Go to the Linear Technology Designtools Software page. The links to download LTspice and the guides are in the first box.
The “Download LTspice IV” link (10 MB) is the first in the box. When you click on it you will be asked if you want to register, but the fastest way to get your LTspice is to select “No thanks, just download the software”.
For an introduction to LTspice you can look at the LTspice Users Guide and the LTspice Getting Started Guide (the links are in the same box as the LTspice simulator). But if you are impatient, here are the minimum steps that you need to start with the simulation:
First choose "File / Open" and select the circuit that you want to simulate. A circuit where you can see some interesting waveforms is the “astable” circuit in the "examples/Educational" folder (an astable multivibrator that is built with two transistors). Then choose "Simulate / Run". Now click on the node in the schematic for which you want to see the waveform - ready !
Now you can start to play with the circuit: Right-click on one of the components and a window will pop-up where you can change the value of the component. You will immediately see the new value in the schematic. If you now choose "Simulate / Run" again, you will see the effects that changed value has on the selected waveform.
The best circuit examples - especially for the beginner - are in the "Educational" folder. Some of them do not only show interesting circuits, but also special simulation features, for example the "Monte Carlo" file. If you already have some experience, you should also look at the "jigs" folder. Here you will find several application examples for Linear Technology devices.
You may also be interested in some other Recommendations for Circuit Simulations with SPICE.
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