Most frequently asked questions for beginners
Q: What are the different LTspice file types?
Schematic: name.asc the drawing with your circuit (a text file) Symbol: name.asy symbols for the schematic (a text file) Netlist: name.net unprocessed netlist (text file viewable from within LTspice & usable by other SPICE engines) Logfile: name.log info and results from .four, .measure, .op (text file viewable from within LTspice) may also contain the fully processed and expanded netlist (a Control Panel setting) Result: name.raw binary output data file (text format may be optionally specified) Result: name.fft binary result of an FFT Plot settings: name.plt text file used to save and restore Waveform Viewer plot settings Model file: abc.xyz text file containing model(s) - may be any valid file name Circuit file: name.cir frequently used extension for an external netlist input file (text)
Q: How do you copy and paste between schematics?
A: Click the Copy Icon in the tool bar or select Copy from the Edit drop down menu (or type ctrl-C). Select (with the mouse) what you want to copy. Make the target schematic active (click on it or its tab or type ctrl-Tab) and then click the Paste Icon in the tool bar or select Paste from the Edit drop down menu (or type ctrl-V).
Q: How do I copy and paste between symbols in the symbol editor?
A: It is not possible to use copy and paste in the symbol editor. Symbol files are ascii text. Merge the text as described in message 7201 in the LTspice Yahoo Group.
Q: How can I add intrinsic device models (BJTs, FETs, etc.) to LTspice?
A: Please take a look to the many examples in the files section of the LTspice Yahoo Group (Files => Lib).
Q: How can I add subcircuits to LTspice?
A: You will find many answers when you search the LTspice Yahoo Group messages for words like "library", "symbol" or "FAQ".
Please read first the programs help: Help -> Schematic Capture -> Editing Components -> Creating New Symbols Help -> Help Topics ->FAQs -> Third party models Help -> Help Topics ->FAQs -> Mosfet You will find also help in the linked documents from our LTspice Yahoo Group. Links Links -> Spice Courseware And Tutorials There is another document about symbols and models in our Files section. Files -> Tut -> Symbol Types For Subcircuits
Q: I have a pulse source in my schematic with zero transition times. LTspice only shows slow transition times of 2ns. What's going on here?
PULSE(0 5 0 0 0 20n 100n)
A: LTspice automatically will use a default value for <trise> and <tfall> if these parameters are set to zero. Default value: 10% of Ton or 10% of Tperiod-Ton whatever is smaller. You must specify Trise and Tfall if you want a certain value.
PULSE(0 5 0 100p 100p 20n 100n)
Don't use steeper transitions than required by your application.
Q: I have used a pure sine source in my schematic, but the output signal of my circuit looks slightly different from cycle to cycle.
A: LTspice has waveform compression enabled as the default setting. This compression reduces the amount of saved data during the simulation. It's a lossy compression and thus it can distort the saved signals. You can switch it off with the following command line in your schematic.
.options plotwinsize=0
It could be switched off in the "Control Panel -> Compression" pane as well, but this setting will be lost upon closing the current session of LTspice.