Basic Circuit Analysis Flashcards
To be equivalent, two circuits must:
1) Represent every component & source
2) Have the same number of nodes
3) Each node must be connected to the same branches
Schematic Node is
Where 2 or more elements connect
A Distributed Node is
A single node spread out, with multiple line segments, elbows and dots… but that are all really just a single node… meaning connecting all the schematic elements with perfect conductors means the voltage everywhere on a distributed node is the same.
The number of branches in a circuit =
The number of elements.
A Loop =
Any closed path going through circuit elements.
Loop rules:
1) A Loop can only pass through a node one time
2) it is ok if loops contain other loops
A mesh =
A loop that has no other loops inside it
A ground =
1) Reference point from which all Voltages are measured
2) The return path for electric current back to its source
3) A direct physical connection to Earth
How to avoid getting trapped by schematic puzzles:
1) You can always count on identical branch currents in every equivalent schematic or real circuit.
2) Always think about current flowing in a branch (ie in a component or source) NOT current flowing in a wire
3) Current in wires may or may not exist in an equivalent version of the schematic, or in the real circuit built from either schematic.
Kirchhoff’s current law:
The sum of all currents flowing into a node equals the sum of currents flowing out of the node.
ΣCurrent in = ΣCurrent out
Kirchhoff’s Voltage Law
The sum of all voltages around a loop is zero. Or, the sum of the voltage rise equals the sum of the voltage drops around a loop.
ΣVn = 0
ΣVrise = ΣVdrop
Node Voltage Method steps:
1) Assign Reference Node (ground)
2) Assign node voltage to remaining source connected to the reference node
3) Solve the easy nodes first (the ones with voltage connected to source)
4) Write KCL for each node
5) Solve system of equations
Mesh Current Method steps:
1) Identify the meshes
2) Assign current variable to each mesh using a constant flow direction
3) Solve the easy ones
4) Write KVL equations for each mesh
5) Solve
Loop Current Method steps are needed when…
Either when a circuit is non-linear (i.e. can’t be drawn without crossing lines) or,
It has a current source shared between two meshes
(Or both)
Loop Current Method steps:
Include equations for some non-mesh loops where every loop includes a circuit element that is not part of any other loop. Then solve the same as with the mesh current method.
You don’t need to include every mesh loop, but every element must be represented at least once. And make sure at least one element in each loop is not included in any other group.
