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IamSmooth

Sun Sept 06 2009, 09:03PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Is there any good freeware program or one for purchase that can be used to simulate circuits on the PC or iMac? Is SPICE the best?

Steve Conner

Sun Sept 06 2009, 09:16PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

LTSpice is probably the best bang for the buck, it's free and works fairly well.

IamSmooth

Sun Sept 06 2009, 10:59PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

I'll look into it. General question: does anyone here use simulation software, and does it really help with your design?

Bjørn

Sun Sept 06 2009, 11:21PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Simulations normally does not simulate any real world circuits but ideal mathematical models so they can be hard to relate to reality. A good oscilloscope and a breadboard can be a lot more efficient.

Since the simulation takes away all the real world complexity it can be useful for understanding how things work and finding out what will affect the circuit without having to struggle with parasitic effects that can make it very hard to figure out what is really going on.

Have a look here:

Carbon_Rod

Sun Sept 06 2009, 11:38PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Depends on what kind of simulations one plans to run.

Protel/Altium-Designer
- about 60% accurate
- Simulations may require initial-condition setup
- most libraries are not for simulation
- Overpriced for Ideal models
- RF/Thermal based routing engine

Proteus

multisim/electronics-workbench:

- about 80% accurate
- some library objects are inaccurate/incomplete
- best value for licensing

Cadence

- pricing is not available for individuals

SolidWorks plug in:

- cables and harnesses

There is other application specific software that may be more appropriate for your needs.

Cheers,

Dr. Slack

Mon Sept 07 2009, 07:40AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Check the HVwiki under "simulation", there are several, my favourite is Simmetrix, but being used to one or groking the GUI is perhaps the most important.

Bear in mind that simulation software at best only answers exactly the question you ask it, and nothing more. You have to provide the circuit topology. If you don't ask it about real world parasitics, it will stay precisely schtum. It needs your imagination and analysis skills to determine which parasitics are irrelevant, so should be left out to avoid over-complicating the model, and which are vital, without which it doesn't work, or doesn't work for long!

For instance, with your 1000uF capacitor loaded IGBT test, unless you had chosen to monitor the capacitor or IGBT current, you wouldn't have notice the device-destroying current spike. You might have noticed that a good model of the IGBT was slow to turn on into this load, but if you had used a voltage controlled current source as a crude IGBT model, then the turn on voltage waveforms might have looked reasonable at a first glance. (When Steve mentioned in another thread that you could bung a capacitor into your load, I rather think he meant somewhere beneficial rather than somewhere detrimental). The capacitor ESR is a parasitic that may or may not be important here.

Simulation software really is the ultimate GIGO, the real world has a lot to recommend it.

One of the joys of simulation is being able to scope exactly what you want to see, differnetial voltages, current flows, small signals without being corrupted by big spikes in adjacent components. One of the dangers of simulation is to allow you to forget that you don't have this luxury in the real world, and your control circuits *will* see those nasty spikes from adjacent components, unless you get the topology right.

tobias

Tue Sept 08 2009, 12:25AM

Registered Member #1956 Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172

Did you tryied Proteus?

It's not cheap, can simulate fairly well but in my opinion the time and effort put in a simulation does not whorth it. You never know if the results are valid, you have to worry about spice models and everything..

But if you wanna try, get a trial license of Proteus. It's the best simulator I've tryed.

Sat Sept 26 2009, 08:09PM

Registered Member #2372 Joined:
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Posts: 62

I disagree with the comments that simulation software doesnt translate to real circuits. As one of replies mentions, it solves the exact math problem that you put into it. If you ignore things like the inductance of the capacitors and wires/transmission lines you are using to deliver the pulse then you are not putting in the correct information into the code so it will be wrong. I have used circuit simulation software predictively lots of times for pulsed power circuits and also circuits containing nonlinear elements. If you are designing a circuit these codes are very useful if you actually incorporate things that are in the real circuit. If you have a capacitor hooked up to 2 foot long wires etc., the inductance of things like this can be calculated mathematically and then put into the code as an inductor, if you dont do it you arent modeling the real circuit.

LTspice is a free code that I have successfully used in a predictive manner for circuit simulation.

doctor electrons

Sat Sept 26 2009, 08:15PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

I use National Instruments Multisim Circuit Design Suite w/Utilliboard. Its expensive, but it does work very well.
I have been using it at work for about 4 years and we rely on it quite a bit for pre-prototyping. Check it out!

IamSmooth

Sun Sept 27 2009, 06:20PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Ok Doc. I loaded LTsplice and have been playing with it. I see there are a lot of Linear Technology chips. What do I do if I want to simulate an Internation Rectifier IRS21844 (half-bridge driver) or a TL494? Do I have to find a similar LT chip?

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