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Where to find help for LTspice/SwitcherCAD

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DSGarcia

New Member
Is there a forum for help with LTspice/SwitcherCAD other than the one on Yahoo Groups? I would rather not give out personal information to Yahoo just to create an account--just trying to limit my exposure.

Just wanting to know how to simulate switches that I can change state during simulation. For example, I would like to change input logic states to then follow what happens.

A beginners tutorial would also be helpful.

Thanks,
Dale
 

Roff

Well-Known Member
DSGarcia said:
Is there a forum for help with LTspice/SwitcherCAD other than the one on Yahoo Groups? I would rather not give out personal information to Yahoo just to create an account--just trying to limit my exposure.

Just wanting to know how to simulate switches that I can change state during simulation. For example, I would like to change input logic states to then follow what happens.

A beginners tutorial would also be helpful.

Thanks,
Dale
That's the only forum I know of. I've never had a privacy issue with them.
If you want to simulate switches, it's pretty easy. You use the SW element, and you will need to create a model for it. You then control the switch with a voltage source.
If you can't figure it out from the Help file, post what you want to do here and we'll see if we can help.
 

DSGarcia

New Member
Ron,
Thanks. I will be traveling in a couple of days and can catch up on the reading on the plane.
Thanks,
Dale
 

Sceadwian

Banned
The Yahoo group really has some resources for LTSpice that I've never found anywhere else. From obscure models to schematics that describe real world complex systems.
 

Papabravo

Well-Known Member
DSGarcia said:
Is there a forum for help with LTspice/SwitcherCAD other than the one on Yahoo Groups? I would rather not give out personal information to Yahoo just to create an account--just trying to limit my exposure.

Just wanting to know how to simulate switches that I can change state during simulation. For example, I would like to change input logic states to then follow what happens.

A beginners tutorial would also be helpful.

Thanks,
Dale
What personal information? You can create multiple ficticious and and completely bogus identities. As a side benfit you get an email address you can use as a spam collector.
 

DSGarcia

New Member
PapaBravo,
Thanks for the suggestion, but the Yahoo terms of service require truthful responses and a honest representation of myself including disclosing my correct birthdate. I know that others may do as you suggest, but my personal values require that I be honest and not perjure myself even though no one else would know. Yes, I agree, it would be nice to have a spam collector, and perhaps when I get really, really stuck with a SCAD problem, I will cave in and get a Yahoo account, but I will honestly agree to and follow their terms of service.
Thanks,
Dale
 

Andy1845c

Active Member
On the topic of SPICE, is it possibly for someone thats not a EE to get anything out of LTspice/SwitcherCAD? Is it of any use to a novice, other then drawing scmatics?

I can't make it do anything. I have no idea what I am doing with it or even what exactly its helpful for. Are there books/websites that break it down a little more then the help file does?
 

Roff

Well-Known Member
Andy1845c said:
On the topic of SPICE, is it possibly for someone thats not a EE to get anything out of LTspice/SwitcherCAD? Is it of any use to a novice, other then drawing scmatics?

I can't make it do anything. I have no idea what I am doing with it or even what exactly its helpful for. Are there books/websites that break it down a little more then the help file does?
If you don't really understand electronics, a simulator will probably be almost worthless. If you don't know approximately what results to expect from a simulation, you have no way of knowing whether you've made an error in setting up your schematic or simulation.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I'm a big anti-simulator fan! - electronics is about wires and components, NOT playing a computer game!. A simulator isn't the real world, and doesn't work like the real world does - they obviously have their uses, but you often have to modify the circuit to make it simulate correctly - whereas the original circuit would work perfectly.
 

DSGarcia

New Member
Nigel Goodwin said:
I'm a big anti-simulator fan! - electronics is about wires and components, NOT playing a computer game!. A simulator isn't the real world, and doesn't work like the real world does - they obviously have their uses, but you often have to modify the circuit to make it simulate correctly - whereas the original circuit would work perfectly.

Nigel, I can't speak for the others, but my thoughts were to substitute various components in a circuit to see how it affects the timing, etc. I am more of a software person and nuts & bolts hardware. I do not do a lot of electronic design and so I don't have a large assortment of parts to play with and do not wish to stock up when I can simulate the circuit to narrow down the parts selection to purchase to use for the prototype. But, as you said, I will get to actual wires and components for prototype testing.

As a side note, I worked on a project many, many years ago for an automated test company. They developed massive test programs for flight avionics for military aircraft and such. Because the equipment to be tested was very expensive and had very limited availability (as well as security issues), we simulated the avionics electronics to support the development of the test programs. My job was to develop the software to simulate the test instruments on the IEEE-488 bus (HPIB) and respond to the test program host computer as if my side were the actual test equipment operating on the device under test (DUT). I set/retrieved test point values from a Spice simulation of the DUT.
Thanks,
Dale
 

Papabravo

Well-Known Member
Andy1845c said:
On the topic of SPICE, is it possibly for someone thats not a EE to get anything out of LTspice/SwitcherCAD? Is it of any use to a novice, other then drawing scmatics?

I can't make it do anything. I have no idea what I am doing with it or even what exactly its helpful for. Are there books/websites that break it down a little more then the help file does?
Probably the most useful feature of LTSPICE is the ability to input voltage and current requirements for a switching regulator and have a reference design pop up that you can simulate. The design comes complete with component specificatations. Ultimately you still need to understand what is going on, but it sure saves a boatload of time searching through datasheets. The catch? It only does this for LT parts.

Second if you have a potential design, it is much easier to evaluate alternatives. Confirming the operation on a breadboard or PC board is of course still essential. I never shun the use of an available tool, especially a free one, unlike some of the Luddites stuck in the last century.
 

philba

New Member
I'm a fan of simulators. They are an embodiment of the idealized model you get when reading textbooks. In that sense, they are a fantastic learning tool. I use LTSpice all the time to understand some aspect of circuit design that I am unclear on. I can vary parameters and see what happens. I can test out basic assumptions before letting the smoke out of real component.

To be sure, there are lots places where the models are insufficient. For example, anywhere that noise is needed for correct operation of a circuit like some oscillators.

I do agree, however, that you must apply voltage to components to truly understand the realities.

On the subject of yahoo accounts, I think you are being a little overly concerned about "honesty". I have probably 10 yahoo accounts for various purposes. None are nefarious. I am a totally honest guy and sleep very well at night. For privacy, you can opt to keep most of the info from public view when you join groups. No one says you can't sign up your dog or pet goldfish... For animals, I assume age in animal years. The one thing I do is use a different zip code. Given that they don't say it is for your residence, it's not in the slightest bit in violation of their TOS. Note that you should hide your zip code because data miners use that to link your records to other databases. There may be millions of bob smiths in the world but probably not many in your zip code. less common names will hit 100% unique.
 

Roff

Well-Known Member
Nigel Goodwin said:
I'm a big anti-simulator fan! - electronics is about wires and components, NOT playing a computer game!. A simulator isn't the real world, and doesn't work like the real world does - they obviously have their uses, but you often have to modify the circuit to make it simulate correctly - whereas the original circuit would work perfectly.
A simulator isn't a game, it's a tool. Hammers are incredibly handy, but you can definitely smash the crap out of your thumb with one.
I do agree with you to some extent, but I also have to point out that I have designed and simulated, but not built and tested, a lot of circuits for some of the members here and on other forums. I have been thanked many times for providing working solutions this way. The simulator obviously does not design the circuit - I do. But the simulator saves a huge amount of time, and gives me access to virtual hardware that I otherwise would not bother to test.
When I design something for myself, I build it and test it, but, unless it's very simple, I simulate it first.
A few months ago, I was wondering what audio sounded like after passing through a (very simple) sigma-delta A/D and then back to analog (the D/A is just a lowpass filter). I downloaded some WAV files and used them as inputs to a simple sigma-delta A/D in SwitcherCAD III, converted the output of the filter back to a WAV file, and listened to before and after on my computer.
It may not have been a totally realistic simulation, but it allowed me to play with 1st and 2nd order S-D conversion, and the sample rate, and the lowpass filter, without having to obtain or assemble the hardware. It also sounded good enough that I will probably build it at some time.
As you said, Nigel, simulators have their uses.
As I implied in my previous post, garbage in=garbage out.
 
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Andy1845c

Active Member
Ron H said:
If you don't really understand electronics, a simulator will probably be almost worthless. If you don't know approximately what results to expect from a simulation, you have no way of knowing whether you've made an error in setting up your schematic or simulation.

Thanks Ron. I feel better now:D I have LTspice and as much as I try, nothing makes much sense to me. I'd like to just be able to stand over someones shoulder while they ran a circuit in spice so I could see exactly how a circuit sim is used. The whole concept kinda confuses me:eek:
 

Sceadwian

Banned
Nigel,
Without simulators every mass produced electronic device in the world would cease to exist.. Anything with an IC in it at least. IC manufacturers use Spice heavily to test out new designs using very carefully chosen parasitics to represent how a real world design would react. If it weren't for simulators they'd have to etch a new design after every change and probe the IC itself, on modern processors that's prohibitivly difficult and expensive, if not downright impposibble due to the incredbly small feature scale they work with now.
For the hobbyist it's extremely useful for experimentation when you don't know what you're doing as you can just connect any two wires you want and not worry about something blowing up. It might seem alien to anyone that learned the old school way by just using wires and components and failure to teach, but once you understand the concepts behind the circuit you're simulating and can approximate an understanding of it, building the real circuit is significantly easier. Once the initial prototype is built and tested you can compare the simulated data against the real world data you obtain from testing it and figure out where the differences come from, and if you need to do more simulation later you can adjust the simulation parameters to correspond to the real world results. The main problem with simulators is they don't simulate real world parasitics very well. Such as the dielectric absorption of an electrolytic, or the inductance of a capacitor, electron flow noise, p/n junction noise, basically any noise at all, though approximation of noise sources can be inserted if it's truly critical.

And Andy, if you're having that much trouble figuring out how ltspice works load up the examples.... There are 65 Educational examples in the examples directory. Everything from ideal transformers, oscillators, opamps, pll's, switches, varistors, oscilators.. and plenty more. More than enough for someone that's determined to learn from. There are plenty of spice netlists on the net as well but that's a little intimidating because those are just text files. Dive in, when you get in over your head take a break and digest, then just go back to it again. The help files also contain an abundant amount of informations on the various components and even on the more generic spice description language that lets you create your own custom models from ideal components.
 
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