 Hello, welcome to the session on Transformer Coupled Amplifier. At the end of session, students will be able to explain the operation of Transformer Coupled Amplifier as well as they can analyze the parameters of Transformer Coupled Amplifier. Contents are like this. So, why there is need of Transformer Coupled Amplifier? In this previous sessions, we have seen why there is need of coupling that we need to improve the gain of the amplifier. But here, while doing so, we are employing the various coupling schemes. For first one, we have seen RC coupled amplifier. In that, there is loss of signal and to over that, we have gone through this Transformer Coupled Amplifier which allows you the coupling with impedance matching. So, that is the advantage of this Transformer Coupled Amplifier. So, here output of the first stage is coupled to the input of next stage where coupling device used is Transformer. So, we are using the Transformer at the collector of the first stage as well as in the further stages. So, you are providing the output of Transformer that is Transformer secondary to the input of base of the next stage. So, effectively load is reduced in the RC coupling and because we have the parallel combination of the load with the input impedance of the previous stage. So, while doing so, there is a reduction in the load and therefore, we are not able to obtain the proper impedance matching. So, by proper selection of the turns ratio of the primary and secondary windings, we will achieve the advantage of impedance matching. As RC is replaced by the Transformer and load value that is value of the resistance at the collector is varying that is reflected load over there, shift the DC voltage supplied by the VCC at the collector. So, it is useful when the load value is small. Figure 1 shows the two stage Transformer coupled amplifier where we have input Transformer which is a step up Transformer always to improve the strength of the input signal and the further all the Transformers are step down Transformers. So, these are the coupling Transformer which are step down Transformers. Here we are employing the bypass capacitor as well as you can also have the parallel capacitor with this register RB to obtain the good signal strength or to avoid the interference of the unwanted signal. So, Transformers must be shielded to avoid the unwanted pickups. If you convert the figure 1 into the equivalent form or the simplest form, we can represent it with this kind of figure that is approximate model or the equivalent circuit. So, for example, here input Transformer has the turns ratio of 1 is to 4 and the collector circuit of first stage having the primary of the Transformer which is a step down Transformer or the coupling Transformer. So, here ratio is 5 is to 1. So, this secondary of the primary secondary of the Transformer will provide the input to the next stage. So, here we must know how much should be the impedance of this all Transformers and that is very important while selection of the turns ratio. Therefore, we must calculate the reflected load. So, if you find this Z 4 is the load impedance and Z 2 is the impedance at the input stage or impedance of the first stage at the collector. So, you need to find the relationship between them for calculation of turns ratio. So, there is a condition of the maximum power transfer that is Z 2 and Z 4 should be equal to 1 upon H O E. So, what is 1 upon H O E? 1 upon H O E is the output impedance of the transistor and when you do so, you will get the proper impedance matching. So, while selecting the Z 2 or Z 4 nothing but the resistance of the primary windings of the coupling Transformers, you need to find that value should be nearly equal to 1 upon H O E. Z 4 gives you the equation for the reflected load. So, what is Z 4? Z 4 is the load at the collector of the coupling Transformer and you know the equation for the reflected load that is n 1 upon n 2 square into R L. R L is the load connected at the output of the coupling Transformer or output of the your total Transformer coupled amplifier. So, with this you will get the equation for or value for Z 4 and that Z 4 you are again matching with the 1 upon H O E. So, V 1 can be calculated equal to n 2 upon n 1 into V in. This is with the help of voltage transformation ratio and as you know this input voltage and the V 1 that is the ratio of this turns ratio will give you the output of the secondary of the Transformer. Therefore, V 1 is equal to 4 times V in due to the voltage transformer ratio, transformation ratio of the step up Transformer at the input of amplifier. Next, with this I can calculate A V 1 equal to V 2 upon V 1. So, V 2 is the voltage at the output of this 4 stage and V 1 is the input at the 4 stage. So, this ratio will give you the equation of A V 1 same way I will get the equation for A V 2. Therefore, I can multiply these two values. So, calculate the total gain provided by the Transformer coupled amplifier and here rather than the value of gain we are interested in the impedance matching. So, how do you calculate the turns ratio? If the load value is 16 ohm and effective load resistance is of 10 k low ohm then what should be the turns ratio? So, this is the 16 ohm connected at the output of the amplifier and the 10 k low resistance is connected or we can say that is the reflected value of the load that is 10 k. So, to calculate that we have the equation that is Z S equal to n 1 by n 2 square into Z L and this is the heat to calculate the value of turns ratio. So, Z S is what? Z S is your 10 k nothing but effective load resistance and Z L is 16 ohm. So, we can find this value by putting the equation. So, n 1 by n 2 is equal to under root Z L square upon Z L where Z L dash is 10 kilo ohm and Z L is 16 ohm. So, it comes 25 ohm sorry it is 25. So, we can say n 1 should be equal to 25 times n 2. So, this is the equation to calculate the turns ratio and this is what for the coupling transformer and that is why we can say here in the coupling transformer we have n 1 greater here see the frequency response of the transformer coupled amplifier which is not proper or we can say it is not constant over the range of frequency. Therefore, it is not suitable for the high frequency values as well as for the low frequency values, but it provides the proper impedance matching. Therefore, we will list out this advantages that it has excellent impedance matching high gain due to the impedance matching, but it has poor frequency response and the noisy output and as we are using the coupling transformer at each stage and at the input stage circuit becomes complex and bulky as well as costly. Therefore, you will have this disadvantages. So, this type of amplifier is widely used in the impedance matching that is at the input stage or at the output stage these are the references. Thank you.