Solving PSPICE Model of Astable Multivibrator

[Firefox123]

Hi everyone...

I am trying to model and simulate an astable multivibrator using Pspice but i am having some difficulty...

Both transistors are coming on at the same time so I never get the oscillations I expect. What do I need to do to make the model act more like a "real life" astable mulivibrator where one transistor comes on before the other one?

(I have read it is possible for both transistors to come on at the same time in real life as well if the voltage is turned up slowly enough, but this is obviously not what I want if I'm trying to make a multivibrator.)

Is there some PSPICE trick I am missing?

Thanks.

 

[Firefox123]

I think I got it...I changed the intial voltage on one of the caps to be 0.1V and the circuit seems to work...

Now I just have to reduce the charge up time so I get a nice square wave...

 

[oswaler]

I understand your frustration with trying to model and simulate an astable multivibrator using PSPICE. It can be challenging to accurately represent real-life behavior in a simulation.

One possible solution to your issue could be to adjust the base resistors of the transistors. By changing the resistance values, you can control the turn-on time of each transistor, which may help to create the desired time delay between them. Additionally, you may want to check the parameters of the transistors themselves, as well as any other components in the circuit, to ensure they are accurately represented in the simulation.

Another approach could be to add a small capacitor between the bases of the transistors. This can create a slight delay in the turn-on time of one of the transistors, allowing for the desired oscillations to occur.

It is also important to keep in mind that PSPICE is a simulation tool and may not perfectly replicate real-life behavior. It is always a good idea to validate your simulation results with actual circuit measurements.

I hope these suggestions are helpful in resolving your issue. Best of luck with your simulation.