Electronics Computer-Aided Design PSpice and series of capacitors

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Subject Author Date
PSpice and series of capacitors effepe 11-20-07
Posted by effepe on November 20, 2007, 8:10 am
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PSpice get crazy to determine voltages when I have a series of capacitors:

<http://img213.imageshack.us/img213/1521/ex231yg7.gif>

After 'googled' a bit, I tried to fix the limitation of floating pin
(seems that PSpice can't determine DC voltage in such situations) by
adding two shunt resistors (R2 and R3) of huge value (1 TOhm).

In option tab, I enabled GMIN (1E-12 S) too.

Is there a possibility to use PSpice or I have to switch to LT
SwitcherCAD III ?

Still was wondering how a software like PSpice can fall down so poorly
with a simple circuit like this.

Thanks in advance and my apologies for my (surely poor) English ;-)

Posted by Charlie Edmondson on November 20, 2007, 12:01 pm
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effepe wrote:
> PSpice get crazy to determine voltages when I have a series of capacitors:
>
> <http://img213.imageshack.us/img213/1521/ex231yg7.gif>
>
> After 'googled' a bit, I tried to fix the limitation of floating pin
> (seems that PSpice can't determine DC voltage in such situations) by
> adding two shunt resistors (R2 and R3) of huge value (1 TOhm).
>
> In option tab, I enabled GMIN (1E-12 S) too.
>
> Is there a possibility to use PSpice or I have to switch to LT
> SwitcherCAD III ?
>
> Still was wondering how a software like PSpice can fall down so poorly
> with a simple circuit like this.
>
> Thanks in advance and my apologies for my (surely poor) English ;-)
You are going to see the same problems in LTSpice, and just about any
other spice there is. Every node needs to have a DC path to ground for
the differential equations to make sense.

And then, you blew it by putting in a ridiculous resistance like a
teraohm. Usually, 100MEG is more than sufficient, occasionally a full
1G if you need really small shunt currents, but this is a simulator with
a realisitic dynamic range. There aren't real 1T resistances out there,
and they blow up the simulators when you have 1T resistances, and then
really small resistances. Get real, get some experience, and then you
can critize the simulators for real problems...

Charlie

Posted by effepe on November 20, 2007, 1:17 pm
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Charlie Edmondson ha scritto:

>Usually, 100MEG is more than sufficient,

Also using 100MEG, PSpice puts out exotics voltages.

Posted by effepe on November 23, 2007, 11:07 am
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Charlie Edmondson ha scritto:

> You are going to see the same problems in LTSpice,
LTSPice simulate it correctly.

Posted by Jim Thompson on November 23, 2007, 11:16 am
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>Charlie Edmondson ha scritto:
>
>> You are going to see the same problems in LTSpice,
>LTSPice simulate it correctly.

LTspice adds the R's that everyone has mentioned. Likewise series R's
for inductors.

"correctly"?... you are an IDIOT.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave

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