4 Thevenin

Now that we know how to calculate the Thebonon equivalent circuit, it's very easy to get the Norton

from source transformation. The Norton equivalent current is going

to be V Thevenin divided by R Thebonin, and the parallel resistor here will be

equal to the series resistor in Febonin. Now let's talk about power transfer.

When we have our active circuit, which we can model with a Febonin

equivalent circuit, and our passive circuit, which was modeled just as a load,

we might very often want to be able to maximize the power that gets to the load.

Imagine what would happen if we increase this resistance.

We can see that by increasing the resistance because we've got a voltage divider here,

we get the larger possible voltage, but we get a much smaller current

because from Ohm's law that says we have a higher resistance. What if I made the load very small?

In that case I have a large current but a small voltage. So in fact,

where's the maximum power transfer? If you calculate the current and you calculate the voltage,

you'll come up with this equation right here. And if we plot that,

we'll see that the maximum value happens when the load is equal to the source.

So our maximum power transfer happens when Rs and RL are matched. You often say matched,

and this is the maximum power that can be delivered to that load.

Now here's our electrical engineering circuit analysis toolbox with the addition

of Thevenin and Norton included. Now, Febin and Norton are very important because

they allow us to simplify our circuit. They're somewhat like the resistors and

series and parallel law that allows us to simplify or the superposition. So let's say that this is

a simplification method, this is a simplification method, and this is a simplification method.

The other methods can all be used in this Norton and Febin equivalent circuit.

In fact, you saw us use the node voltage and this equation right here.

Ohm's law can also be used voltage dividers and current dividers,

all for doing the analysis that gives us the feminine and Norton equivalent circuits.

So what did we do today? We talked about how to analyze systems of circuits that might be

more complicated by breaking them down into simple blocks using the

concept of input and output resistance. We know that if the output resistance

is much smaller than the input resistance of the next block that we can

analyze these individually and if not, we can expect to see voltage loading.

We analyzed how to calculate feminine

equivalent circuits by open circuiting

the points A to B and measuring or simulating or calculating B feminine.

And then we talked about three different methods of being able to measure our Thevenin.

We know that we could convert this to a Norton equivalent circuit using source transformation.

And then we talked about maximum power transfer, which is where the block that has this

input resistance rather the output resistance is connected to the load

and these two have to be matched or equal for maximum power transfer. Finally,

we talked about the updated EC analysis toolbox where we now know that we

can use Thevenin and Norton as one of our simplification tools and we

can apply any of the other circuit analysis tools to do our calculation.

So thanks very much for joining me for the discussion of Thevenin and Norton equivalent circuits.