Helpfull tip: Import new model for LTSpice

Thread Starter


Joined Apr 12, 2014
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.


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).

For example LM741:

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: ...

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>"
  4. Add a comparable component's footprint in your drawing
  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):
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! ;)