LTspice Download, Install, and Updates
Visit analog.com/ltspice to download LTspice. Once you install LTspice, it is important that you keep the software, models, and examples up-to-date.
Check for software updates by clicking Help → Check for LTspice Updates.
To ensure the model and examples libraries are up-to-date, click Tools → Update Components.
Opening an Existing Schematic
It can take some time to learn how to draw a schematic from scratch — an easier first step is to explore a schematic that's already been created. LTspice schematic files have an .asc extension and are available from Analog Devices in several locations.
Download a Demo Circuit
A central repository of demo circuits can be found on the LTspice Demo Circuits page on analog.com. This page allows you to search for LTspice schematic files by application and/or part number.
These demo circuit schematic files can also be found in the Tools & Simulations section of the product pages on analog.com — The AD4000 is an example of a product that has multiple LTspice demo circuits.
Start with a Component Example
LTspice contains a comprehensive library of Analog Devices component models, and most of those components have an example schematic associated with them. These example circuits are a great starting point for drafting schematics since the examples have been designed to ensure the device is set up for a successful simulation (with the required supply voltages, stimulus voltages, and a simulation directive).
These example circuits are usually fairly simple, and do not necessarily represent a target application, or reflect considerations necessary for actual hardware — but they provide a good starting point that can save you time over drafting a schematic from scratch.
To open a component example, you must first create a new schematic by clicking File → New Schematic. Then, to open the Place Component dialog by clicking Edit → Component.
In the Place Component dialog, you can find a device by either navigating to it through the product categories, or you can type the device name to find it. Select the device name you are interested in, and click Open Example Circuit.
Start with an Educational Example
LTspice includes a library of educational examples that are intended to help you explore circuit and simulation concepts. To open an educational example, click File → Open Examples. Navigate into the Educational directory, and select an .asc file to open.
Making Modifications to a Schematic
Creating a schematic from scratch is fairly easy in LTspice - if you want to learn more about how to create simple schematics from scratch, watch our LTspice Basics video series. In this article, we will be focusing on making basic edits to existing schematics.
All schematic editing commands are available under the Edit menu, or by right-clicking the schematic background.
Editing Component Attributes
In most cases, right-clicking the component will allow you to modify the attributes of that component. The component attribute dialog will depend on the type of component you are editing.
Resistors, capacitors, inductors, beads, diodes, and transistors (bipolar, MOSFET, JFET) each have libraries of models where you can select a specific model for that component.
If your device model is not included in the model library, you can use the .MODEL directive to define a custom model for your device. See the help topic for .MODEL in the LTspice Manual for more information about this feature.
Some components have basic and advanced options — The voltage source is an example of this. Right-click on the voltage source to bring up its basic attributes.
Click Advanced to view the additional parametric options for that voltage source.
Entering Units
LTspice follows standard engineering notation for numerical parameters - mostly. LTspice is also case insensitive - because of this, M and m both represent 10-3 (milli). If you want to use the 106 (mega) prefix, you'll need to use MEG or meg.
Also - do not use f or F for farad. Typing 1F will result in a value of 1 femtofarad. For 1 farad, just enter 1.
|
Character
|
What It Means
|
|---|---|
| T or t | tera = 1012 |
| G or g | giga = 109 |
| MEG or meg | mega = 106 |
| K or k | kilo = 103 |
| M or m | milli = 10–3 |
| U or u (LTspice replaces with µ) | micro = 10–6 |
| N or n | nano = 10–9 |
| P or p | pico = 10–12 |
| F or f | femto = 10–15 |
Navigating the Schematic
You can find zoom functionality in the View menu. You can also use the mouse scroll wheel to zoom in and out. You can click and drag to pan to a different area of the schematic. Press the space bar to zoom to fit.
Simulation Commands
Simulation commands are already defined in most educational and component example circuits, so you should be able to run simulations on these example circuits without any additional editing of the schematic.
You can edit an existing simulation directive by selecting Simulate → Configure Analysis in the menu.
Here, you can either modify the existing simulation, or you can switch to a different simulation type by selecting the tab for the simulation you want to run. LTspice simulation directives include transient (.tran), AC (.ac), noise (.noise), DC operating point (.op), DC Sweep (.dc), transfer function (.tf), and transient frequency response (.fra). Transient frequency response is the newest simulation directive in LTspice, which allows you to simulate a frequency response using transient simulation methods.
Run the Simulation
With your example schematic opened, start the simulation by selecting Simulate → Run from the menu. LTspice will use the schematic to generate a netlist and then will simulate that netlist. The netlist can be viewed by selecting View → Spice Netlist from the menu.
Waveform Viewer
Running a simulation will open a blank waveform window. If you are trying to view the netlist, you'll need to click on the schematic window to make it active — this will result in the View menu being available.
Probing your schematic
Once you've run a simulation, you can add traces to the waveform view by clicking directly on this schematic.
Plotting a Voltage
Hover the cursor over wires — if the voltage can be plotted, you'll see the cursor change to a voltage probe cursor.
Click on the wire with the voltage probe, and that voltage (referenced to ground) will be displayed in the waveform viewer.
You can also add traces to the waveform viewer by clicking on the waveform viewer to ensure it's active and then selecting Plot Settings → Add a Trace from the menu.
Plotting a Differential Voltage
To plot a differential voltage, click on a wire with the voltage probe cursor, and drag the cursor to the second voltage that are are using as a reference. After clicking the first wire, the voltage probe will change to black until you click on the second wire.
Plotting a Current
For simple components with only two nodes, you can plot the current by hovering over the component. The cursor will become a current probe cursor.
Click on the component to plot the current through it.
For components with more than two nodes, you can plot the current flowing into a node by clicking on it.
Zooming in on a Waveform
You can click and drag to zoom in on a tighter area of the waveform to zoom into that area. You can return to a fully zoomed-out view by typing space.
Taking Quick Measurements
When clicking and dragging to zoom, you will also see measurements in the bottom left corner. You can use the zoom cursor to make very quick measurements of dx, dy, and slope. Minimize the box before releasing the mouse button to prevent zooming in.
Deleting Traces
To delete traces from the waveform viewer, right-click on the trace label at the top of the waveform viewer and select Delete this Trace.
You can also select Plot Settings → Delete Traces. The cursor will change to the scissors cursor, and you can click on trace labels to delete them. Press Esc or right-click to end the delete functionality and return to the crosshairs cursor.
If you have multiple traces plotted, and want to remove all of them except for one trace, double-click the wire or node on the schematic to remove all other traces.
Other features of the waveform viewer can be explored by viewing the options in the Plot Settings menu (ensure you have the waveform viewer window active to show the Plot Setting menu).
Built-in Help
The LTspice Help Manual is available by selecting Help → LTspice Help. The Help Manual is organized by topic, indexed, and searchable, and is a great starting point for learning more about the various features in LTspice.
Additional Resources
- Visit analog.com/ltspice for technical articles, videos, and example circuits.
- Visit EngineerZone for questions, discussion, and FAQs.