EST 130 BASICS OF ELECTRONICS ENGINEERING || Transistor - Working - Configurations -Current gain

Welcome to the 11th lecture of Basic Electronics Today we are going to discuss Working of an NPN transistor, different configurations of a transistor, current gain of a transistor We are going to discuss these things First, we are going to look at the working of an NPN transistor The working of an NPN transistor is explained by making the active region of the NPN transistor to operate You have learnt how to operate an active region in the last lecture Emitter based junction is forward biased Collector based junction is reverse biased This is an NPN transistor N region, P region and N region This is an emitter based collector This emitter based region is forward biased This N region is the negative of the battery This P region is the positive of the battery Collector based junction is reverse biased This N region is the positive of the battery This P region is the negative of the battery This is a PN junction There are two PN junctions in a PNP transistor this is a p-n junction, and this is another p-n junction this is forward bias, and this is reverse bias when this is forward bias, where do the electrons from the emitter inject? they inject here where do the electrons from the emitter inject? to the base, and then to the collector when this is forward bias, what is the negative potential of the battery? it attracts the electrons here always the direction of electrons is opposite to that of current so in this case the direction of electrons is towards here that's why the direction of current is towards here so the direction of current from the collector is initiated here then the direction of collector current is also to the back The direction of the current in the base region is in the opposite direction to the base region. Now let us see the working of the transistor. The working is done by connecting the transistor in an active mode. This is called an emitter-based junction. Forward bias is called a collector-based junction and reverse bias is called a collector-based junction. Forward bias on an emitter-based junction causes current flow across the junction. This current is called an emitter current. Emitter current is denoted by IE. Current flow occurs mainly through two components. One is the current due to electrons injected from emitter to base. The other is the holes injected from base to emitter. Emitter current is due to electrons injected from base to emitter and holes injected from base to emitter. Emitter current is the sum of the current due to electrons injected from base to emitter and holes injected from base to emitter. Total current is called IEN plus IEP. IEN is the current due to electrons injected from base to emitter. IEP is the current due to holes injected from base to emitter. The base region of this transistor is called thin. The base region of this transistor is called lightly doped. Since the base region is thin and lightly doped, only a few electrons are injected from here to the base. The rest of the electrons go to the collector. The electrons coming from here should reach the collector through the base. Since the base region is thin and lightly doped, only a few electrons are injected from here to the base. The base region of this transistor is called thin. The rest of the electrons go to the collector. The emitter current is the sum of the base current and the collector current. So, IE is equal to IC plus IEP. is equal to IC plus IB. There are two types of collector current. One is the emitter current that reaches collector. The current that is passed through the base and reaches the collector. The other is reverse leakage current. Reverse leakage current is the current generated by the thermally generated minority carriers in the collector region. The sum of both these is the total collector current. The total collector current is the sum of the current generated by the minority carriers in the collector region. There are some performance parameters. First is the emitter injection efficiency. The ratio of emitter current due to electrons injected by emitter to total emitter current is called the emitter injection efficiency. The ratio of electrons injected by emitter to the total emitter current is called the emitter injection efficiency. The ratio of electrons injected by emitter to the total emitter current is called the emitter injection efficiency. The emitter injection efficiency is the ratio of electrons injected by emitter to the total emitter current. The total emitter current is called IEN plus IEP. The ratio of these two is called the emitter injection efficiency. The next factor is the base transport factor. The ratio of current due to electrons arriving at collector to the current due to electrons injected by the emitter. The base transport factor is the ratio of current due to electrons arriving at collector to the current due to electrons injected by the emitter. The current due to electrons arriving at the collector is divided by the current from the emitter. The ratio of these two is called the base transportation factor. If you look at it, you will understand that the base transportation factor is the ratio of the electrons coming from the emitter to the base transporter. If you look at it, you will understand that the base transportation factor is the ratio of the electrons coming from the emitter to the base transporter. If you look at it, you will understand that the base transportation factor is the ratio of the electrons coming from the emitter to the base transporter. If you look at it, you will understand that the base transportation factor is the ratio of the electrons coming from the emitter to the base transporter. If you look at it, you will understand that the base transportation factor is the ratio of the electrons coming from the emitter to the base transporter. There are two types of collector current. One is the collector current due to the electrons coming from the emitter to the collector. The other is the reverse leakage current due to the thermally generated minority current. IC is equal to alpha IE plus ICB. This is the equation for the collector current in the case of a common base configuration. Alpha is the current gain of the common base configuration. We will learn about the common base, common emitter and common collector. Just remember this equation. Collector current is the sum of the emitter current and the reverse leakage current. Fraction of emitter current. The current coming from the emitter does not reach the collector. Fraction of emitter current. Alpha is multiplied to get the fraction. Reverse leakage current due to thermally generated minority current. This is called ICB. In the case of a common emitter configuration, beta IB plus ICE is called. In the case of a common base configuration, alpha IE plus ICB is called. In the case of a common collector configuration, gamma IB plus ICE is called. We will learn about these three equations. Now let us look at the three configurations. What is a common emitter, common base and common collector? A transistor is a three terminal device. Terminals are called emitter, base and collector. We denote emitter with E, collector with C and base with B. When we connect a transistor in an application, we need four terminals. Two terminals for input and two terminals for output. But how many terminals are there in a transistor? There are only three terminals. That is, two terminals for input and two terminals for output. So we take one terminal as common. We call that terminal as common terminal. Thus, the terminal we take as common can be the base, collector or emitter. That is why we can use this concept to configure three types of transistors. Common Base Configuration, Common Emitter Configuration and Common Collector Configuration. This is a two port model. Two terminals are used for input and two terminals are used for output. In the case of a transistor, there is only an emitter, base and collector. We take base as common. Base is used to apply input. Input is given by these two ports. This is used to apply input. Also, collector and base are used to apply output. In common Emitter configuration, the emitter is common for input and output. Therefore, the input is multiple of base and emitter. Output is multiple of collector and emitter. Common Collector configuration nickname is collector. The collector terminal is common for both input and output, because the input is in the collector base region or base collector and the output is in the collector-emitter or emitter-collector region. What is the current gain of a transistor? The output gain is the output divided by the input. What is the current gain? The current gain is the output current divided by the input current. At that time, what is the output voltage? The output voltage is constant and the output current is divided by the input current. What is the current gain? It is the current gain in both the configurations. In the common base configuration we see alpha as the current gain, in common emitter we see beta, in common collector we see gamma. In the other equation we saw alpha, in common emitter we see gamma. What is the current gain in common base configuration? In common base configuration, base is common for both input and output. Input current is the current coming to this input. Input current is the emitter current here. Output current is the collector current here. Output by input, change in output current divided by change in input current at constant output voltage. This is what we call current gain. In common base configuration, change in output current is delta Ic. Change in input current is delta I. Delta Ic divided by delta I. Constant VcV. Output voltage. This is across collector and base. At constant output voltage. At constant VcV. This is what we call current gain in common base configuration. The value of current gain is 1 in ideal case. But we get value slightly less than 1. Practical value is 0.95 to 0.995. Next configuration is common emitter configuration. In common emitter configuration, emitter is common for both input and output. Input is applied in base emitter region. Output is applied across collector emitter region. Input current is base current. Output current is collector current. Change in output current is delta Ic divided by delta Ib. This is what we call current gain. At constant VcV. Output is applied across collector and emitter region. At constant VcV. This is what we call current gain. In common emitter configuration, current gain is denoted by beta. The value of current gain is 20 to 500. This is the value of current gain in common emitter configuration. Next configuration is common collector configuration. In common collector configuration, collector terminal is applied across input and output. Input current is base current. Output current is emitter current. Delta Ic divided by delta Ib at constant Vec. This is what we call current gain. In common collector configuration, current gain is denoted by gamma. Now let us compare common base, common emitter and common collector. Answer is basic circuit. Input terminal is emitter. In common emitter configuration, input terminal is base. In common collector configuration, input terminal is base. Input terminal is collector. Input terminal is emitter. Common terminal is base, emitter and collector. Look here, input Resistance is less in common base Output Resistance results most in Common Base Next, the common recipient is the one that receives most amount of input Resistance Less Output resistance in commons The current gain denotes the alpha, beta and gamma in common emitter and gamma in common collector. Alpha is less than unity. Beta and gamma are high value. Voltage gain is less than 1 in common collector and high in common base and common emitter. Gamma is equal to beta plus 1 in common emitter and gamma is equal to beta plus 1 in common collector. Gamma is equal to beta plus 1 in common collector and gamma is equal to beta plus 1 in common collector. Gamma is equal to beta plus 1 in common base and gamma is equal to beta plus 1 in common base. Gamma is equal to beta plus 1 in common collector and gamma is equal to beta plus 1 in common collector. Gamma is equal to beta plus 1 in common collector and gamma is equal to beta plus 1 in common collector.