# Helpfull tip: Import new model for LTSpice

#### FuzzballJack

Joined Apr 12, 2014
13
As a beginner in LTSpiceVI I have had a lot of problems implementing a new model into the simulator.
I will be going over the cause of my problem in this thread. This is only for inexperienced LTSpice users. I hope to help fellow LTSpice starters so they don't struggle with the same problem I had.

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So you just installed LTSpice, ready to begin cranking out some simulations but can't find the model for a component? Let's say you need a UA741 General purpose Op-amp.

You go on-line and find the model for it. It is usually some text file with a whole bunch of code (gibberish for newb spicers).

Then you slam that puppy into spice like it is shown on the forum you got the code from. Finally sit back and press that "run simulation"-button like a boss and get startled by a strange error.

Rich (BB code):
Unknown subcircuit called in: ...
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This has been a pain for me from the start. Ever since I started using LTSpice I have had this problem and not a single forum that could point me in the right direction.
But now I found what the problem is!

All the steps you need to complete:

1. Find the model code online for the item you want to model.
2. Save the code in the folder LTspiceIV\lib\sub as a .lib file
3. Include the lib directive in your drawing (press the .op button in Spice) through ".lib <lib-name-you-saved>"
5. Change the value of the component to the name of the component you just added
Now, step 5 is where I have made some errors.
Remember the .lib file you added to the spice lib folder? Open it with notepad. Search for a line that starts with

Rich (BB code):
..SUBCKT
and ends with some numbers. The value between the ..SUBCKT and the numbers is the value for your component you want.

To conclude:

• The filename of the .lib file is the one you need to import in the drawing
• The partname you find inside the file is the name you need for the part value.

For example:

• I needed to import ".lib LM741.lib" because my file was named "LM741.lib"
• And I needed to rename the value of the component to "XUA741" because the partname inside the file was "XUA741"

Or you can name the 2 exactly the same if you are smart to make things easier.
Hope I helped!

Fuzz.