[Help-gnucap] Convergence error

[Jose Roberto B. de A. Monteiro]

Hi list,

I have a convergence error im my simulation. Basically, I have to  work
with switchmode circuits. I am trying to build a simple sawtooth
generator using a current source, a capacitor and a voltage controled
switch, with a non-zero RON.

The circuit is like the following:

* circ-3
* Spice netlister for gnetlist
SW1 1 0 1 0 SWITCH1
C1 1 0 1n
I1 0 1 100u
.model npn npn
.MODEL SWITCH1 SW VT=2.5 VH=2.475 RON=1 ROFF=10MEG
.print tran V(C1)
.tran 0 200e-6 500e-9 UIC >circ-3.dat
.END

The error, after "gnucap -b circ-3.cir":

Gnucap 2005.06.10 RCS 25.28
The Gnu Circuit Analysis Package
Never trust any version less than 1.0
Copyright 1982-2002, Albert Davis
Gnucap comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome
to redistribute it under certain conditions
according to the GNU General Public License.
See the file "COPYING" for details.
* circ-3
very backward time step
convergence failure (itl4)
newtime=4.987417e-05  rejectedtime=4.987417e-05  oldtime=4.987417e-05 
using=4.987417e-05
zero time step
newtime=4.987417e-05  rejectedtime=4.987417e-05  oldtime=4.987417e-05
internal error: step control (adt=1e-12,rdt=-5.36442e-13)
time0=4.98742e-05  time1=4.98742e-05  rtime=4.98742e-05

Maybe because I am not using the lastest GNUCAP... or is there an option
to control the integration step, or to solve this problem? I look for it
in the GNUCAP manual with no success.

Regards
JRM