Hi all,

I've been playing with gnucap for a week.... but can't seem to get a test opamp integrator circuit to work. Actually I can't get any circuit with more than 2 non-linear elements to work. The circuit in question is a basic integration circuit using an LM741 opamp, two resistors, one capacitor, and a voltage controlled switch.

The input should be a long pulse, and the output should be a ramp.


When I try to run the analysis, I get: ....       
did not converge
 27.       
did not converge
very backward time step
convergence failure, reducing (itl4)
newtime=5.960464e-13  rejectedtime=1.192093e-12  oldtime=0.000000e+00  using=1.000000e-12
tried everything, still doesn't work, giving up
.....
or in other words, it bombs.


I've attached my p.sch file.

I'm running gnucap 0.35 on debian 6 with emacs 23.


I should preface this with the disclaimer that I know enough electromic to be dangerous..... but I'm trying to learn...


I've been using the Makefile method of Johannes Bauer.


Here's the data on what I'm doing:

* Contents of p.hdr follow:
.include ../models/LM741_NS.mod
..model swmod SW( von=1.0 voff=0.5)
Vss (Vss 0) DC 0 AC 26 SIN(0 26 60hz)
Vdc (+12V 0) DC 12
Vdc (0 -12V) DC 12
Vee (Vee 0) pulse( 0 10 0.5 4 10m 10m)
S1 +12V Vpin Vee 0 swmod


* Contents of p.net follow:
S1 +12V Vpin Vee 0 swmod
R5 Vc 0 10K
X1 0 Vb +12V 0 Vc LM741
C1 Vb Vc 0.00001
R1 Vpin Vb 25K

* Contents of p.sim follow:
.print tran v(Vpin) v(Va) v(Vb) v(Vc) v(Vee)
.op
.tran 0 8 0.001 >p.out
.ends

Can anyone tell me what I'm doing wrong?
Thanks,
Marty