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[SOLVED] Oscillator not oscillatiing

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Zak28

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

Circuit Untitled.png

Cannot figure this, the specification being obligatory to design.
 

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.
 

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

Untitled.png
 
Last edited:

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

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

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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"?? :???:
 

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.
 

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.
 

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.
 

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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