LTSpice

35 Articles

LTSpice Tips And A Long Tutorial

June 7, 2022 by 7 Comments

We always enjoy videos from [FesZ], so when we saw his latest about tips and tricks for LTSpice, we decided to put the 20 minutes in to watch it. But we noticed in the text that he has an entire series of video tutorials about LTSpice and that this is actually episode 30. So there’s plenty to watch.

Like any tips and tricks video, you might know some of them and you may not care about some of them — for example, the first one talks about setting the colors which is a highly personal preference.  But it is a good bet you’ll find something to like in the video.

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Class A Amplifiers, Virtually

March 9, 2022 by 21 Comments

If you didn’t know better, you might think the phrase “class A amplifier” was a marketing term to help sell amplifiers. But it is, of course, actually a technical description of an amplifier that doesn’t distort the input waveform because it doesn’t depend on multiple elements to handle different areas of the input waveform. Want to know more? [FesZ] has a new video covering the basics of class A amplifiers including some great simulations. You can see the video below.

A class A amplifier uses a transistor that is always biased on. It never saturates or switches off. This is good for linearity, but not always the best for efficiency so there are other classes of amplifiers, too. However, for many applications, class A is the most common configuration.

There are a number of trade-offs involved with each type of amplifier and [FesZ] covers them in detail. But the real interesting part is the simulations in Spice. Sure, you can build the circuits and look at everything with a meter or scope, but using Spice is much handier.

There is a second video upcoming. We hope he covers other amplifier types too, as you really do want to understand the differences when you need to design something. If you want more Spice stuff, check out some of our previous posts. If for some reason, you don’t like LTSpice, there’s always Micro-Cap 12.

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Impedance Matching Revisited

January 13, 2022 by 14 Comments

If you are an old hand at RF design, you probably have a good handle on matching impedance. However, if you are just getting started with RF, [FesZ Electronic]’s latest video series on lossless impedance matching is well worth watching.

Matching is important for several reasons. Maximum power transfer occurs when the source and load impedance match. Also, at RF, mismatched impedance can cause reflections which, again, robs you of useful power. The video covers some math and then moves on to LTSpice to simulate a test circuit. But the part you are really waiting for — the practical circuits — is about 15 minutes in. Since the values you need are often oddball, [FesZ] makes his own adjustable inductors and uses a trimmer capacitor to adjust the actual capacitance value.

This is a big topic, but the first video is a great introduction blending theory, simulation, and hands-on. A great way to get started with a very fundamental RF design skill.

We’ve worked on explaining all this before if you want a second take on it. If you want to understand why mismatched impedance leads to less power delivery, we’ve done that, too.

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EMC Tutorial Puts You In The Loop

October 29, 2021 by 2 Comments

A student once asked his lab instructor why his amplifier was oscillating. After looking at it and noting the wild construction, the instructor remarked, “A better question would be why shouldn’t it oscillate?” The truth of it is, our circuits generate noise and especially if they are oscillating anyway. Distortion and nonlinearities generate harmonics and other component imperfections also contribute.

[FesZ Electronics] has a great video series about noise in switching power supplies and the latest talks about the hot loop. If you want to improve the noise performance of your next design, these videos are well worth watching. You can see the hot loop video below.

We really liked the homebrew noise probes. In addition to real-world probing. The video also observes circuit operation under simulation. Even if you don’t care about noise performance, there’s a lot of good information about basic switching power supply design here.

You can see the difference in a PCB that has a small hot loop versus a very small hot loop. Something to think about next time you are laying out a power supply board.

If you want to dive deeper into noise simulation, we have a good read on that for you. Or ditch simulation, and make your own cheap probe with an SDR dongle.

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Phasors In LTSpice

March 17, 2021 by 8 Comments

[Ted] recently demonstrated the analysis of an RL circuit using a piece of paper, Octave, and LTSpice. If you prefer, the Octave code should work fine in MATLAB, as well. If you are looking to get serious about electronic theory this is a reasonably simple case and is a good chance to get a workout with some of the tools.

We like the approach because too often it is easy to just use the computer and not pick up the understanding that you get when working through a problem by hand. You do need to understand complex numbers, but, overall, the math isn’t too hairy.

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Custom Components In LTSpice

March 16, 2021 by 8 Comments

If you enjoy simulating circuits, you’ve probably used LTSpice. The program has a lot of powerful features we tend to not use, including the ability to make custom components that are quite complex. To illustrate how it works, [asa pro] builds a potentiometer component that is not only a good illustration but also a useful component.

The component is, of course, just two resistors. However, using parameters, the component gets two values, a total resistance and a percentage. Then the actual resistance values adjust themselves.

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Make Some Noise Or Simulate It, At Least

November 3, 2020 by 6 Comments

Noise is a fact of life, especially in electronic circuits. But on our paper schematics and just as often our simulations, there is no noise. If you are blinking an LED on a breadboard, you probably don’t care. But if you are working on something meatier, handling electrical noise gracefully is important and simulation can help you. [Ignacio de Mendizábal] has a great piece on simulating EMC filters using LTSpice that can get you started.

There are many ways of classifying noise and [Ignacio] starts with common-mode versus differential noise, where common-mode is noise with current flowing in the same direction without regard to the circuit’s normal operation, and differential noise having currents that flow in the opposite direction of normal current flow.

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