Why does it give oscillations when Orcad doesnt and it shouldnt?

[Battelle]

Thank you Max; the oscillations have now been removed.  However, the output for the collector of Q5 varies in Pspice and Multisim.  In Multisim, the output is in the -288V range, whereas in Pspice it is -3V (correct value).  I believe that the parts could be different in each simulation, but how do I make them identical, when they already appear to be so?  For example, when I look at the model of Q3 in both the Pspice library and the part properties of Multisim, they are identical:

.model Q2N4401  NPN(Is=26.03f Xti=3 Eg=1.11 Vaf=90.7 Bf=378.9 Ise=183f Ne=1.433
+               Ikf=.3656 Nk=.5 Xtb=1.5 Var=100 Br=1.01 Isc=0 Nc=2 Ikr=0 Rc=.5
+               Cjc=11.01p Mjc=.3763 Vjc=.75 Fc=.5 Cje=24.07p Mje=.3641 Vje=.75
+               Tr=233.7n Tf=466.5p Itf=0 Xtf=0 Vtf=0).

[Maxish]

Battelle,

For that I will really need to know all the parameters pspice uses. How do I even know that your PWL sources are the same?

One thing you can try to do, if you cannot save the orcad file, is to export the output file (which will contain most of the netlist). In the toolbar, go to Pspice->view output file

Thanks,

[lacy]

You are wondering about the -288 V at your test point. I just simulated your second circuit you posted and it looks to me that V5 is not correct. It looks to me that you have it set at -1287V. I am sure this probably was meant to be -12.87. You might want to check this and see if indeed it was a typo. I changed it to -12.87V and at the collector of Q5 I read approx -2.9 Volts DC.

As far as your original oscillations I tried Max's suggestion and it did work, but I had the Simulate>Default Instrument Settings>Set to Zero enganged and it oscillated with the original C51 until I changed it to 1uF. The oscillation then stopped. I changed this Cap back to it's origianl value and went to Simulate>Default Intrument Settings and set it to Automatically Determine Intial Conditions and it did not oscillate.

So it is up to you as to whether you woukld want to just change the Cap value or change the way the simulator simulates the circuit. It is my opinion that changing the simulator settings will make it work more like your Pspice. This may help in getting simular results between the both of them in the future.

Hope this helps. Have a Nice Day

[Battelle]

Max,

I am trying to import the orcad file (.dsn) in to Multisim.  The parts import and it looks the same, but when you try to run the simulation it states that there are no power sources.  How do I get the actual values to import as well?  Also, The box that lets you edit the model of the transistors is also grayed out so you cannot look at the model to check if they were imported correctly.  Any suggestions?  I have attached the imported file.

Lacy,

The voltage is correct as it is -1287V.  The reason for this is that the model for a diode: 1N5312 was not available in this version of multisim.  Also, when I simulate with automatically determining initial conditions and using the Multisim defaults, the output still oscillates. Is there any way you can send me your file?  Since I have a newer version I should be able to open it right?

~Battelle 

[Maxish]

Battelle,

Attach your orcad .dsn file and I'll have a look

Thanks,

[Battelle]

It will not let me attach the orcad file.  .dsn is not a valid extension.  Is there an email to which to send it or any other medium?

Battelle

[nestor-sg]

You can ZIP the file. Put it in a compressed folder (.zip) and attach it.

[Battelle]

Here is the file.

[lacy]

I am going to attach both circuits. The first is the original and of course the next one is from your second circuit yoyu posted.

I have not changed anything in the first cirucit. The only change to the second is the 1287V which I have as 12.87V.

I am sorry I haven't been much help, but I am only reporting to you what I find when I simulate your circuit even though it may not be what you are looking for. Anyway, I tried. I hope these files help you figure out exactly what is happening.

Have a Nice Day

[lacy]

I forgot that I did change one thing in the first circuit. Like you said the model for 1N5312 isn't in mine either so I used the closest diiode to that I had. I thought I had better mention that in case it changes the results in some way. Sorry about that.