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Hello, everyone.
In this lecture we will review the basic contents in this semester.
First the content of the 45 lectures can be divided into three categories.
We have four things in the first category.
The first thing is the definition of the variables,
wherein the voltage and current are called as branch quantities.
After defined reference directions of voltage and current,
there are two conditions of so-called associative and non-associative.
The power has different definitions for associative and non-associative.
We had special discussions about it in lectures 3 and 5.
In addition, after defined reference directions of voltage and current,
we learned KCL and KVL.
We called them topological constraints of circuits
which is discussed in lecture 10.
In addition to the topological constraints,
we also introduced a lot of basic circuit components
such as resistors, sources
(including independent sources and dependent sources),
operational amplifiers, and MOSFET.
Resistors were introduced in the 6th lecture.
Independent sources and dependent sources
are introduced in lecture 7 and lecture 9 respectively.
The fourth part is the special content,
in which we discussed the two-port network.
In the section of linear resistive circuits analysis,
we first introduced several kinds of equivalent transformations.
This is the practical skill for solving problems.
In addition we introduced four kinds of very important tools for solving circuits.
In the nonlinear resistance circuits,
we introduced four analysis methods.
Let's review some key parts.
Before review specific contents,
we need to classify contents of the 45 lectures in this semester.
Look, we have such a flash in the Syllabus part of the course.
It divides the contents of the 45 lectures
into four categories: concepts, models, solving methods, and applications.
We put the title and serial number of each lecture here.
The flash have a very important application.
For example, if you want to know the prerequisites of KCL and KVL in lecture 10,
you only need to click 10 in the flash.
Did you find?
You just need to learn lectures 1, 2, 3, and 4
and then you can learn lecture 10 directly.
Again for instance,
If you want to learn the basic knowledge about logic gate circuit,
you click 25,
you'll find that you need only to learn lectures 1-10, 15, 18-23
and 24, then you can complete control the content of lecture 25.
According to the flash,
you can fully realize our so-called "Demand-based Learning".
The flash is a very effective tool.
I hope you can properly use it.
Next, let’s review a few key contents.
The first is the operational amplifiers.
In contents of this semester,
we mainly discussed ideal operational amplifiers.
The ideal operational amplifiers have three basic characteristics,
the first is that A tends to infinity,
the second is that Ri tends to infinity,
The third is that Ro tends to zero.
Secondly all circuits we discussed are negative feedback circuits.
That is to say, through a element connects to the output end,
the signal feed back to the inverting input end.
Thirdly, when we analyze the ideal operational amplifiers containing negative feedback,
if we are sure that it works in the linear circuit region,
we have the so-called the virtual short method and the virtual open method.
The so-called virtual short refers to the voltage between the inverting input and non-inverting input of the operational amplifier tends to zero,
which is similar to the short circuit.
That is the potentials of the two nodes are the same.
But in fact they are not short circuit.
So it is called virtual short.
The so-called virtual open
refers to that the current flowing into the inverting input and the non-inverting input of the operational amplifier tend to zero
because of the large input resistance of the operational amplifier.
It looks like a open circuit (but not real open).
By using the virtual short method and virtual open method,
we can analyze conveniently
the ideal operational amplifier circuits with negative feedback.
What I want to emphasize is that
here the negative feedback ideal operational amplifier circuit
is assumed to work in the linear section.
About the operational amplifier, we introduced it in lectures 18 and 21.
You can review it carefully.
About MOSFETs,
we discussed three working sections.
They are open circuit between D and S,
a resistance between D and S,
a non-linear voltage controlled current source between D and S.
We've introduced voltage controlled current sources and voltage controlled resistors in lecture 9.
In lectures from 24 to 26,
we discussed gate circuits constituted by this resistors.
We discussed amplifiers constituted by the voltage controlled current sources in lecture 45.
There are many definitions for the two-port.
First of all, we gave four kinds of definitions for the two-port.
Their parameter equations
need to be remembered.
We also discussed the reciprocal two-port and symmetric two-port.
The four parameters
have different conditions on the reciprocal two-port and symmetric two-port.
This also need to be remembered.
In addition,
For parameters G, R and T,
after gave the parameters,
sometimes we need to provide their equivalent circuits,
Different two-ports can be connected in cascade, in series and in parallel.
The discussion about the two-port
are in lectures from 27 to 31.
You can review carefully.
Equivalent transformations are very important tools for solving circuits.
in this semester,
we have introduced three kinds of equivalent transformations.
The first is about the input resistance.
Here we recommend the order as follows.
Series and parallel connection first,
then the balanced bridge,
and the Y-delta transformation.
If it contains dependent sources,
we recommend that you use the u->i method or i->u method.
The equivalent transformations of resistors
have been discussed in lectures from 12 to 15.
The equivalent transformation of sources is also very important.
One of the most important is the transformation equation of real voltage sources and real current sources.
In addition to the equivalent transformation of sources,
the conclusion of the maximum power transfer can be used directly.
When Rl=Ri,
it obtains the maximum power, i.e. [(Us)^2]/(4*Ri).
The next are two basic methods of standardization circuit analysis.
There are the node voltage method and the loop current method respectively.
The node voltage method is to use node voltages as variables
and write KCL equations of independent nodes.
The loop current method is to use loop currents as variables
and write the KVL equation of each loop.
It should be noted for the node method,
if there is only one independent voltage source between two nodes,
we need to have some special techniques.
Other special cases, for example
branches contain dependent sources,
were discussed in detail in lecture 33.
For the loop current method,
if the branch contains independent current source
or dependent sources,
we have discussed the techniques in lecture 34.
We have introduced several circuit analysis theorems in this semester.
The superposition theorem and the Thevenin theorem are most important.
About the superposition theorem, it needs to explain first that
it is an important theorem of linear circuits.
Secondly when solving circuits contain two or more independent sources,
you can consider using it.
Dependent sources are not to participate in the superposition.
The Thevenin theorem has very wide applications.
When solving the maximum power transmission or the voltage or current of one branch,
we can consider using the Thevenin theorem.
There is a very important technique about the Thevenin theorem,
i.e. how to select the equivalent port and find its corresponding Thevenin equivalent circuit.
You need to summarize it in the process of doing exercises.
As to solving open circuit voltage, short circuit current,
or input resistance, we only need to use some equivalent analysis techniques introduced before.
Or KCL and KVL
are enough.
About theorems, we have discussed in detail in lectures 35-36.
The last part is about the analysis of nonlinear resistive circuits.
We introduced four analysis methods. 163 00:10:00,545 --> 00:10:01,846 The analytical method has
the advantage that it may be able to provide expressions for the nonlinear circuits.
But the problem is that
it is difficult to write equations,
and it need numerical methods for solving equations.
the graphical method's physical concept is very clear.
But the solution precision of the graphic method is not high.
The precision of the piecewise linear method depends on the number of segments.
In order to find out which linear section the real component really works in,
we often need to use the suppose-verify method.
The small signal method is used to analyze
nonlinear resistive circuits with small disturbance.
Or to realize some functional circuits for special purpose
for instance, the method is common used in the analysis of amplifiers.
We have analyzed the nonlinear resistance circuits in detail in lectures 40-44.
In this 8 weeks course,
We learned together
the linear and nonlinear resistance circuits, many important concepts and analysis methods.
"Principles of Electric Circuits" teaching group of Tsinghua university
express our heartfelt thanks for your active participation.
From February 24, 2014,
we will start the second part of "Principles of Electric Circuits" course.
Welcome you taking the course.