Simulate electrical and electronic circuits. LT Spice

Introduction

In this article we are going to see how to download and install LT Spice software to simulate electrical and electronic circuits. We will also create a simple circuit to test the program.

Download the software

First we will download the installer from the official website, click on the link below:

LT Spice

*Fig. 1: On the official website we download the program according to our operating system.*

Once the download finishes we run it. In my case I got a screen saying that the installation was blocked by the Windows protection system, when I clicked on “More information” the button “Run anyway” appeared.

*Fig. 3: Windows blocked the installation, clicking on More Information displays the Run anyway button.*

We accept the terms and conditions and choose the installation location. In my case I leave everything by default.

*Fig. 4: First we must accept the terms and conditions of the software.*

*Fig. 5: Choose the installation parameters and click Install Now.*

At the end of the installation the program runs automatically, the sign appears in Figure 6 saying that the program is ready to run for the first time.

*Fig. 6: At the end of the installation, the software prepares for the first run.*

At the end of the process the main window of the program appears, and we are ready to start creating schematics and simulating electrical and electronic circuits.

*Fig. 7: This is the main window of the simulation program*

Create an Schematic

Next we’re going to create a very simple circuit like the one we saw in the article about what electrical resistance is, which consisted of a voltage source and a resistance.

First we go to File > New Schematic, to create a new project, this can be seen in figure 8.

*Fig. 8: To start with we create a new schematic.*

The workspace appears in gray, here we will begin to build the schematic.

Let’s add elements, click on the AND gate button shown in figure 9.

*Fig. 9: Button to add a component to the schematic.*

This will display a window in which we can choose the components.

Power Source

To power our circuit we are going to need a voltage source, in the search bar of the components window we write “voltage” and select the generic source that can be seen in figure 10.

*Fig. 10: In the window that appears write “Voltage”.*

We place it in the workspace and right click on it, this will open a window to enter the parameters of the font, in my case I will use 5 Volts.

The “Advanced” button allows us to define advanced parameters of the source, such as signal type, frequency, period, duration, ascent and descent times, among others. For now we are only going to keep the DC source that comes by default.

*Fig. 11: Right click on the voltage source to enter the value.*

Resistors

Let’s add the resistor, press the button of the AND gate again (figure 9) and this time we write “resistor” in the search bar. Select the generic resistor shown in figure 12.

*Fig. 12: Add the “resistor” component to the schematic.*

We place it in the workspace and right click on it to enter the parameters.

For now we will only enter a resistance value of 1000 (the standard unit is Ohm, as we see in figure 13 between square brackets to the left of the value 1000).

*Fig. 13: Right click on resistance to enter the values.*

Wiring

When all the elements are in place, let’s make the connections. Click on the pencil button shown in Figure 9 or use the F3 shortcut.

Then we draw the connections between the source and the resistance.

*Fig. 14: Use F3 or the menu buttons to make the connections of the elements.*

Ground

Finally, in order for the program to perform the calculations, it needs a ground point for reference. Click on the triangular button in figure 9 or with the “G” key.

We place the ground on the cable that is connected to the negative terminal of the source, as shown in figure 15.

*Fig. 15: For the schematic to work, a reference ground must be added to the circuit.*

Simulation

When we finish the schematic, we go on to configure the simulation parameters.

If this is the first time we are going to simulate, click on the Run button shown in figure 16. If this is not the first time, go to the “Simulate” tab and click on “Edit Simulation CMD”.

In the Edit Simulation window we are going to choose the last tab called “DC op pnt”, which is shown in figure 17.

*Fig. 17: In the simulation configuration window, select the “DC op pnt” tab and click OK.*

With this option the program will make a direct current calculation of the circuit, showing the voltages in all the nodes and the currents in all the branches.

*Fig. 18: A window appears with the operating values of the DC circuit.*

In the window that appears we can see that the current in the resistance is 5 mA, which is condiced with taking the 5 V of the source and dividing them by 1000 Ohms of the resistance, according to the Law of Ohm.

With this we finish the exercise, we are ready to simulate more complex electrical and electronic circuits. In other articles we will talk about how to draw graphs or produce other simulations.