 Hey everybody, Chad here from the Electric Academy. Funny story, I just recorded this whole video when I realized that my mic, this part here, you see that? That wasn't plugged in fully into the camera, so there was this horrendous hiss when I went to edit it. And so you can thank me later, or you can thank me now, but it was brutal, so I had the whole thing done. So the way I like it is, it's just a great dry run through. This is gonna be a fantastic video. Today what we're gonna be doing is we're gonna be talking about the Darlington Pear Transistor. Let me just get this mic out of the way. I have been getting a lot of questions about the Darlington Pear, so I thought, what better time to do it than now? So if you don't know anything about transistors, totally okay, hit the I up above there, and it's gonna take you to a playlist full of electronics. In that playlist is about three or four videos on how transistors work, kind of the magic behind them all. But if you don't have time for that, you can follow along here, and I can guarantee that by the end of this, you'll have an understanding of how transistors work. Now, transistors have two functions. Number one, they are used for switching. We're not gonna go into switching circuits in this video. Actually next week, we'll carry on with the whole mini mini series thing. Next week, I'll do one on the alarm circuit that uses two transistors and uses them as switches. But this week, what we're gonna do is we're gonna focus on the second function, which is amplification. Now what I mean by that is, if you have one side of a transistor, and say on that one side, you have one milliamp, you can take that transistor and it can actually amplify that one milliamp or that signal and it's got what's called a beta or an amplification factor, whatever you wanna call it, this magical thing that suddenly takes this one milliamp and turns it into 100 milliamps. Now, I use that term magical jokingly. At its basic, it's not magically turning one milliamp into 100 milliamps. What it is doing is it's taking one milliamp and it's using it to control the 100 milliamps. So we're using a smaller current to control a larger current. And then sometimes we can get in the whole discussion as to whether or not transistors are current based or they're voltage based. If you wanna get into that discussion, let's do that down in the discussion. I would actually love to hear your comments on that. But for this, for our purposes today, we're gonna talk mostly about it being current based. And again, we're also gonna follow electron current flow and not conventional current flow. Again, that's a whole other discussion down for the comments below. Let's jump into the whiteboard and we'll take a look around and see what we're talking about. So here we go. I've got my basic circuit here. This is a Darlington pair transistor circuit. I have my voltage source. So VCC, which is your voltage control circuit. We have our RC, which is our collector resistor, which is basically our load. Then over here, we have our RB, which is our base resistor. So that's kind of what controls all this other current that we're gonna kind of see how this whole sequence works out. Now again, just follow along and the joy of being on YouTube is you can hit pause, you can rewind and go back and do it again. But trust me when I say that these things can actually be quite fun and just take your time with them. You don't need to rush into it. And if you want, I can actually send you, I've got a great worksheet on this to practice with. So I'll try to put a link for that in the description. Remind me if it's not there, make a comment down below if I don't put it in there. I will get it to you because it's just a great way to practice. Now, let's go back to the whiteboard here. So what we have here is Q1, Q2. Those are two transistors. A transistor will have a base side. It will have a collector side and it will have a emitter side. So that's stuff that you're gonna learn if you go back to those videos or maybe you already know. Now in a typical transistor circuit, we have a forward voltage drop from our base to our emitter of 0.7 volts because they're basically transistors act like back-to-back diodes and a silicon diode has a 0.7 volt drop when it's in forward bias. So base to emitter here is gonna be that 0.7 volt drop. Now on a typical transistor circuit, we need to take that into account for RB. However, stop. We need to take a look and we see that we've got a 0.7 volt drop on this Q1. We also have a 0.7 volt drop on Q2 because it's a silicon resistor as well. Which means that these two volt drops are in series. You can kind of see what I'm talking about here. I'm series-ess. I got 0.7 to 0.7, which means I have a 1.4 volt drop. We don't have a 0.7 volt drop anymore because we have two transistors in series with each other. So instead of taking your RB here, your VRB, typically what we would do is take your VCC minus 0.7 to get VRB. Now we're taking VCC minus 1.4 to get VRB. Now let's get some things set up. We have 24 volts as our control voltage. We have 10,000 ohms as our collector outer resistor. And then we have 100,000 ohms at our base. So we're gonna go through the whole process here. So our first step here is going to be what is our base voltage? Now what we're gonna do, as I mentioned, is we're gonna take 24 minus the 1.4 and that's gonna get us 22.6 volts, right? Not the minus 0.7, it's not going to be 23.3 like you might think it's gonna be. Next up, what we're gonna do is we're gonna take this 22.6 and we're gonna divide it by the 100,000. That's gonna give us our base current. Now the reason why we like to use Darlington pair of transistors is that typically a transistor will have a gain of anywhere between 10 to 500. If you need to go beyond 500, that's when we start using these because we're taking the gain of Q1 and we're gonna multiply it by the gain of Q2 to get an overall gain. So if I had a 10 and 10, I'm gonna have 100 as my total gain in this situation. So again, I digressed a bit, I just wanted to make mention of that. Let's go back to this, using Ohm's Law and that's the craziest math we're gonna do in this whole circuit, that in subtraction. We're gonna go 22.6 divided by 100,000 ohms. That's gonna give us 226 microamps. Okay, now we have our base current. Everything's basically unlocked for us at this point because we now know that our base current times the beta of our transistor, which is our amplification factor or our gain, is gonna give us our collector current. So 226 microamps and in this case, we're gonna assume that the beta is 100. If it's not mentioned, you can make the assumption that the beta of a transistor is 100. So 226 microamps times 100, which is the beta, is gonna give us our collector current. In this case, that works out to be 22.6 milliamps. So we've got everything. We're off and we're running now. The hard part is done. Now, one thing you will learn if you go back to the other transistor videos is our emitter current is actually going to be our base current plus our collector current. And there's a way more better description of it in those other videos. I don't wanna go too far into it this time. Just take my word for it that my emitter current is my collector plus my base. So in this case, I'm taking my base current here, the 226 microamps, and I'm gonna add it to the 22.6 milliamps to get this emitter current down here. In that case, it works out to be 22.826 milliamps. Now, here's the magic of how this transistor works. And I don't know why I just love this part, but I think it's just brilliant. And whoever came up with this stuff, just, but let's take a look here again. This emitter current, if you notice the emitter here, it is connected to the base of Q2. So the emitter of Q1 is actually the base of Q2, right? So there you go. We're off and away again, because now we have the base. And again, I have no beta. So 22.826, we can assume that the beta is 100 is gonna give me my collector current. In this case, 2.2826 because I'm taking 22.826 milliamps times that by 100 gets me 2.2826 amps. Okay, now before you go too crazy on this and think that we're off and running, we can work out what our RC is, there's one thing that you need to really watch for. Let's take a look back down here at the whiteboard. This 226 or 2.2826 amps here is on this collector. You notice it comes up to this little nodey point here. That point also has 22.6 milliamps coming to it as well. They're going to come to this point and to this point and they're going to add, which means that my current going through my collector resistor is not going to be this. That's the one common mistake I see all my students make on this when they first start doing them is they think that the collector current down here is this collector current up here. It's not. IRC is something different. IRC is this C1 plus C2. In this case, that works out to be 2.3 amps. You have to add those two collector currents together because they meet at that node. Then we can laugh because we're done basically using Ohm's Law again. 2.3 times 10,000 will give us our RC. In this case, that's 23 volts. Then just the same as we've done with every other type of transistor, our VCC minus our VRC will give us our VCE. So we have 23 volts here. We have 24 volts here. That means that there must be a volt across this VCE. And that's the whole basis that we've just done it. We've gone through a whole Darlington pair transistor and there's nothing too crazy about it. Just to recap, let's just take a quick one last look here. VCC minus 1.4 gets me VRB. VRB divided by RB gets me IB. IB times beta gets me IC. IC plus IB gets me IE. IE becomes IB. IB times beta gets me IC. IC1 plus IC2 gets us IRC. IRC times RC gets us VRC. VCC minus VRC gets us VCE. And if I could right now, I would bow. There's a complete rhythm to this. It's almost like there's a dance to it. Every student that I've had that's worked these things through, find that once they get that little rhythm and how it all works out, find them absolutely easy and almost fun. I'm not gonna say they all find them fun, but some do. And then when they go back to the other transistor circuits, they are completely easy. That's a Darlington pair transistor. Again, we use them when we need to get a bigger gain than what a typical transistor can give us that 10 to 500 that a typical transistor will get us. Now, one question I have for you, my question of the day is, those of you who are into electronics and this is a legit question, oftentimes we see that the beta or the gain is sometimes called HFE. If you know why it's called HFE, can you do me a favor and I would love to know myself personally, can you leave a comment down below and let us know, all of us know, what HFE stands for and why they call it that? That's all I got for this week. Next week we'll go into how a transistor is used to switch. If you're getting any value out of these things, please hit subscribe, ring that notification bell, leave comments down below, share this with your friends. If you're in school, share them with your buddies, share them with your mom, your pop, your grandpa, your grandma, anybody who's into electricity, I'd love to keep getting the word out. And as the word starts to grow, I can start making more and more of these things and I absolutely love making these. So we'll see you next week. Have a fantastic week, stay safe and stay classy.