Complex Circuit Analysis

Discussion in 'General Electronics Chat' started by khanjan90, Mar 5, 2010.

  1. khanjan90

    khanjan90 Thread Starter New Member

    Mar 5, 2010

    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. kkazem

    kkazem Active Member

    Jul 23, 2009
    Irvine, CA
    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 power-of-ten letter; the 2nd line could also have been written as: C1 1 0 1u or as
    C1 1 0 1E-6. 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.

    Kamran Kazem
  3. russ_hensel

    russ_hensel Well-Known Member

    Jan 11, 2009
    South Dartmouth Ma
    The general method of doing this is with graph theory and linear algebra. Google may help.
Similar Threads
Forum Title Date
General Electronics Chat The Formula for the Equivalent Resistance of Complex Resistance Network (Circuits)) Apr 11, 2015
General Electronics Chat Reduce a complex resistors circuit Apr 9, 2014
General Electronics Chat Reading more complex circuit schematics Nov 14, 2011
General Electronics Chat please help me, these complex, complicated circuits Jul 29, 2011
General Electronics Chat identifying connections for complex circuits Jan 18, 2011

Share This Page