed to happen.
     

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  2. hevans1944

    hevans1944 Hop - AC8NS

    4,534
    2,110
    Jun 21, 2012
    What value of resistance are you using for R2? How much stray capacitance is there from output to common? Can you post oscilloscope photos of the problem? What are you going to use the output pulses for? If you need pulses with 50% duty-cycle, it is better to run the 555 at twice the desired frequency and divide the output with a flip-flop.
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    10,309
    2,238
    Nov 17, 2011
    In addition: which type of 555 do you use? The bipolar or the CMOS type? The bipolar type is not suitable for rai-2-rail output voltages.
     
  4. Chemelec

    Chemelec

    291
    47
    Jul 12, 2016
    How are you Measuring that output Voltage?
    A Multi-Meter is Not very good for LOW Frequency.
    An Oscilloscope would be Best!
     
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