# Just trying to keep the SPICE flowing. >:) Laser diodes...

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#### zoodlewurdle

##### New Member
Please can someone help me with this? Consider it a fishing lesson, I'm all for catching my own fish when I know how.

I have a laser diode model from an EDN publication, attached PDF file.. It's from EDN so is likely well-tested and fully and simply explained, but I still can't see how to convert to LTspice based on what I've learned this week.

Here's the net list typed out to save time and effort:

Code:
Vlas 100 50 1
Dlas 50 200 diode1

F1 0 1 Vlas 1
Rs 1 0 {Sm*sps}

I1 2 0 {Sm*sps*Ith*exp((T/25)-1)}
G1 0 2 1 0 1
Rlim 2 0 1Meg
Ds 2 3 diode
Vm 3 0 0

F2 300 400 Vm 1
Dmon 300 400 diode
Cmon 300 400 Cmon

.model diode d
.model diode d rs=5

.ENDS
LTspice shows errors suggesting it's not complete, and I'm sure it isn't, the model in the PDF probably has to translate somehow to lines in a .sub file that include that net list and begin with a .subckt line defining a name and the main nodes/pins it has. There also seem to be some odd brackets in that netlist. I copied it VERY carefully but it looks like LTspice isn't having any...

If someone can do me a complete working set of asy and sub files for this, please do. You won't be wasting your efforts, I'll be picking it open to see how it works so I can do it myself next time. Given the scarcity of working laser diode models ANYWHERE you'll certainly please more than me if you do this.

The EDN file:

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#### zoodlewurdle

##### New Member
How does that answer my question? Did you read it? Did you look at the attached PDF to see the drawn model there and see why it is that there are brackets in the netlist that LTspice apparently does not like?

I didn't know how to write an .include directive last week but I did before you posted, and that wasn't what I asked. There's a lot more to this than you saw.

#### ericgibbs

##### Well-Known Member
How does that answer my question? Did you read it? Did you look at the attached PDF to see the drawn model there and see why it is that there are brackets in the netlist that LTspice apparently does not like?

I didn't know how to write an .include directive last week but I did before you posted, and that wasn't what I asked. There's a lot more to this than you saw.
hi,
Do you mean the {} ' braces.?

These braces are important in the expression for parameter substitution.
Look at this extract from the LTS Help files,, Search braces

Did you manage to get the Laser working.?

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#### zoodlewurdle

##### New Member
Hmm.... 'braces'.. At least I now know how to look them up. No, not working yet though. I think the braces are purely to allow the multiplication operator * (as explained in a second page that braces relates to in the CHM file). but the netlist isn't enough of a .sub file to make LTspice happy. There's a whole load of undefined variables in there that are presumably defined in the circuit shown in that PDF (halfway through file, it contains other short articles).

As far as I can make out from further reading yesterday, I need to build that circuit and label it and convert it to a subcircuit that way. Is this right? Nothing has told me this directly so I need more than just confirmation. I'm deducing that this is the way because I can't imagine any other unless it's possible (and easy) to directly write text based on what I see in that circuit.

EDN being EDN, this thing is probably complete and tells me all the info I need, but is it? I don't know enough to know. If I'm going to work at this I want to know if it is useful work. Is it possible to create working asy and sub files for LTspice based solely on that article?

#### ericgibbs

##### Well-Known Member
Hmm.... 'braces'.. At least I now know how to look them up. No, not working yet though. I think the braces are purely to allow the multiplication operator * (as explained in a second page that braces relates to in the CHM file). but the netlist isn't enough of a .sub file to make LTspice happy. There's a whole load of undefined variables in there that are presumably defined in the circuit shown in that PDF (halfway through file, it contains other short articles).

As far as I can make out from further reading yesterday, I need to build that circuit and label it and convert it to a subcircuit that way. Is this right? Nothing has told me this directly so I need more than just confirmation. I'm deducing that this is the way because I can't imagine any other unless it's possible (and easy) to directly write text based on what I see in that circuit.

EDN being EDN, this thing is probably complete and tells me all the info I need, but is it? I don't know enough to know. If I'm going to work at this I want to know if it is useful work. Is it possible to create working asy and sub files for LTspice based solely on that article?
hi ZW,
Im tied up on another project at the moment, but I would be interested if you can get the laser file working.

I have only been using LTspice for a few weeks, but I'm a quick study.

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