type (the unknown target, in many
cases). Unknown design questions can
be answered and data collected
before the final project is attempted.
What does this have to do with hobby
electronics and SPICE? Hopefully,
we’ve added a few technical terms
and some background to make it
easier to understand the SPICE world
(hint: element, model, simulation).
These terms will appear in SPICE work,
and each has a specific meaning and
job to do.
■ FIGURE 1. SwitcherCAD
III/LTspice start-up screenshot.
Virtual Simulator
We’ve talked about physical
machine simulators, but simulation can
also be done in a totally artificial environment inside a computer, where the
output is the result of mathematic
operations performed upon initial data
using rules that mimic the
behavior of the real world
materials. Simulations speed
up the design cycle and
reduce costs, and those
advantages apply directly to
all of us. Now we’re getting
closer to electronics! Take
the principles of electronic
circuits, the behavior of the
components, add a schematic and power supplies, input controls
and signals, add a little SPICE, and see
what comes out!
Jumping In With
Both Feet
That’s enough background to set
the stage. Let’s try to do something
simple with LTspice. Take another look
at the sidebar, download the software,
and set it up on your own PC. Next,
start the program and compare your
screen to Figure 1. Hit the File > New
Schematic button on the toolbar to
start a new project, and notice that
Getting Started With LTspice
I use a typical PC running a Microsoft OS. I’m not
sure if the LTspice software can run on other platforms.
A fast machine (Pentium4, 2 GHz or higher) is very
desirable as SPICE work hogs both memory and CPU
time. The software is a free download from the Linear
Technology (LTC) website at www.linear.com/design
tools/software/switchercad.jsp.
The tool is one of several that LTC offers, and seems
to have two names: LTspice and SwitcherCADIII. As far as
I can tell, they are one and the same; to avoid confusion,
I’ll call it LTspice (except where another name is critical,
such as files and directory names). Users have the option
of registering with LTC for email notification of updates,
and also to download other software and device libraries
(recommended).
The file is about eight megabytes (it varies with
updates: at the time of writing the version is 2.24u
and dated 7/8/08). I recommend
downloading and saving the file to a
new temporary subdirectory, then running it so if
anything goes wrong (or you move it to another
computer later), you already have the file saved.
There is a legal agreement screen that requires
acceptance, and the default installation is to a new
subdirectory called LTC in your computer’s Program Files
directory. (See Figure A.) If you have already installed a
previous version, it prompts before overwriting it
(recommended). There’s quite a bit to the automatic
installation, so be patient! (Also, it’s better to not tax your
computer by running other programs during installation.)
When the installation has finished (Figure B), you may
run the program and, for future ease, add the LTC spice icon
to your computer’s start menu (or desktop). The download
also includes subdirectories for examples and lib (library);
the LTC directory should look something like Figure C.
Next, navigate to the Nuts &Volts website with your
browser and download the companion file for this article.
Unzip the file to a local directory. (You can use the same
subdirectory as the LTspice install
(Figure C again) and put the article
files and your new work in a fresh
subdirectory. (I call mine NandV.)
Figure B
Figure A
Figure C
December 2008 51