Hello,
I am looking for a referance for using algebraic expressions in LTspice, specificly in subcircuits.

 

Hello,
I am looking for a referance for using algebraic expressions in LTspice, specificly in subcircuits.

LTspice Help file is the authoritative source.

 

The help file won't help with this. Have you looked? Where is it?

 

The help file won't help with this. Have you looked? Where is it?

You state that the help file won't help with this, but then ask where to find the help file.

There are several contexts in which you can use expressions and the constraints differ with each.

What, precisely, are you trying to accomplish. Give a concrete example and let's see if we can figure out if it can be done and, if so, how. If not, what the issue is that is preventing it.

 

I just looked at the help file under subciruits and finally understood it.

 

I am trying to make a spark gap subciruit based on Paschen's Law.

 

Do you want to see what I have so far?

 

It would be interesting to see what you were trying to accomplish and how you ended up doing it -- and how well it is working for you. But there's certainly no requirement.

 

.subckt sparkgap p n

* Parameters
* d: Gap distance in meters
* aa: Gap area in sqr meters
* p: Gas pressure in Pascals, 1 atmos = 101325 pascals

*Gas A B
*Dry air 43.6 * 10^6 12.8
*Argon 10.7 * 10^6 11.4
*Helium 2.32 * 10^6 10.2
*Nitrogen 37.1 * 10^6 12.3


* Model constants
.param A = 43.6e+3
.param B = 23.8
.param C = 11.6

* Spark gap voltage
*Vspark = ({B} * {p} * {d}) / log({A} * {p} * {d}) - log(log(1+(1/1.2)))-{C}

* Capacitance of gap
* Spark gap resistance
Cspark p n {8.85e-12 * aa / d}
Rspark p n {30e15 / (({B} * {p} * {d}) / log({A} * {p} * {d}) - log(log(1+(1/1.2)))-{C})}

.ends sparkgap

 

On the models attribute editor I would pasted "p=101325 d=3e-3 aa=100e-6" on spice line 1.