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LTSpice Tutorial

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56 pointsTomte28 comments

It's extremely useful when used for its intended purpose - designing power supplies using Linear Technology components. Here's a design I did with it.[1] This is a little box for driving antique Teletype machines from a USB port. Those need a current loop running at 60mA constant current, up to 120VDC, driving an electromagnet with a 5H inductance. I wanted to generate that from the USB port's power, which required a moderately exotic switching power supply design.

The LTSpice simulation made it possible to get that right. Especially from a noise control perspective. Switching power supplies generate spikes, and so does turning off that electromagnet with its huge inductance. Those spikes have to be kept out of the USB port or its protection circuitry will shut it down. Spikes need to be suppressed in both the current and voltage dimensions. LTSpice lets you watch the switcher spikes, the electromagnet spikes, and the inrush current. When you add a few surface mount capacitors and ferrite beads in the right places, the spikes can be almost totally suppressed. It just took a few cheap parts. The simulator lets you find values that work.

The SPICE models for Linear Technology components match reality well. That's what LTSpice is really about - a good model library.

[1] https://github.com/John-Nagle/ttyloopdriver/tree/master/circ...

FesZ is one of the best electronics YouTubers. Most of his videos walk you through a topic from theory, to simulation, to build and test. Everything he does is cheap enough that you can follow along yourself for a few bucks, assuming you have some basic equipment.

I haven't come across FesZ before, but from your description I'd add 'Phil's Lab' as a suggestion if that appeals. Fairly new, but similar approach, lots of projects typically completed in a single video, no shying away from theory - quite refreshing having seen every EEVBlog video.

Subscribing due to your comment. Will take a look. Thank you.

I love LTSpice. Its UI has quirks, but it's really been a joy to use.

One gripe I have with the team that built it: it's typically a tool that would immensely benefit from being Open-Sourced.

It would also benefit the company that owns it.

But, it's yet another case the traditional HW guys mentality, a world where everything is IP, everything is secret by default, even when it doesn't earn you a dime.

The most popular FOSS spice simulator is NGSpice: http://ngspice.sourceforge.net/

None of these tools have changed much since the 90's - just like the EDA industry in general

Also see Qucs-S, which is a GUI for ngspice and a few other engines.

https://ra3xdh.github.io/

Oo that looks nice! Qucs had a surprisingly great GUI - you wouldn't believe it was an EDA tool!

There is an interesting 6-part LTSpice overview/training on YouTube by none other than the creator of LTSpice itself (Mike Engelhardt) and at the very start he mentions why he thinks that the best simulators are written by the concerns that need them (e.g. Linear Technology at the time, Analog Devices now) as opposed to software companies. See https://m.youtube.com/watch?v=6gKThjZIj-s.

> the best simulators are written by the concerns that need them

I agree 100% with that statement.

But that statement is also 100% orthogonal to mine (Analog should OpenSource LTSpice: both they and LTSpice users would benefit immensely from doing that)

But it's a hardware company, this is an argument they are culturally incapable of understanding: the whole OpenSource thing is just alien to their way of thinking.

NGspice is open source. IMHO the only improvents in it are new models and some bug fixes. However, the program itself became worse by stripping the help part and by making nutmeg a part of the main program.

I've been getting by for a while using circuitjs[1] to simulate sections of circuits I'm building. I hope to one day bite the bullet and climb the steep learning curve of LTSpice

[1] https://www.falstad.com/circuit/circuitjs.html

the steep learning curve? It's probably the simplest simulator ever built. You can learn it in like an hour and be effective.

I wonder how many years it will be before LTSpice isn't the best option out there for free circuit simulation. It really is horrible to use.

Is this about the GUI? It's a thin wrapper over the command line program. Use the keyboard shortcuts.

I don't see a contender on the horizon.

I hear this criticism a lot. Am I the only one who likes the LTSpice GUI?

Yeah, it's clunky at first, looks straight out of 1995, and you have to break out SPICE directives for features that really ought to have UI wrappers by now. But once you're used to using it and memorize the keyboard shortcuts it's a breeze. I can capture a schematic faster in LTSpice than in any other tool.

To put it another way, it's certainly less intuitive than most software, but it's an order of magnitude more intuitive than, say, Vim.

I also like the interface because it's fast to use the hotkey-mouse combo.

Try putting a ".meas" directive on the schematic and then right-click it. There might be more UI than you think, but it's still not comprehensive.

The best way to make it feel intuitive imo is to try any spice without the GUI.

> more intuitive than, say, Vim.

I assume you mean to a complete newcomer? Where vim really shines in this context is once you've learnt a little bit, and then so much starts coming for free.

I mean, to be fair you're agreeing that it's old, clunky and incomplete and isn't quite as unintuitive as one of the most unintuitive programs in existence.

I think you're both right. It's pretty bad compared to good GUIs, but it's better than all the competition (the free competition at least)! That's just not saying much.

I don't care about the appearance of the GUI. It just doesn't follow conventions. I understand that those were probably established after it was created, but it's very painful to use after any kind of time off it. The keyboard shortcuts suck.

I think it's sort of like how Linux feels unconventional if you're coming from Windows or Mac. It's technically not, but that's a useless fact because it is for you.

Anyone could make an alternate GUI for any spice, but I've never seen it. Unless you count running spice from a PCB tool like kicad, where it's an afterthought.

The hotkeys are at least configurable, btw. And there's an official cheat sheet for the defaults.

https://www.analog.com/en/technical-articles/ltspice-keyboar...

The keyboard shortcuts suck in every Windows program so i would not blame LTSpice for that. It is still ok that it does not have a ribbon and ribbon style shortcuts.

It's not beautiful, but it is very productive. I'm quite happy with the tool and am not really seeking an alternative.

https://www.falstad.com/circuit/circuitjs.html is great for creating quick and simple intuitive simulations, and visualizing the model

Yeah I love falstad and use it all the time to sketch things out but I don’t trust it to be accurate

I don't find it worse than others. It is a bit different but it does its job well. And the GUI, thank god, remained the same. The buttons are a bit small thought.

Back in undergrad, I used LTSpice to simulate and design a single unit of memory, I believe at the nanometer scale. It certainly has its quirks and can be frustrating to use, but I was one of the few people who were actually able to complete the project and get an A. It was actually quite fun.

I have been using Every Circuit for a while. While you cant really simulate particular components (easily) it does allow you to simulate some trivial waveforms for basic circuits.

[1] https://everycircuit.com/app

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