 Good morning, dear student friends. I am Dr. Sachin R. Gengze, Professor and Head, Department of Electronics Engineering at Vulture Institute of Technology, Sholapur. In today's session, we are going to have a look at some of the applications of open loop operational amplifier. The learning outcomes of this session include, after completing the session, the student will able to give an input signal for open loop non-inverting op-amp, sketch the output waveform for the same circuit. Similarly, given an input signal for open inverting operational amplifier, they can sketch the output waveform for that circuit. The content of this session include, we are going to have a look at open loop non-inverting configuration of op-amp. Similarly, open loop inverting configuration of an op-amp and then we will just have an introduction to open loop differential operational amplifier. As we already know, operational amplifier, which is also popularly called as an op-amp, is directly coupled high gain amplifier. It is available as a single chip or integrated circuit. It is a very versatile device and it can be used for amplifying DC as well as AC signal. It can also be used for numerous application to perform mathematical operation like addition, subtraction, multiplication, integration on analog signals. It can also be used for applications like designing oscillators, active filter, comparator, regulators and many more. This is a symbolic representation for op-amp. This is particularly for op-amp 741. As we know, there are two input terminals, inverting input and non-inverting input and there is one output terminal which is pin number 6 and op-amp require dual power supply of plus VCC and minus VEE. Let us compare the ideal and a practical op-amp based on different parameters. For example, voltage gain. For ideal op-amp, the voltage gain is infinite, but for practical op-amp it is not infinite, but a very large usually between 10 raise to 5 to 10 raise to 8. We say that the input resistance of an ideal op-amp is infinite, but for practical op-amp again it cannot be infinite, but it is between 10 raise to 6 to 10 raise to 12 ohm. The output resistance of an ideal op-amp is supposed to be 0, but in practical case a typical value of an output resistance of an op-amp like 741 is of 75 ohm which is very less. We say that the bandwidth of an ideal op-amp is infinite, but practically we know that that is not possible and a practical op-amp has again bandwidth product which is finite. Output offset voltage of an ideal op-amp is supposed to be 0, but in case of practical op-amp it is not 0, but it is of few milliholt. So, that is a comparison between an ideal op-amp and a practical op-amp. After that let us have a look at how a typical open loop op-amp works. If we say that V1 is a voltage applied to non-inverting terminal of an op-amp with respect to ground, V2 is the voltage applied to inverting terminal of the op-amp with respect to ground and if we are measuring V0 as an output voltage of an op-amp with respect to ground and A is an open loop gain of an op-amp, the working of an open loop op-amp can be very easily described by an equation of V0 is equal to A into V1 minus V2. In other words, the output voltage is equal to the differential voltage between the inverting and non-inverting terminal multiplied by the voltage gain. So, what happened because of this? As we know V1 is an non-inverting input, V2 is an inverting input, V0 is an output voltage and A is the gain. Now is this A is an open loop gain of an op-amp and it is very, very high. For example, in case of 741 it is equal to 200,000 and it as it is very much high what we can say that even a small differential when we apply a very small differential voltage that is difference between non-inverting and inverting input, even a small differential voltage will make the output of the op-amp very high. For example, if the difference between the V1 V2 is 1 volt and A is equal to 200,000, one can say that the output voltage is equal to 200,000 but we know that practically it is not possible to get 200,000 voltage. So, we say that whenever we say that the output of the op-amp is very high it is equal to or rather it is limited by plus or minus saturation voltage. For an open loop op-amp let us remember golden rules and what are the golden rules? See if you look at the equation V0 is equal to A into V1 minus V2 then from this we can derive two golden rule if V1 is greater than V2 that means the non-inverting input voltage even if it is slightly greater than inverting voltage then the output of the op-amp V0 is plus saturation voltage or plus Vsat. Similarly, if inverting input voltage is even slightly greater than non-inverting input voltage then the output of the op-amp is equal to minus Vsat and what is plus Vsat and minus Vsat plus Vsat is usually equal to or lesser than plus Vcc and minus Vsat is usually greater than or equal to minus Vee. So, we know we know that plus Vcc and minus Vee are the supply respectively positive and negative supply voltages of the op-amp. Let us have a look at the first circuit open loop non-inverting op-amp. So, if you why this is called as a non-inverting op-amp is simply because the inverting input is connected to the ground we are applying a voltage a sinusoidal voltage or a triangular voltage or a square wave voltage to the non-inverting input of the op-amp. So, what can be the output of this circuit? Let us have a look. So, as you can see over here the same circuit is again represented over here what I am applying at the non-inverting input is a square wave. Now how to find out the output of this circuit? Now output of this circuit finding out the output of this circuit is very easy. See the non-inverting input is connected to the ground and the golden rule say that whenever the non-inverting input is greater than inverting input the output is plus Vsat and when the non-inverting input is less than inverting input then the output is minus Vsat. So, for this for this half cycle the inverting non-inverting input is greater than the inverting input because the inverting input is always connected to 0. So, for the first half cycle the non-inverting input is greater. So, you can see that I am applying a triangular wave at the V in and that is why the output of the op-amp remains to be plus Vsat. Similarly, during this half cycle what happened? During this half cycle the inverting input is still 0 whole, but the non-inverting input now becomes negative and as it is a negative the inverting input which is 0 volt is greater than non-inverting input and that is why the output of the op-amp is minus Vsat. So, as you can see that if I apply a triangular wave at the input the output of the op-amp is going to be a square wave which is limited between plus Vsat and minus Vsat. This circuit is called as a zero crossing detector because you can see that I can locate the point where the input is crossing the zero level. Now, you can pause the video for some time and answer one question. In an open loop non-inverting op-amp circuit that which we have seen what happened if we apply plus one whole to the inverting input. So, in the previous circuit we have seen that the inverting input is connected to 0 whole, but instead of that what happened if I connect it to plus one whole or minus one whole. So, I think that you are you will be now able to draw the output waveform when I am applying when I for this particular circuit you have to simply apply the two golden rules which I have discussed. So, as you can see if I apply instead of applying instead of connecting the inverting terminal to zero if I connect a plus one volt over here I can see that the reference line will shift over here and then I will get a waveform like this. Now, this circuit is called as a level detector instead of zero crossing detector is called as a level detector because it is detecting a particular level of plus one whole. Let us go to the next circuit which is called as an open loop inverting op-amp. Now, this circuit differs from the previous circuit as now I am applying the input signal to the inverting input and the non-inverting input is now connected to the ground and then I need to find out the output voltage. Now, again for analyzing this circuit or for drawing the output of this circuit again I have to apply the same golden rule we say that if non-inverting input is greater than the inverting input then the output is plus V sat and if inverting input is greater than non-inverting input then the output is minus V sat. So, you can see that for this particular half cycle where the inverting input is greater because non-inverting is connected to zero the output is minus V sat and for this the inverting input is less than non-inverting because non-inverting is zero but inverting is negative the output is plus V sat. So, again I get a square wave. The last circuit which we will try to discuss is called as a differential amplifier. Now, you can look it over here in previous circuit one of the terminal inverting or non-inverting terminal was connected to ground and the signal was applied to the other terminal but in this case now we can see that the input is applied to inverting as well as non-inverting terminal both the terminals the input is applying this particular configuration of open loop of amp is called as a differential amplifier. Now, again in order to calculate or in order to draw the output of this circuit we need to apply two golden rule it depend upon what kind of signal you are applying over here what is a voltage level but output is going to be a square wave and I have to apply again the same golden rule of if non-inverting input is greater output is plus V sat if inverting input is greater output is negative V sat. So, with that we come to the end of this session and I am I am leaving you with two points to be discussed can you think of some more applications of op amp in open loop you have seen three application inverting amplifier non-inverting amplifier and differential amplifier. So, can you think of some more applications of open loop op amp and why is such applications are limited when you try to explore the answer of first question will come you may think that there are not many applications of the op amp than the zero crossing detector or a level level detector and why it is so that these kind of applications of op amp in open loop configuration are limited. The reference for today's session you can have with op amp and linear integrated circuit by Ramakan Gaiakwar and LIC linear integrated circuit by Roy Chaudhary and Shail B. Chai. Thank you dear student for patient listening.