# Beginner Electronics - Beginner Electronics – 22 – NPN Transistors

## Beginner Electronics

29 Lessons

### Beginner Electronics – 22 – NPN Transistors

what is going on everyone my name is could more and welcome back to electronics episode number 22 and today we will be learning all about

transistors the very building blocks of computers and integrated circuits which we will be learning about in the near future now understanding how a transistor works and functions will help

us understand how more complex decision-making circuits work at their lowest level and also we will quickly see the power of the transistor as well as many other components as the series

continues on and we begin to work with all these components together now this episode is going to be only a brief description of how a transistor functions and how we can use the

transistor I will not be going full on in depth with how it transistor works at the lowest level with all the calculations that you may need and that is mainly because one for this series

and building an 8-bit computer like we will be doing we don't need to know that complex information about our transistor and second of all when we actually begin to use transistors in circuits which we

will in just a couple of episodes you'll quickly see how we can use them in an actual circuit and it'll become fairly understandable without even knowing all the math behind it but of course if

you're really interested in messed up definitely look up a few articles and videos on the subject because you will learn a lot about transistors if you do look up some more information and I do

have links down below in the description to help you out with that but I will be explaining – all we need to know to follow along with the rest of this series here about a transistor now a

transistor can be used sort of like an electronically operated switch just kind of like a relay in a sense but they can also be used to amplify signals and do much much more and as always there are

different types of transistors some are rated for lower currents and voltages and others are built for much higher voltages and currents and some even have slightly different functions and work a

little bit differently but today we will be looking at a fairly common transistor type the bipolar Junction transistor and bipolar Junction transistors BJ T's come in two different types they come in the

NPN type which is what I have right here the schematic symbol for an NPN transistor but they also come in something called a PNP type transistor which I will not be getting into in this

tutorial here but the links down below in the description which provide you much more in-depth information about transistors do cover PNP transistors and contain more complex information about

transistors in general but let's just take a look and learn about the NP and transistor here now this type of transistor has three connections the one on the left is called the base

connection the top one is called the collector and the bottom connection is going to be called the emitter here now think back to what we did with relays a relay if we applied power to the

electromagnet would allow a switch to turn on and off well a transistor can act very similarly basically if we do not apply a voltage or a current to the base if we don't do anything to the base

then the collector and emitter are prevented from having electricity travel it acts like an open switch and electricity won't travel there just like a relay however if we apply a small

amount of voltage and current to the base then we will allow electricity to flow from the collector to the emitter kind of like a closed switch now that is only an extremely basic version of how a

transistor works in reality basically if a small amount of current travels from the base to the emitter if we have a very small amount of current traveling here and we also have approximately 0.6

volts traveling to the base then we allow a much much larger current to flow from the collector to the emitter it actually amplifies sort of the current going from the collector to the emitter

in reality that is kind of more what's happening and of course there's much more to it than that but I won't be explaining that in this tutorial series so let's go build a circuit with this

transistor to see how it differs from a relay so let's begin by drawing our transistor here our NPN transistor which looks something similar like this and it has an arrow on the emitter that's how

we know it is an NPN transistor and what I'm going to do is on the collector here I'm going to attach a resistor and I'm going to attach a resistor because I want an LED to be right here and

whenever we have an LED we probably want a resistor in our circuit and this LED is going to be hooked up to the positive terminal of course to our battery and I'll go ahead and connect the negative

terminal of our battery ground to the emitter pin of the transistor here now if we just tried to run this circuit or we made the circuit as it is right now then it would not work because we aren't

applying any voltage or current to the base connection here so it acts like an open switch and electricity won't be able to flow through the circuit and light up

the LED it won't work just like our relay circuit now you may at first think that to make this work we have to hook up the base of the transistor to the positive terminal of the battery but

this in fact will not work and it doesn't work simply because that's not how it transistor works now if you knew a bit more information about the lower level workings of a transistor you would

probably understand why this circuit doesn't work all we need to know is that we need a smaller amount of current and a smaller amount of voltage to go to the base to make this circuit work so we can

either have another smaller power source hooked up to this base connection right here or we can just take the positive terminal of our battery and we could hook up a high valued resistor to the

base so if we made this high valued resistor right here then our circuit would work so in the case of what I'm going to build in just a few moments here I use a hundred K ohm

resistor a hundred thousand ohm resistor here that way our circuit works and to be able to control it a bit better just kind of like we had in our relay tutorial series in our relay circuit I

am just going to go ahead and draw in a push-button schematic symbol here this way when we push this button we will allow electricity to go to the base the LED should light up if the button isn't

being pushed then electricity is not going to the base so everything should not work it should act like an open switch and the LEDs should not light up so let's go ahead and build this circuit

now what I have here is a 2 n 2 2 2 2 NPN transistor this is one of the most popular types of NPN transistors that has been made and as you can see it had a little rounded edge and then on the

left side there is a little flat edge and I know by looking at the data sheet for this transistor if I look straight on to the flat edge from left to right the pins are emitter base and then

collector now of course your transistor may be different so take a look at your datasheet to figure out what pins go to wear on the transistor so we are just going to follow essentially the

schematic that we had made just a few seconds ago we are going to hook up our emitter directly to the negative terminal of our battery so I have a wire going to the

negative power rail of my breadboard that's being connected to the emitter pin of my transistor next I have my LED here I have the longer leg or the anode going to the positive power rail of my

breadboard and the shorter leg of the LED we are just going to connect a resistor to that and going to the collector of the transistor now in my case I'm using a three volt power source

or two double-a batteries and for this resistor right here it's a 200 ohm resistor for my LED so we have our LED and 200 ohm resistor hooked up to the collector of our transistor and now we

need a way to control the base of the transistor so that we can turn the transistor on and off kind of like our realated and for that I just have a simple push button here I'm going to

hook one of the legs of the push button up to the positive rail of my battery or rather my breadboard so we'll get that terminal hooked up to the positive rail of the breadboard and then from there

I'm going to have a 100,000 ohm a 100k ohm resistor going from the other terminal of this push-button to the base of my transistor here and remember we need this high-valued resistor just

because of the way that the transistor works which is a bit too advanced for this tutorial series but anyways we want to have a high value resistor right here so if we press the button we will allow

a small amount of current to flow to the base of the transistor which should hopefully allow electricity to flow from the collector to the emitter allowing this led to turn on which it does so

very similar to the relay circuit we had when we press the button we activate the transistor allowing the LED to light up now what we can do instead to make this project a little bit more fun is I took

out that 100,000 ohm resistor there and we aren't even going to be using this button anymore what I'm going to do is I'm going to hook up a regular wire to the base of my transistor here so just a

regular wire and I'm going to hook up another wire to the positive terminal of my battery the positive power rail of the breadboard and what we can do is we can actually use our finger to be

a resistor in this circuit so what I'm going to do is I'm going to take the tip of my thumb here and I'm going to place this wire on the tip of my thumb then I'm going to place the other wire here

to the tip of my thumb as well not quite touching and as you can tell I can actually light up the LED by just putting the wires on the tip of my thumb because my thumb is actually acting like

that 100,000 ohm resistor of course it's not a hundred thousand ohms but it is acting like a resistor which allows us to power this led just by the tip of our finger and that actually has a couple of

uses in the real world you can even hook up a photo resistor which is essentially a resistor that changes based on the amount of light that gets to it so you can actually have a day or night

detector which is pretty cool there are a lot of uses that we can make just using one single transistor I know that this is a strange tutorial I didn't go full-on in depth into transistors that's

a bit out of the scope on this tutorial series but down below in the description I do have a few links where you can learn more about transistors that would be a great thing to do but it's not

necessary that you do that for this tutorial series thanks for watching everyone and I'll see you guys in the next video

In this episode we discuss the basics of NPN transistors!

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