Hysteresis for the SW in LTspice question

Den onsdag den 25. december 2013 20.31.42 UTC+1 skrev Maynard A. Philbrook Jr.:

would the neonbulb with changed voltages work ?

-Lasse

Often you need to force a maximum time step to get LTspice to find a solution... its defaults are too loose for negative resistance situations. ...Jim Thompson

Level 1 Vh positive:

Switches abruptly at Vt-Vh and Vt+Vh Hence Vt=1 and Vh=0.5 will switch at 0.5 and 1.5 Vt midway between switching points.

Level 1 Vh negative:

Switches smoothly (polynomial fit) at Vt-Vh and Vt+Vh

/Examples/Educational/Vswitch.asc demonstrates this. You need to play with the .model directive to see the two modes As it comes, it uses Vh negative. Play with it to see how it works. This is what most people ever need.

Putting "level=2" in the .model line, with Vh negative gives a function dependent on log(Roff/Ron)/pi, and log(1/(Roff*Ron))/2, with a tanh limit function. Jim would like that ;-) You probably never need worry about level 2.

It's all in the help file, just not either intuitive, or well explained.

LTspice also appears to honor Pspice switch syntax, which is different, too.

Yup

Par for the course.

See above

Post the relevant .asc, and let's see what can be done.

Like a spark plug?

Sorry, that's misleading/ambiguous.

Hence Vt=1 and Vh=0.5 will switch at 0.5 and 1.5V. Vt is midway between switching points.

That's better;-)

I got it, it appears that the Vh parameter plays two roles here. - numbers creates arc intersection, much like an arc-cardinal function which can form an arc wave in the load effect of the switch. Setting the Vt and Vh -0..-1 sets the arc and offset for the Vt. I guess one could use that to make selectable raise/fall rates.

Using positive numbers does the OFFSET of the Vt (trigger). This means If i would to do this, Vh = 1, that would put the Vt at Vt+1 and Vt-1 etc, which makes sense. but the help file does not explain this to you.

Jamie

That's just a verbatim reprint of the help file

Yes, indeed!

...Jim Thompson

It actually does explain it, just not very well.

See the PDF I posted to a.b.s.e, which illustrates the various modes as plots of switch impedance versus control voltage.