Simulators and convergence

rtarbell · 13th June 2006, 04:15 AM

Regarding simulators (Pspice, TopSpice, SwitcherCad, etc.),

Let us say I have a circuit that will not converge when simulated on an older computer.

==> Is there a chance that, using the exact same simulation program, the same circuit WILL converge on a more powerful computer (i.e. faster, more RAM, etc.)?

HFGuy · 13th June 2006, 04:38 AM

nope, the solution sets arnt closing to a single value (converging to a single answer). It has nothing to do with your computer.

jcx · 13th June 2006, 04:42 AM

LtSpice is supposed to be pretty good on convergence - the more recent versions have added a gshunt hack that lets you add a conductance from every node to gnd - sometimes helpful

did you try the ps ramping hack? - replace your supplies with pwl sources that start a 0 - surely it can find an operating point - then ramp the sources to the operating V, this can still get to non-physical states but sometimes works

ideal current sources can run off to KV, volatage sources can supply KA - clamping diodes on ccs to ps helps me occasionally

HFGuy · 13th June 2006, 05:21 AM

Or switch to Cadence, ive yet to have it not converge on me

I_Forgot · 13th June 2006, 07:22 AM

Quote:

Originally posted by HFGuy
Or switch to Cadence, ive yet to have it not converge on me

SwitcherCAD (aka LTSpice) is free. Most of us could not afford the annual maintenance contract, let alone the cost of a license, for Cadence.

I_F

TwoSpoons · 14th June 2006, 11:32 PM

Simetrix always converges for me. You can also change the integration method - fast and loose or slow and accurate. You may also find using a smaller timestep on transient sims will work better. Also setting up your initial conditions better will help. Sometimes adding a small resistor in series with reactive elements (l and C) can help too.

Curmudgeon · 15th June 2006, 08:04 PM

On earlier pspice variants that I used, the above suggestions were helpful; also changing the starting conditions could cause convergence to a different answer, sometimes a better one.

13th June 2006, 04:15 AM	#1
rtarbell diyAudio Member Join Date: Sep 2005	Simulators and convergence Regarding simulators (Pspice, TopSpice, SwitcherCad, etc.), Let us say I have a circuit that will not converge when simulated on an older computer. ==> Is there a chance that, using the exact same simulation program, the same circuit WILL converge on a more powerful computer (i.e. faster, more RAM, etc.)?

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13th June 2006, 04:38 AM	#2
HFGuy diyAudio Member Join Date: Sep 2004 Location: Toronto, Ontario	nope, the solution sets arnt closing to a single value (converging to a single answer). It has nothing to do with your computer.

13th June 2006, 04:42 AM	#3
jcx diyAudio Member Join Date: Feb 2003 Location: ..	LtSpice is supposed to be pretty good on convergence - the more recent versions have added a gshunt hack that lets you add a conductance from every node to gnd - sometimes helpful did you try the ps ramping hack? - replace your supplies with pwl sources that start a 0 - surely it can find an operating point - then ramp the sources to the operating V, this can still get to non-physical states but sometimes works ideal current sources can run off to KV, volatage sources can supply KA - clamping diodes on ccs to ps helps me occasionally

13th June 2006, 05:21 AM	#4
HFGuy diyAudio Member Join Date: Sep 2004 Location: Toronto, Ontario	Or switch to Cadence, ive yet to have it not converge on me

14th June 2006, 11:32 PM	#6
TwoSpoons diyAudio Member Join Date: Oct 2004	Simetrix always converges for me. You can also change the integration method - fast and loose or slow and accurate. You may also find using a smaller timestep on transient sims will work better. Also setting up your initial conditions better will help. Sometimes adding a small resistor in series with reactive elements (l and C) can help too.

15th June 2006, 08:04 PM	#7
Curmudgeon diyAudio Member Join Date: Nov 2005	On earlier pspice variants that I used, the above suggestions were helpful; also changing the starting conditions could cause convergence to a different answer, sometimes a better one.

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