Simple Circuit doesn't converge.

[etech]

Hello,

Can anyone tell me why this simple circuit, attached, doesn't converge?
It produces fatal error:

Initial delta set to 1e-06 @00:00:00.000000
[SPICE] transient GMIN stepping at time=0.000480902 @0.000480902s
[SPICE] transient GMIN stepping at time=0.000480902 @0.000480902s
[SPICE] TRAN: Timestep too small; timestep = 1.25e-019: trouble with node #00008. @0.000480902s
Total Iterations=19100, Total Steps=353, Good Steps=252, Bad Steps=101 @0.000480902s

I'm including the 2N7000 model file I used, but the circuit doesn't work with any 2N7000 mosfets.

Thanks

[Ettore]

Simply configure the SPICE solver for "Settings for Better Convergence". System menu->Set Animation Options->SPICE Options button and finally select "Settings for Better Convergence" from the bottom list and press Load and then OK twice in order to exit.

Also, is there any reason why you did use 2N7000.REV0.SP3 external SPICE model ? Proteus provides a ZETEX model for the 2N7000, which is more stable and works with "Default Settings".

Finally, please drop an e-mail to support@labcenter.com with your customer number if you want to continue getting support on this forum.

[etech]

Simply configure the SPICE solver for "Settings for Better Convergence". System menu->Set Animation Options->SPICE Options button and finally select "Settings for Better Convergence" from the bottom list and press Load and then OK twice in order to exit.

OK...it is converging now. Thank you. I'm still becoming familiar with Proteus.

Also, is there any reason why you did use 2N7000.REV0.SP3 external SPICE model ? Proteus provides a ZETEX model for the 2N7000, which is more stable and works with "Default Settings".

I read that PROSpice is a Spice3 engine. The models I found were spice2 or pspice, that I read are incompatible. So I imported the spice3 model.
Did I misunderstand?

Finally, please drop an e-mail to support@labcenter.com with your customer number if you want to continue getting support on this forum.

OK. I am a licensed user and will do so later.

I do have one more question:
The CD4000 devices have an internal selectable "Model Timing Voltage" parameter. I'm assuming this parameter sets the timings per the supply voltage. I'm using 12v and don't see a value for this voltage. What value should I use?

[Ettore]

...I read that PROSpice is a Spice3 engine. The models I found were spice2 or pspice, that I read are incompatible. So I imported the spice3 model. Did I misunderstand? ...

The point is that you don't need doing that for 2N7000 mosfet as Proteus has one already supported in the standard library. Simply pick it up from library and simulate it.

I do have one more question:
The CD4000 devices have an internal selectable "Model Timing Voltage" parameter. I'm assuming this parameter sets the timings per the supply voltage. I'm using 12v and don't see a value for this voltage. What value should I use?

You can set a close voltage, i.e. 10V is the worst case, but it shouldn't be so critical for such a circuit, TBH.

[etech]

The point is that you don't need doing that for 2N7000 mosfet as Proteus has one already supported in the standard library. Simply pick it up from library and simulate it.

Why does it matter that I used a third party spice model? I should be able to do that.

You can set a close voltage, i.e. 10V is the worst case, but it shouldn't be so critical for such a circuit, TBH.

I never wrote that it was critical. I was simply trying to understand the purpose of the parameter.

[Ettore]

Yep, you may use all third party models you like but this is not guaranted to work with a simulator different than it was developed for or tested with.

Didn't you ask "What value should I use?". Well, 10V is fine.