In the last hour I’ve been fiddling a bit and got something working in KiCad:
Edit: I’m feeling a bit silly about the Alternative Node Sequence not working. Holger (in post 23 of this thread) had the correct answer.
For me the asymmetry does not matter much. It’s mostly a difference in startup time of either 13ms or 24ms.
But getting anything to work in spice is always a struggle for me and lots of hurdles to overcome. The Spice model I used, I found on my SSD. in the location: ~/projects/kicad/spice/KiCad-Spice-Library/Models/Manufacturer/TRT-Electronics/2n3904.lib (Copied and zipped with the project below.)
You can also find 4 different spice models for this transistor on the Onsemi Website but those all have some copyright notice which confuses me. Why publish that data at all when it’s copyrighted, What does that copyright mean?
For example the “SP2 model”
**************************************
* Model Generated by MODPEX *
*Copyright(c) Symmetry Design Systems*
* All Rights Reserved *
* UNPUBLISHED LICENSED SOFTWARE *
* Contains Proprietary Information *
* Which is The Property of *
* SYMMETRY OR ITS LICENSORS *
*Commercial Use or Resale Restricted *
* by Symmetry License Agreement *
**************************************
* Model generated on Aug 7, 01
* MODEL FORMAT: SPICE2
*$
.MODEL q2n3904 npn
+IS=1.26532e-10 BF=206.302 NF=1.5 VAF=1000
+IKF=0.0272221 ISE=2.30771e-09 NE=3.31052 BR=20.6302
+NR=2.89609 VAR=9.39809 IKR=0.272221 ISC=2.30771e-09
+NC=1.9876 RB=5.8376 IRB=50.3624 RBM=0.634251
+RE=0.0001 RC=2.65711 XTB=0.1 XTI=1
+EG=1.05 CJE=4.64214e-12 VJE=0.4 MJE=0.256227
+TF=4.19578e-10 XTF=0.906167 VTF=8.75418 ITF=0.0105823
+CJC=3.76961e-12 VJC=0.4 MJC=0.238109 XCJC=0.8
+FC=0.512134 CJS=0 VJS=0.75 MJS=0.5
+TR=6.82023e-08 PTF=0 KF=0 AF=1
At least it’s safe to say I have no commercial interest in this. But does it mean I can not sell my astable anymore? It’s a yucky world we live in.
Also note the transistors are upside down. I fiddled a bit with “alternate node sequence”, but (again) did not get that to work.
I’m also getting some weird stuff:
I’ve never been able to do anything useful with spice. I always bump into so many issues that I start second guessing whether the stuff I see in the simulation has any usable correlation with reality.
2022-11-22_astable.zip (7.7 KB)
Edit:
A new version with the transistors “normal side up” and a working Alternative Node Sequence.
I’ve also connected all 4 resistors to the power supply as is more common by the astable Multi Vibrator. It also starts immediately now with maybe just some asymmetry in the first cycle.
2022-11-22T23:06_astable.zip (8.1 KB)