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#1




Complex Circuit Analysis
Hi,
I'm working on a side project called a 'random circuit analyzer'. Essentially, with given information about randomly laid out conducting pieces (same material) across an area, I want to calculate the resistance from one end to the other (if there are any open paths). The resistance of each piece varies with its length (its 1D). I've taken a courses in electromagnetism, so I'm aware of the Kirchoff's Laws and basic circuit analysis. Before I start working on an algorithm, I was wondering if you guys do know any mathematical ways of analyzing complex circuits. There is only one power supply, and then there is a complex circuit (just many different paths). I was thinking of Fourier Series, but google didn't help much on the issue, so I thought I'd ask the experts. You do not need to explain it computationally, just an explanation on how you would break down a complex circuit to find the resistance across it would be great. Let me know if you need anymore information. Thanks a lot in advance! 
#2




Complex Circuit Computation
Hi,
Fortunately, this is a simple one, if I'm understanding you correctly. No matter how many parallel resistors you have, the total resistance is: Rtotal=1/[(1/R1)+(1/R2)+...+(1/Rn)], for a quantity of n resistors in parallel. That's what it sounds like you have. If you need the current, you can simply compute as follows: Itotal=(Vpwrsupply/Rtotal). I hope that helps. Your question was a bit cryptic and it sounded like you had a large number of parallel resistance paths. If it's more complicated than that, you can use KVL or KCL (Kirchoff's Voltage or Current laws) also known as Loop & Mesh analysis. Even though you said you were familiar with it, I'll say a bit about it for your benefit and for those who may not be familiar with it. No matter how complex or large a circuit is, it can be broken down into a series of sequential loops (for voltage analysis) or a series of nodes for current analysis. What you wind up with in either case is a series of simultaneous equations, which can be solved by a variety of means, such as reduction of variables (I can't remember the more common name), and most importantly, matrix analysis, which lends itself to solution by a computer algorithm. This is precisely how SPICE, PSPICE, HSPICE, etc, all work. The user inputs either a manual netlist after numbering each node, with node 0 always being the ground (return) node. For example, a simple parallel RC circuit might have a SPICE netlist as follows: R1 1 0 1K C1 1 0 1uF where the R1, C1 is the component reference designator, the 1 0 means it connects from node 1 to node 0, and the 1K for the resistor means 1 KOHM. Actually, it doesn't matter what you put after the poweroften letter; the 2nd line could also have been written as: C1 1 0 1u or as C1 1 0 1E6. Obviously, most circuits would be more complex than this, but it serves as an example. SPICE then has an algorithm that turns the netlist into a set of simultaneous equations in matrix form, based on rules of KVL and/or KCL. More modern SPICE programs can allow the user to either input a manual netlist as above, or to draw a schematic using a schematic capture program that outputs the SPICE format netlist. Good luck and I hope this helps. Regards, Kamran Kazem
__________________
Kamran Kazem, Senior Member of IEEE with 30+ years of power electronics, & general analog, digital, & microprosessor design. BSEE & MBA from UC, Irvine kkazem 
#3




The general method of doing this is with graph theory and linear algebra. Google may help.

Tags 
analysis, circuit, complex 
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