This course introduces students to the basic components of electronics: diodes, transistors, and op amps. It covers the basic operation and some common applications.

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From the course by Georgia Institute of Technology

Introduction to Electronics

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This course introduces students to the basic components of electronics: diodes, transistors, and op amps. It covers the basic operation and some common applications.

From the lesson

Introduction and Review

Learning Objectives: 1. Review syllabus and procedures of this course. 2. Review concepts from linear circuit theory to aid in understanding material covered in this course.

- Dr. Bonnie H. FerriProfessor

Electrical and Computer Engineering - Dr. Robert Allen Robinson, Jr.Academic Professional

School of Electrical and Computer Engineering

Welcome back to electronics.

Â This is Dr. Ferri.

Â This particular lesson, is a review of Kirchhoff's laws.

Â In a previous lesson, we reviewed, linear circuit components such as resistors and

Â capacitors, and conductors.

Â In this one, we're going to, go through more detail of Kirchoff's Current Law, or

Â KCL, Kirchoff's Voltage Law (KVL).

Â Kirchoff's Voltage Law (KVL) states

Â that the sum of voltages around any closed loop is zero.

Â Now we show an example of a closed loop here.

Â And in order to ply, apply this, we would have to know what these, these voltage is.

Â So, suppose this is, V sub D.

Â V sub A.

Â V sub G.

Â And these are all measured in, volts and this is V sub H.

Â So, I want to do, I, I sum up the voltages around here.

Â Now, if I'm summing the voltage from this point, to this point, so I'm looking at

Â the voltage potential, I actually gain voltage, from this point to this point.

Â But, when I do a voltage Kirchhoff's Voltage Law.

Â I want to make sure that I'm always consistent with,

Â the way I use the polarities.

Â So I use a little trick in doing this.

Â I use a trick and say, if I'm going to be summing in this direction,

Â if I come to plus sign first I add it.

Â If I come to plus sign here first I add it.

Â In all these cases I've come to a plus sign first,

Â if I go around in this direction.

Â So I'm going to add these on.

Â If I were to come to, a minus sign first, I would subtract it.

Â That's just, my trick in making sure I get the polarity right.

Â So starting at this point, I would have V sub H plus V sub D plus V sub A.

Â Plus V sub G, all have to sum to zero.

Â And that's going to be true of any loop.

Â It'll be true of this loop.

Â It'll be true of this loop.

Â Any loop, any closed loop.

Â Now, I'm going to have you do a KVL quiz here.

Â So, looking at this circuit, I want you to find VH.

Â Now, coming back to the solution here.

Â Find VH I want to do a KVL.

Â Well, I can do a KVL around this loop, but I don't know what this voltage drop is.

Â So let me do a KVL around this loop right here.

Â And the way I do a KVL is,

Â in the direction I go, if I hit a plus sign first, I add it.

Â If I hit a minus sign here as in this case I would subtract it.

Â Now it's not strictly physical,

Â because actually I'm losing potential as I go from here to here.

Â But it's just a trick that I use to keep my polarities, correct.

Â So, going around here starting with, plus VH and then I get to the minus two.

Â Over here I get a plus, minus one and around here I get

Â a minus 5 and then plus 4 equals 0.

Â So, when I add these up.

Â Let's say I'm going to have a, a minus 8 plus 4.

Â In other words solving for it I get a, 4 volts.

Â Now let's look at KVL and Parallel circuits.

Â So I got.

Â These two elements, that are parallel to one another and

Â that's the only thing in this circuit.

Â So, if I do a KVL around here, and this is V sub A, and this is V sub B,

Â going around here, I would have, in this direction, V sub A.

Â Minus V sub B, because I hit that minus sign first, is equal to 0.

Â In other words, V sub A is equal to V sub B.

Â And that is true, any time we've

Â got two elements, that are in parallel with one another, they're going to have

Â the same voltage drop, as long as you've defined them with the same polarity.

Â So any two elements that are parallel with one another,

Â have the same voltage across them.

Â Now this a, a numerical example,

Â an actual circuit example with resisters in there of a caveat.

Â And I'd like to be able to, solve this.

Â And do for example a Kirchoff's Voltage Law across this.

Â So let me, let me write this.

Â There's lots of, loops I could do.

Â And do this loop right here.

Â I can do this loop up here.

Â So let me write Kirchoff's Voltage Law around here.

Â So I would like to be able to, write, so I'm going to do it around here.

Â I'll need to be able to, mention or, or write an expression for

Â the voltage drop across this resistor.

Â Now, by the convention we show that resistance goes into

Â the plus side in order for us to be able to use Ohm's Law.

Â So we'll call that V sub one.

Â So, if I want to go around here I hit the minus sign first, minus 10.

Â Plus this voltage drop here, V sub 1, plus V 0.

Â And, that's all I've got on this loop is equal to 0.

Â So V sub 1 is equal to i sub 1 times 20.

Â V sub zero is equal to i sub 2 times 10.

Â And this is by Ohm's Law.

Â So now I got an expression.

Â That I can use to solve for, for these variable here in terms of the currents.

Â I can also do a loop around this way.

Â Suppose, I do this loop around here so in this case I hit the plus sign first.

Â So it's plus 2, minus v 0 'cause I hit that minus sign and

Â then plus voltage drop.

Â Well remember the current goes into the plus side.

Â Plus I 3 5 is equal to zero.

Â So I have another expression and v zero again.

Â Is equal to i2 times 10.

Â So what we've been showing here is how to write KVL's for a particular circuit,

Â an actual circuit, that we're making use of Ohm's Law for that.

Â Kirchhoff's Current Law says that the current entering a node equals the current

Â leaving a node.

Â For example, suppose I've got this current.

Â This is a node right here and this is a node because everything here is connected.

Â So this is a node there and call this of A and this I'll call

Â of B, of E, and.

Â I sub d.

Â So, if I do KCL at this node I would sum up everything entering and that would be

Â i sub b plus i sub d is equal to the sum of what's leaving, i sub a plus i sub e.

Â And that's true for any node.

Â So, I 've got a node over here.

Â And in note over here and note over here.

Â It's true at every note.

Â So in this particular case we look at for

Â example if we draw the current if I've changed the directions so

Â now this one I'm showing this way this way this way now it's entry is word i sub A.

Â Plus I sub B, what's leaving is I sub D plus I sub E.

Â So if I change the arrow, the reference of my current,

Â I have to just be careful that I'm consistent with it.

Â Now, if I have two elements in series with one another, then all the current-

Â this is a node between them-

Â the current entering has to equal the current leaving.

Â So, if this is i sub A, and this is i sub B, then the current

Â that enters this node, i sub A, has to equal the current that leaves this node.

Â So that means that any current that flows through an elements that are in

Â series with one another, is the same current.

Â So, this current is all the same because they're in series.

Â Let's look at a KCL for a particular numerical example a,

Â a circuit, real circuit.

Â And I'm going to look at this node right here.

Â And I want to look at all the currents entering and leaving.

Â And let me define this as being.

Â The one that maybe I'm trying to solve for i.

Â So, let me look at the currents entering.

Â We have i1 is equal to i3 plus i2 plus i.

Â And that's, that's just how to do the KCL at this node.

Â In summary, we've introduced the Kirchhoff's voltage line,

Â Kirchhoff's current law.

Â We've applied them, the Kirchhoff's voltage law to parallel elements and

Â found that two elements in parallel have the same voltage across them.

Â We've applied the KCL to series elements and saw that any two elements that were in

Â series had the same current going through them.

Â And then we also solved a simple circuit using Kirchhoff's laws.

Â In our next lesson we'll do a review of impedance methods.

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