This course explains how to analyze circuits that have direct current (DC) current or voltage sources. A DC source is one that is constant. Circuits with resistors, capacitors, and inductors are covered, both analytically and experimentally. Some practical applications in sensors are demonstrated.
1.5 Intro to Circuit Diagrams
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來自 Georgia Institute of Technology 的課程
Linear Circuits 1: DC Analysis
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從本節課中
Module 1: Introduction
This module reviews background material from physics on the basic properties of electricity and electrical circuits.
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Dr. Bonnie H. FerriProfessor
Electrical and Computer Engineering
Dr. Joyelle HarrisDirector of the Engineering for Social Innovation Center
School of Electrical and Computer Engineering
Dr Mary Ann Weitnauer
[MUSIC]
Welcome to Linear Circuits.
I'm Dr. Harris.
The purpose of this lesson is to introduce you to basic circuit diagrams.
They're important because any time you have to analyze an electronic circuit.
You'll probably receive the diagram for that circuit.
Am I analyze, you should really be able to look at the symbols and
know what they mean.
So by the end of this lesson, you should understand a basic electronic circuit.
This lesson builds upon current, voltage and resistance.
Remember that current describes how electrons flow through a circuit.
Voltage describes how the energy changes over time for those electrons that were
flowing and resistance describes how this circuit opposes the flow of electrons.
Now lets consider a circuit diagram with basic elements.
The first thing I want to point out are the wires.
Two of which are circled here.
Wires are lines that connect circuit elements in the circuit diagram.
In actual life, the wires might be pieces of copper that are connecting
the different elements, but in a circuit they're going to be basically lines.
Wires also have zero resistance and zero voltage drop.
We know that that's not true in life, everything has some internal resistance.
But for the basics of circuit analysis,
we can assume that they have zero resistance and zero voltage drop.
Wires also help to form nodes and
junctions which we'll discuss a bit more later.
Now, the circuit elements that are present in this circuit are first,
an independent voltage source.
We see it has a plus and a minus with a circle around it.
It's an independent voltage source because it's defined by the user.
It might be five volts or ten volts but the voltage source is what
it is regardless of what else is going on in the circuit.
Later on you'll learn about dependent voltage sources that actually depend on
other factors in the circuit.
This circuit also contains an independent current source.
It's an arrow that's pointing in either direction with a circle around it.
Now, please note that even though the plus and the minus are top and
bottom in the independent voltage source and the arrow points up
in the independent current source, these could easily be flipped.
For the current source the arrow could be pointing down.
For the voltage source the plus and
the minus could be rotated such as that the plus is at the bottom.
It just tells you the reference direction for current flow or for the voltage drop.
The other element, another element that's in this circuit, is a resistor.
A line.
A bunch of zigzag lines.
It doesn't matter how many zigzags are there.
That's the symbol for a resistor.
And finally you have a ground.
There are several different types of symbols for ground, but
these are the ones that we'll use throughout this course.
And the ground gives you the reference direction.
We know that voltage always has have a reference direction so
the ground gives you a reference direction for that voltage.
Now consider the difference between a Node and a junction.
A node is any point on the circuit where two or more circuit elements meet.
Also important to know about a node is that nodes are only different
if they have a different voltage.
So remember there's no voltage drop along a wire.
So you have to go through a circuit element in order to have a voltage drop,
and that's the only way you can have a different node.
A junction on the other hand, is the point where wires meet.
So, any given node might have several junctions along the same node.
And this is a very important concept.
So at this point, let's practice.
Looking at this circuit, identify the nodes.
How many nodes do you see?
Also make a note of the junctions.
Now remember that, a node is where different circuit elements meet.
So we have a node here.
And the circuit elements that are meeting are the independent current source,
resistors and the independent voltage source.
We also have a node here.
Again the current source and the resistors.
And we have node here.
So this circuit has three nodes.
And notice that the nodes are different from the junctions.
We have places where the wires meet.
So several junctions.
Which are typically represented by these bumps in the circuit diagram.
These little circles.
But even though we only have multiple junctions, we only have three nodes.
Something else you should know about circuits,
is how to identify a short-circuit.
In life we use that term haphazardly.
We can say if something broke then it probably had a short.
Some electrical short.
But it actually has a very specific meaning.
A wire that has the same start and
end node as another circuit element, shorts that element.
And the reason shorts are important to recognize is because current will always
travel through the short instead of that circuit element that the wire is shorting.
Now, sometimes shorts can be introduced on purpose.
Say you just want to ignore part of your circuit.
You can introduce a short at the same start and end node for
that part of the circuit and current won't travel through that circuit.
However, if you accidentally introduce a short,
then your circuit is not going to behave in the way you want it to.
The opposite of a short is an open circuit.
Opens are also very important to recognize whether you've introduced
them intentionally or unintentionally.
An open circuit has terminals that are not connected to any other circuit element.
And opens are important because no current will flow through an open circuit.
If you introduce an open circuit intentionally,
then perhaps you could use it to measure the voltage drop across an element because
no current is going to be flowing through it, you can measure a voltage drop.
But if you introduce an open circuit unintentionally,
again your circuit is not going to behave as you intended it.
So now take a moment and
look at this circuit to identify the short and the open.
Circle them and then we'll work them together and
identify the short and the open.
Remember that a short has the same starting node and
ending node as another circuit element.
So let's look at the starting node for resistor R4 and
the ending node for resistor R4.
Notice that this line has the same start and end node as R4.
So current is going to flow through this short
instead of through this resistor R4.
Which is fine if you wanted to take R4 out of the circuit.
But if R4 needs to be in the circuit then you have to recognize you
shortened it out.
The open on the other hand, is here.
Across resistor R6.
No current is going to flow because these terminals are not connected.
They're not closed.
Current will only flow through a closed loop.
Now perhaps you want to measure the voltage drop across R6.
And this open would be fine.
You could attach leads to the volt meter to these two terminals, and
that would be fine.
But if this was unintentional, the circuit wouldn't behave in the manner you want it.
The key concepts that we have discussed in this lesson are first,
remember that wires are lines that connect circuit elements.
Wires meet at junctions, but circuit elements meet at nodes.
Always distinguish between a junction and a node.
Current will always flow through a short circuit.
And remember that a short circuit is any wire that has the same start and
end node as another circuit element.
And current will never flow through an open circuit
because current needs a closed circuit in order to flow.
Thanks for your attention.
I'll see you next time.
[MUSIC]
