In this tutorial, we are going to learn about Best Tutorial on Transistor.
Types of Transistor:
So we start firstly that how many types of transistors, basically these are of two types first is known as bipolar junction transistor and second is known as field effect transistor so today video is revolve around bipolar junction transistor so i should tell that we will discuss on bipolar junction transistor and this field effect transistor we will discuss in coming videos. The bipolar junction transistor is basically of two types one is NPN junction and second one is PNP junction what is this when we discussed on PN junction diode there by join one P type semiconductor and one N type semiconductor forms PN junction diode. Here is three SI units available as if we place P type material between two N types than it makes NPN junction and if we place N type material between two P type materials than it makes PNP junction. If you observes/see the basic structure P of than this is transistor bipolar junction transistor which is NPN transistor so it is N side, in between P side so this is N type semiconductor, this is N type semiconductor and this is P type semiconductor. So now we already know that what N type semiconductor is, what P type semiconductor. So if you see the PNP bipolar junction transistor it’s also forms exactly as NPN junction, this is P type semiconductor this in between this n type semiconductor its thin type of layer. The mechanism of working of transistor is same in this and this but the difference is where you assume the holes. there free electrons available and there is holes so you can understand this interchangers also but understanding is more easy when we discuss on NPN type junction so that’s why in every place when you study transistors bipolar junction transistors so by form NPN is base we can understands this and so the same mechanism for PNP also.
Structure of Transistor:
The basic structure of NPN junction we already observe. In this structure three sides are presents. We can see the properties of three sides. How is three sides see there one side, second side and there third side. One is emitter, second is collector and in between this is base. E stands for emitter, C stands for collector and B stands for base. Now we understand the basic property of these. That this is emitter, base and collector so where is the difference is. So the difference is in the thickness and in doping level of these. So the first point is thickness and second is doping level. The thickness and doping level is different of all,
Firstly the thickness of emitter is medium thickness and the properties of base we can write there it’s very thin it’s of some micrometer size. So this full VBAT is very small unit therefore by combining billions of transistors we form one integrated circuit. Integrated circuit is also very small so you can understand that this VBAT is own how much small. it’s of some 100 microns and this base is of only some microns only so relatively its very thin and this emitter is little wide and this collector is in respect of emitter is more wide. so now if you see the doping level its very less doped base, base is lightly doped if see the emitter its highly doped so the doping level is very high and this collector is moderately doped so moderately doped by see the figure you can think that we can make the collector as emitter and we can make the emitter as collector by interchangeability we can use this but this is not so the transistor is transistor. So we cannot interchange this you can see there is difference in thickness and doping level.
Symbol of Transistor:
The PN junction diode symbol is as this so one is p side and other is n side if current flows in this direction than this is in forward bias it allows the current to flow and electric field in this direction so if current want to flow in this direction so it stops the flow of current than we called this situation is reverse bias. so this is the symbol of this PN junction diode but there the symbol of transistor is not as this its somewhat different normally a circle draws and by straight line one base indicates so this is base and by two slant lines one is emitter and other is collector so you can understands that which one is emitter and which one is collector so see in emitter one arrow is available arrow is in this direction or available in this direction also. This direction tells that this is PNP transistor or it is NPN transistor so if i place arrow there or in opposite direction as this so this tells that this side is emitter and this side is collector. because emitter is this so we have to place arrow in this line than in this case if this is NPN transistor so the arrows direction is as this. The logic behind this we will discuss after sometime. From there we get three points. One is this, second there and third is there. So from there the connecting wires releases and if tell there about the PNP so PNP is like this that this is base this is collector this is emitter and this arrow is in some this direction so this is base this is collector and this is emitter. There three connecting wires are attaching in three points so one connecting wire we removes from base second from emitter.
Working of Transistor:
Now we understand the logic that where in which direction arrow should be place, Now how understands in this type of cases keep this in mind that junction of base emitter is always available must in forward bias. So you understand that in NPN and PNP in which direction you have to place arrow and this arrow indicates the direction of current. Now if you see there than you find that there this collector is n this is also N side and base is P side and because it’s PNP so collector P, base is N and emitter is also P side. We know that forward bias is when the direction of current flow from P to N direction and in reverse bias when the tendency of current is in the direction so in this case we called it as reverse bias so it’s in reverse bias. For forward bias the current can flow from P to N side there this is P side this is N side so the direction of current flow from P to N means in forward bias. So the current flow in between base and emitter is as so the P and N is in forward bias. there this is p side this is N side so the current flow between base and emitter is as this P and N junction diode must in forward bias means current can flow from P side to N side so the direction of arrow is this so you understands that how we can draw the arrow and how we can represent the PNP and NPN transistor by symbol.