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LTSpice FRA Component?

Category: Software

Hi Everyone,

I've heard LTSpice will add FRA component and I have a few questions:

1. Does the FRA Block uses a different kind of algorithm then the one known of "LTspice: Basic Steps in Generating a Bode Plot of SMPS"?

2. Where can I find the update file because right now after updating to LTSouce XVII ( there is no FRA component.

Thank you.

Top Replies

  • Hi HLevy585,

    I believe you can access that new component in the LTspice 17.1 version which can be downloaded here.

    LTspice 17.1 is a significant upgrade to LTspice XVII, including new features and numerous performance and stability enhancements:

    • Transient Frequency Domain Analysis. LTspice 17.1 includes a new frequency response analyzer component and associate .fra spice directive.
    • Frequency domain analysis has been reduced to a single component and directive, greatly simplifying the generation of Bode plots for non-linear circuits, including switched mode power supplies
    • Both loop gain and output impedance are supported by this feature
    • Improved Installation. LTspice library files are stored in users’ %LOCALAPPDATA% directories, instead of My Documents
    • Waveform Viewer. Faster plotting speed for large datasets
    • Keyboard Shortcuts. Keyboard shortcuts can be saved to and loaded from text files
    • Schematic Capture. Numerous schematic editor bugs have been eradicated
    • Simulator Operation
    • Fixed a number of convergence problems
    • Updated initial conditions behavior and documentation to match behavior
    • Reduced multi-threaded CPU loading

    I am also excited to try this feature.

  • Yes, there is a new release (currently as beta version) which adds FRA. It can be downloaded here:

    The underlying algorithm is similar, but the implementation much faster. It's described in the help file, additional documentation is being worked on. The release also comes with example schematics.

    Best Regards,

  • Thank you for your answer.

    First let me say that it is a very welcome addition to the LTSpice program and as a user I'm glad to see LTSpice advance and adding more features.

    I downloaded and played around with the component, and I have a question about setting up the FRA.

    I would like to do a frequency sweep from 100Hz to 20kHz and  I want to make tsettle (stimulus settling time at each frequency before analysis begins) adaptable to each frequency.

    For example at F = 100Hz make settling time 5/100 and for F=20kHz make settling time = 5/20k. what I want is to make tsettle = 5 / Current Stimulus Frequency. 

    Right now the simulation time is much larger then necessary because the settling time is a function of the lower frequencies and in the higher frequencies there is no need for a large settling time.

    Is there any way to achieve this?

    Thank you!

  • Thank you very much for your answer!

    I posed a question to mborn reply, I would appriciate it if you could take a look at it and answer if you can.

    Thank you!

  • No that's not possible.

    We made it this way because a linear system has a constant settling time that doesn't depend on the stimulus frequency.

    Best Regards,