Pspice simulation problem

Thread Starter

laguna92651

Joined Mar 29, 2008
101
I have a simple circuit 2v supply R and Diode in Pspice that I'm trying to run a simulation on. I get the following message when I press run.

"This action cannot be completed because the other program is busy. Choose 'Switch To' to activate the busy program and correct the problem."

I have no idea what the other program is they are referring to. When I choose 'Switch To' button my Vista Start menu comes up.

The Pspice forum doesn't seem to be too active, does anyone know of a more helpful Pspice forum.

Thanks
 

SgtWookie

Joined Jul 17, 2007
22,201
What program are you using for SPICE simulations?

The first thing I would suggest doing is to save your simulation, shut down completely and then re-boot your computer. Then try it again.

There may be another copy of the simulator running in another window and you just don't see it, or memory may be corrupted. Tough to say. Re-booting often cures many ills.
 

Thread Starter

laguna92651

Joined Mar 29, 2008
101
Haven't reinstalled yet, but got pspice running on my laptop.

Simulation works on laptop. I have a simple R Diode circuit to simulate. I want to change some of the characteristics of the diode, Isat and V diode turn-on. I'm using a 1N914, where do I change characteristics? Tried the propety editor, but don't see any place there to make change.
 

SgtWookie

Joined Jul 17, 2007
22,201
I have no clue, since I don't know what PSPICE program you're using.

SPICE was originally programmed on a mainframe computer. PSPICE is basically similar algorythms that were ported over to run on a personal computer. There are many, many different PSPICE circuit emulators. The SPICE directives they use are all very similar if not identical, but the underlying software is coded differently.
 

Thread Starter

laguna92651

Joined Mar 29, 2008
101
I am using OrCad the term Breakout library doesn't sound familiar. but I am use a diode, 1N914, from the supplied librar, Eval library.
 

nanovate

Joined May 7, 2007
665
There should be a breakout library where the models are editable. the other option is to creat a new part with your custom model.

I haven't used OrCAD in awhile. LTSPICE/SwitcherCAD from Linear Technology is much easier to use in this respect-- just drop the SPICE model down on schematic and point to it.
 

Thread Starter

laguna92651

Joined Mar 29, 2008
101
Thanks
I'm brand new to pspice, just installed. You don't have to know the actual name of the library do you?
 

Thread Starter

laguna92651

Joined Mar 29, 2008
101
I found the breakout library, but don't see how to modify Isat and Vcut-in when I go to the Edit Properties. Any ideas?
 

n9352527

Joined Oct 14, 2005
1,198
Have a look at this page http://www.allaboutcircuits.com/vol_3/chpt_3/14.html. The model parameters do not exactly correspond to datasheet parameters. You could try changing a few parameters, like IS, N or RS so that you have a IF against VF curve according to your requirement, hovewer you have to realise that other characteristics of the diode would also be different.

Furthermore, each parameters in the model might seem relate to or describe a physical semiconductor property, but in practice most models are developed with curve fitting methods instead, so changing one parameter might not result like what you expect.
 
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Thread Starter

laguna92651

Joined Mar 29, 2008
101
Wonderful, that is exactly what I was looking for next.

In the SPICE parameter list given it doesn't define VJ, I assume VJ is the cut-in voltage to turn the diode on, is that correct?
 

n9352527

Joined Oct 14, 2005
1,198
VJ is the junction potential. As I wrote in my earlier post, there's rarely one to one correlation between a SPICE parameter and actual physical characteristic. Changing VJ will change the cut-off voltage, but also a lot of other characteristics.

The best method to achieve what you required, as outlined in the referenced page, is to change the SPICE parameters and re-simulate and compare the transfer curve against the one that you want. Not a fun processes, you might need to perform a lot of iterations to achieve suitable transfer curve. Note that this method has to be done separately for AC parameters if you also simulate AC response.

Try changing IS, N, RS and VJ and see the resulting curves.
 
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