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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I've never used Splce before, but I want to learn. Maybe I got the wrong one, but I downloaded LTSplice IV from Linear Technologies website. Is this correct? Are they all similar?
I am now trying to put together a basic circuit to play with the program. I have a voltage source, but I'm looking for transformers and bridges. Where would I find them? I don't see them in the basic Draft list.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Ok. I created a simple RC circuit. i want to watch the voltage rise as I'm charging a capacitor. I used the
.trans 0 100ms 0 for my command
i have a resistor in series with a RC pair. However, when I run my DC voltage of 100v the capacitor is charged to 100v instantly. How do I construct the voltage source or command so I can see the exponential charging of the capacitor in LTSpice?
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
A lot of the things you are looking for are general to spice in general, so you should be able to find a fair amount of information online. LTspice is a fine choice, its what I have used in my classes and personal projects.
Transformers are coupled inductors in LTspice and spice in general, you can set the coupling via a spice command, the turn ration is the square root of the turn ratio.
LTspice finds the steady state solution before simulating, this is useful for more complex circuits. However, it means that circuits such as a RC circuit will initialize to the steady state solution where the capacitor voltage is equal to the supply voltage. You can stop this happening by checking the box to "skip initial operating point solution".
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
IamSmooth wrote ...
Ok. I created a simple RC circuit. i want to watch the voltage rise as I'm charging a capacitor. I used the
.trans 0 100ms 0 for my command
i have a resistor in series with a RC pair. However, when I run my DC voltage of 100v the capacitor is charged to 100v instantly. How do I construct the voltage source or command so I can see the exponential charging of the capacitor in LTSpice?
Thanks.
Initial capacitor voltages, and inductor currents for that matter, can be set as initial conditions as a property on that component for when they matter, and can be left for the initial point analysis to set when they don't (like as decoupling in a bias circuit).
I started using SPICE with SIMETRIX. It's a very smooth nice looking front end, which has really spoilt me. Unfortunately the free version is very limited, 150 nodes means 2 opamps are usually too big to simulate, and you can't run scripts. LTSpice OTOH is the full ticket for free, unlimited circuit size and no crippled features, it's a pity it looks so piggin' ugly. Lots of people use it, and I'm switching to it too, because I need the larger circuit size.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I personally use QUCS when I need to do circuit simulation It is basically a direct graphical frontend for the original berkley spice, and generally works well. Also integrates well with octave for more advanced processing, ability to do digital simulations with verilog support, etc; if you are into that kind of thing.
Back when I was getting into the nitty gritty of RF design I used ADS from agilent, and I will admit that it blew the socks off QUCS (part library several orders of magnitude larger, professionally done UI, ability to adjust component values on the fly for some types of simulations, automatic solvers, etc) but for general twiddling of circuits I still go to QUCS because it is lightweight, quick, etc.
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