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    Oscillator not oscillatiing

    Designed to: 3.9Hz 50% duty 10v astable.

    CircuitClick image for larger version. 

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    Cannot figure this, the specification being obligatory to design.

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    Re: Oscillator not oscillatiing

    Simulation or real hardware problem?



    •   Alt2nd October 2016, 18:38

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    Re: Oscillator not oscillatiing

    simulation



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    Re: Oscillator not oscillatiing

    Try a "preamble" of ramping the Vcc supply from zero to its
    final value in (say) 1mS.

    Very long timescales may not play well with the macromodel,
    movement of nodes within a timestep may be less than the
    tolerances.

    The timing resistor values are very far from each other, I
    know this is required to approach 50% duty but there's not
    much room from 50% duty to outright fail (deadband exceeds
    ramp amplitude). If you could tolerate (say) 45%/55% or even
    more asymmetry, might try that out just to see if it's a
    limits-of-functionality type problem.

    You could also add a "kicker" current pulse at the beginning
    of simulation to see if that's all it needs to get off the DC
    solution point.



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    Re: Oscillator not oscillatiing

    Circuit oscillates within Multisim as designed perhaps buggy LTSpice doesn't incorporate as much as the former software. Perhaps a miswiring issue:

    Click image for larger version. 

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    Last edited by Zak28; 2nd October 2016 at 19:41.



    •   Alt2nd October 2016, 19:35

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    Re: Oscillator not oscillatiing

    No idea what you did. Circuit works well in LTspice.



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    Re: Oscillator not oscillatiing

    Try starting power at zero or skip initial operating point (.op).

    - - - Updated - - -

    Quote Originally Posted by Zak28 View Post
    Circuit oscillates within Multisim as designed perhaps buggy LTSpice doesn't incorporate as much as the former software. Perhaps a miswiring issue:
    What do you mean "buggy LTspice"??
    Zapper
    Curmudgeon Elektroniker



  8. #8
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    Re: Oscillator not oscillatiing

    Skip initial transient analysis is only useful and possibly needed for simulation of linear oscillators like LC or phaseshift. Relaxation oscillators like NE555 don't have a stable operation point and always start oscillating without specific means.



    •   Alt3rd October 2016, 09:00

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  9. #9
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    Re: Oscillator not oscillatiing

    Quote Originally Posted by crutschow View Post
    Try starting power at zero or skip initial operating point (.op).

    - - - Updated - - -

    What do you mean "buggy LTspice"??
    Exactly;
    Considering that this is a free offering, I find LTSpice surprisingly stable, and simple to use. Have used it for almost 10 years now.

    Any time on which I have had problems, I eventually find that there is a feature that I did not understand, an incomplete third party model, or I did an error during the setup.
    My batteries are recharged by "Helpful Post" ratings.
    If you feel that I've helped you, please indicate it as a Helpful Post



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    Re: Oscillator not oscillatiing

    The 555 oscillator works in LTSpice because I remedied several simple issues however just for a note I found using an LTC6995-1 timer much more convenient and replaced the 555 IC with LT's IC as it requires far less parts and has better waveform characteristics which the 555 IC does not have.



  11. #11
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    Re: Oscillator not oscillatiing

    The 555 oscillator works in LTSpice because I remedied several simple issues
    Simply unclear what your problem was. The LTspice 555 model worked for me from the start with the component values in your post.

    My conclusions so far:
    - There's no LTspice bug involved with the reported problem nor an issue with the LTspice provided 555 model.
    - We still don't know which simulation circuit was not "working" and why.



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