So, the topic we are going to discuss today is also about the last stage of an amplifier, all are last. Now, today's topic is on power amplifiers and as we all know, power amplifiers always would be the final stage in an amplifier. Now, if you take the example of the public system, which we have been talking about, starting from the microphone all the way to the loudspeaker, you would see that power amplifiers come just before the loudspeaker. It is the power amplifiers which actually drive the signal through the loudspeaker, which makes us to hear the audio well. Now, power amplifiers are very, very different from all that we discussed so far. We talked about common ampere amplifiers, we talked about common base amplifiers, we talked about common collector amplifiers. In those amplifiers, our consideration was mostly gain input resistance, output resistance and so on. And when we talked about feedback amplifiers, we saw how we could improve these parameters, especially input impedance and output impedance, depending on the type of the amplifier. We saw how we could get almost, let us say close to ideal condition by applying negative feedback. So, our consideration in the case of feedback amplifier was to how to make our amplifier, an ordinary amplifier, how to make it say close to ideal. When we talked about multi stage amplifiers, we said multi stage is the way you go about when you actually implement an application such as a publicator system or even in an op amp, we saw that you have at least two to three stages and the final stage is the output stage or the power amplifier stage. So, here the considerations which we are going to talk today are very, very different from all that we talked about so far. Now, let us get into the topic, I would quickly go through the kind of topics I plan to cover depending on the time. Now, when we talk about power amplifiers, they are conventionally classified into what are called class A, class B, class AB and class C. What we will do is, we would see the classification initially and then we will talk about class A power amplifiers, we would see their transfer characteristics, we will also observe their signal waveforms, we will also see about their power dissipation and power conversion efficiency we will see. Then, we will talk about class B power amplifiers, once again we will see the transfer characteristics, the power conversion efficiency and we will also talk about power dissipation. Now, once we talk about class B amplifiers, we need to talk about what is called the cross over distortion and we also need to wonder or rather worry about how to reduce the distortion and therefore, we have this intermediary between class A and class B called the class AB power amplifiers. We will see how it operates and we will talk about a simple biasing scheme for a class AB circuit and finally, we will just quickly talk about power BJTs and some of their basic characteristics. Now, one very important thing to remember in this particular topic is, the transistors which we use here are very different from the ones which we were considering so far, hence the word power BJTs. Now, so far the BJTs we were using, they were what are called a small signal, they are even sometimes called small signal amplifiers such as BC 147 or 547 or BC 109 and so on. Whereas, when we talk about power BJTs, the consideration is very different, they are primarily meant for high power application therefore, in terms of the size also they would be very very different. So, we will see quickly, we will talk about power BJTs. Now, let us get some idea about this topic of power amplifiers or the output stage in an amplifier. Now, the power amplifier or the output stage as I said right in the beginning of my lecture is the final stage of any practical amplifier, why is it so? Because it is in the final stage, you have to connect the output of the amplifier to the load. So, power amplifier, its main function is to drive the load. Now, again another very major difference from all that we talked so far and this particular amplifier is, so far we were talking about large signal levels, we did not concern ourselves with small signal. Now, in this particular amplifier, we are actually concerned about not the small signal, but large signals, why is it so? Because after two stages of amplification or three stages of amplification, let us say in a power, let us say a publicator system, the signal levels we are talking about are very large, take the example of a publicator system. The signal levels we are talking about could be of the order of say 20 or 30 volt peak to peak, could be quite high as compared to small signal. When we talk about the BJT amplifier, when you did in the laboratory, the levels you are talking about are say typically at the most let us say peak to peak 1 volt. So, here we are talking about large signal and that makes a very big departure from all that we are talking about. So, therefore whatever models we use so far, which were the small signal models, we cannot use them anymore. So, this something which we need to keep in mind very much. So, therefore we will not use any small signal model. And if you remember from the example we took in the, when we talked about multi stage amplifiers, I took a numerical example to illustrate a multi stage amplifier. And there I said that the multi stage amplifier, the final stage of the multi stage amplifier in that particular example had a unity gain. So, almost always power amplifiers are designed for unity power gain rather sorry unity voltage gain. And they have large current gain therefore they have large power gain. So, even though they have unity voltage gain because of the large current gain, they have a large power gain. And we know that power gain is nothing but voltage gain times current gain. Now, because we are talking about large signal currents at the output side, power amplifiers must have very low output resistance. So, this is definitely easy to understand. Whenever we have to drive lot of current, we need to ensure that the source resistance is very small. So, here we have a controlled voltage source. So, we need to make sure that the resistance are small. When we say small here, we would be talking about most of the time resistances say less than an ohm, much less than an ohm. Again higher the power application, much much lower the output resistance. Now, when we talked about small signal amplifier so far, we took something from granted. Why did we talk about small signals? We talked about small signals because we said that if you could keep your input signals in a common emitter or a common base or a common collector amplifier to be say about 10 millivolt or so. We said then we could assume that the distortion, the non-linear distortion is almost not there. So, therefore, we could assume the amplifier to be linear and in almost all the cases, we would find that the small signal approximation is fairly accurate. Now, here unfortunately, since we are our signal levels are much higher than 10 millivolt and they could be at the order of 10s of volts or at least a few volts. Generally, it would be 10s of volts if we talk about a kind of a power application. Now, here therefore, one you will have non-linearity. So, one very important parameter in the design of a output stage or a power amplifier is the amount of total harmonic distortion or what is called the THD. So, power amplifiers will always have some amount of THD as compared to normal small signal amplifiers. So, we need to kind of specify this. So, when you buy say a publicator system, they would mention that the total harmonic distortion is so many dB's and so on. Now, the THD or the total harmonic distortion is the RMS value of the harmonic components of the output signal excluding the fundamental. Now, again another extremely important parameter when we talk about an output stage is the efficiency. Now, this is something which we did not worry at all so far. We did not even use this but efficiency so far because when we talk about a small signal amplifier, the signal levels we are talking about are very small say milli volts and the typical power we are talking about again would be at the most let us say 10 to 20 milli watts very small. Therefore, even though our amplifiers were highly inefficient that did not bother us because even if you are talking about let us say a 10 percent efficiency in an amplifier which is delivering let us say 10 milli watt of power.  But unfortunately, when you talk about a power amplifier since the power levels we are talking about are large. By the way, when we talk about power amplifiers we generally talk about applications which are which deliver power of say more than a watt let us say typically 10 watt or above. You would say 10 let us say 5 watt or so. So, we are talking about power power's order of say 10 watt or more. Therefore, efficiency is an extremely important parameter for an amplifier because now it is not just the amount of power we are wasting. But in some applications that may be an important consideration but in most of the applications it is the amount of power you need to dissipate that will be the main concern. So, therefore, if I have an efficiency of only 10 percent and I am if I talk about let us say a 10 watt then I need to somehow dissipate 90 watts of power. Now, that is definitely not an option. Therefore, we have to really be concerned about efficiency. Now, low efficiency would automatically mean much larger power dissipation and the reason why power dissipation is a problem for us is the following. Two reasons one is it is very difficult to dissipate the power and to keep the temperature and I am sure all of us are familiar with let us say if you visit a small let us say a mobile transmitting station or any electronic application where you have large amount of power. You will always see a huge amount of cooling being done through fans and so on. Sometimes even they would use coolants to do that. Now, so that is one concern to dissipate the power. Now, another very major concern is we are talking about semiconductor devices. Now, so far we never ever worried about the how much our device would get heated up or so because the powers we are talking about were a few milliwatts, but now we are talking about hyper high powers. Therefore, we need to be concerned whether our device would get heated up. Now, if our BJT gets let us say heated up beyond say 150 degrees, it will get damaged immediately. It is completely useless. In fact, it may not be a bad idea to may be just touch the body of one of this power transistors which you would find the bottom of or just the rear side of a publicator system or sometimes even in power supplies. It is a good idea to just touch it. You will always see it be warm and we are talking about 150 degrees which is very, very high. So, you need to ensure that the temperature of the BJT junction temperature does not increase and it is kept within as close as possible to the ambient temperature. Now, we are talking about say an application where you are using battery like especially a portable kind of application. Then the power efficiency is the concern there is the amount of reducing the drain in the power supply. Now, as we said the transistors used here are very special transistor and typical power dissipation capabilities of these transistors would be a few watts and sometimes may be hundreds of watts. For example, a very popular NPN transistor which you may be familiar is 2N3055 which has a dissipation power of 125 watts. So, we are talking about large power dissipation values. Now, we could design an output stage using both discrete and integrated circuits both are there in use. Now, these days you would find lot of power amplifier ICs available and which has much better features than the discrete ones, but what we are discussing here are basically concepts. So, it does not matter we are talking about discrete or integrated. Now, as I said right is the beginning, when we talk about power amplifiers we classify them into class A, class B, class C and so on. Now, this is done on the basis of the shape of the collector waveform in response to the input signal. Now, we would assume the input signal to be sinusoidal. Now, what we have here is a sketch of the typical collector current waveforms in 4 of these categories. Now, let us look at the first one. Now, the class A amplifier what we see here is that we have the signal here sinusoidal signal here and this is the collector current. Now, what you would see here is that even when the signal is negative even at the extreme negative excursion of the signal you see that there is still current, which means that this particular current IC which is the Q-SAN current or the operating current is greater than the peak value of the signal. So, this is a particular this is a very important feature of a class A amplifier. So, in a class A amplifier you would ensure that even for the largest swing of the signal your the amplifier would always have current this current the negative peak the current does not go below 0 you would ensure that. Now, that is class A when you come to class B what we see is that in a class B amplifier we would actually use two devices one device for one half cycle and the other device for the other half cycle. So, what we see here is the typical class B classification where the current would be in the previous case it was flowing throughout. So, if you talk about a conduction angle here it was 360 in this case the conduction angle is 180 degree. So, that is the classification of a class B and as I said because you are only taking care of one half cycle you need to have two devices working in tandem or in a complementary fashion. So, one device would take care of the positive half cycle the other device would take care of the negative half cycle. So, that is how a class B amplifier works. So, the conduction angle here is 180 degrees. Let us now talk about class C amplifiers. Now, class C amplifiers are amplifiers where the conduction angle is less than 180 degrees. Now, class C amplifiers are very special cases and we will not worry much about them. Now, class A amplifiers are used in very high power applications. So, generally these are very special kind of applications we will not worry much about them. What is important for us are class A, class B and class AB. Now, class AB is something which is in between class A and class B. We said class B the conduction angle is 180 degrees and in a class A it is essentially 360 degrees. Now, class AB is a case where the conduction angle is greater than 180 degrees, but less than 360 degrees. So, it is slightly more than 180 degrees and we will see why. So, let us look at these in some detail. So, what we saw in the signal which we just now saw was in a class A amplifier, the amplifier is biased in such a way that the DC operating current without the signal that was greater than the peak of the signal current I p, we saw that. Now, that is why we said in the case of a class A amplifier, the amplifier or the device in that amplifier conducts for the entire 360 degrees. Now, what are examples of class A amplifiers? Now, the amplifiers which we studied so far common emitter, common base and common collector, these amplifiers belong to the class A category. So, these are amplifiers where the device conducts for the entire 360 degrees, the entire the conduction angle is 360 degrees entire period. There is no interval during the signal, the device is not conducting. So, our common emitter, common base and common collector belong to the class A category. Now, what are class B? As we saw from the waveform there, the collector waveform of class B amplifiers, what we saw that these amplifiers were kind of biased at 0 DC current. So, therefore, they conducted only when the signal came and we said you would have two devices. So, normally there is no conduction and as soon as the signal comes one device conducts for the one half cycle. So, one device would take care of the positive half cycle, the other device would take care of the negative half cycle. Therefore, since they conduct only for half period of the sine wave, the conduction angle is 180 degrees. Now, as I said because they conduct only for 180 degrees, you need two such stages or let us say two such devices. Now, what is actually done is you would combine the currents from these two stages. So, that when it flows into the load you have a kind of continuous conduction. Now, class A B amplifiers as we saw in that the waveform there, these are biased at not 0. In class B, we would bias it at 0, which means there is no signal the amplifiers or the BJTs are off. But in this case, if we would bias the transistor at a very slight value of DC current, but this would be much smaller than the peak current of the sine wave. Now, if you compare this with class A, a class A amplifier we biased making sure that the biasing current is much greater than the peak of the sine wave. But here, we would bias it at a extremely small DC current, we will see why and how much. Therefore, the class A B category the transistor conducts for a period greater than 180 degrees, but much smaller than 360 degrees. Now, class A B also requires two class A B stages. Now, again just like the class B, you would kind of combine the currents from these two transistors and they are combined so that they would flow in a combined fashion into the load. Now, when we talk about class C amplifiers, now this was the waveform we saw in the last one, where we saw that the transistor conducts only for an interval which is less than half period. So, the conduction angle was less than 180 degree. Now, the output current waveform is actually a kind of a periodically pulsating waveform and so this kind of amplifiers are used for very high power application such as let us say a transmitting station, where the kind of powers you are talking about are in the orders of kilowatts or hundreds of watts. In those kind of situations, you would use a class C amplifiers and then what is done is the currents are passed through a parallel LC-LC circuit tuned to the frequency of the input sine wave and we will not this is a very special class and we will not study this because this is generally you would never ever come across a class A amplifier. Now, let us look at class A amplifiers in detail and then let us see why class A amplifiers are not preferred even though they conduct for the entire 360 degrees which is the ideal situation, we will see why they are not. So, we need to see in detail their operation. Now, you can think of a class A power amplifier as an emitter follower. In fact, that is the most popular choice because we know that emitter follower has low output resistance and we saw right in the beginning that one of the most important requirement of a power amplifier is that it should have low output resistance. Therefore, the obvious choice from the point of view of what we studied so far is to choose an emitter follower.  So, what we have here is basically a two transistor kind of combination. Now, what is done here is this stage here which we see in the bottom that is q 2 and this diode here and the resistor. Now, this are the q 2 is biased through this particular diode in such a way that there is a current I flowing all the time, a DC current I flowing all the time. Now, what we will do is the when we apply a signal here, we want to see how exactly the output looks like. Now, as we said in this particular case since we are talking about a power amplifier, we are actually interested not in this one signal operation but in the large signal operation. So, let us see how this particular circuit operates. So, to recap what we have here is a q 1 which is the one which gets the signal and it is biased through this two transistor combination and we have a emitter current flowing which is I e 1 and then what happens is a current I e 1 will be equal to I plus I L and I L is the current flowing through the load and we have the output voltage taken across the load. Now, what we need to see is for seeing the large signal operation, we need to find out the transfer function rather the transfer characteristics of this particular stage. Now, what we saw that it was biased with a constant current I supplied by the second transistor and we saw that the current flowing through the first device I e 1 is equal to I plus I L where I L was the current through the load. Now, we need to ensure that when we choose I e we need to ensure that the bias current I e must be greater than the negative peak of I L in order to ensure that q 1 is always in the active mode. So, this we saw when we saw the signal waveforms. So, when we design such a stage we need to ensure that the particular current is chosen such a way that the it exceeds the negative peak. So, that even when we have the negative peak still you have a certain value of DC current. Now, we can write a very simple equation for the transfer characteristics which as we saw the signal was supplied to the base of that transistor and we have a V B drop there. So, output was this was an emitter flow. So, output is taken from the emitter therefore, the output voltage is nothing but input voltage minus V B e 1 and this is an N P N transistor. So, this is the equation. Now, the important thing to remember here is this value of V B e 1 depends on I e 1 and it definitely also therefore, has bearing on the value of I L. Now, if we can neglect the small variation in V B e 1 due to I e 1 variation and we know that the being an exponential characteristics for a very small change in V B e 1 would get large current variation. So, if you assume that these variations in V B e 1 are small then from this equation we see that the V out versus V in characteristic is linear. Now, if you sketch it this is how we would get. Now, from that particular equation we wrote V out is equal to V i minus V B 1. So, we see that we see this particular characteristic. Now, what is important notice here is we assumed this to be linear which is not a bad assumption. Now, we need to be concerned about the upper limit and the lower limit and on the x axis we have V i and the y axis we have V out or V naught. Now, the upper transistor being in a common collector kind of a stage we are taking output from the emitter therefore, the maximum value the emitter voltage the maximum value of the emitter voltage is nothing but the V c the V cc the positive V cc minus V c sat that is the maximum voltage you can have. So, till that point you can operate. Now, coming to the absolute you can when you talk about the negative half you can think about 2 limits. Now, in case 1 the the absolute limit is the limit when that particular transistor would go into saturation. So, the bottom transistor let us see the circuit again. Now, so this is the first transistor Q 1 here now Q 1 the output voltage here can rise as high as V cc minus V c sat. So, that is the upper limit here. Now, coming to the lower limit the extreme is minus V cc plus V c sat. So, that is the extreme limit, but again depending on the current which you have chosen here you can have another limit. So, in case you are constrained by the current you have chosen there then the negative limit will be minus of I R L we must remember that we have chosen I such a way that the peak of the it is greater than the negative peak. So, if that is the constraint. So, the upper the lowest value would be minus of I R L, but the absolute limit would be minus V cc plus V c sat. Now, so we have these equations here which we talked about. Now, let us look at let us have a look at the output signal waveforms of this particular transistor stage we saw now. Now, what we can say is that if you can choose the bias current I properly then the output voltage V o can swing from approximately minus V cc to plus V cc and the equation value would be V out is equal to 0. Now, we can kind of sketch say 2 3 waveforms 1 waveform would be we would like to see the kind of V c 1 waveform when you apply a signal we want to see how the V c 1 signal varies. So, we know that since the V c 1 since we are talking about a common collector stage and the output is at the emitter. So, therefore V c 1 is nothing but V cc minus V out because V out is same as V e and V c is nothing but V cc. So, V c 1 is nothing but V cc minus V out. Now, we can also kind of sketch another waveform which would tell us the value of I. Now, we can also kind of sketch the instantaneous power dissipation which is defined as V c 1 times I c 1. So, if you look at these waveforms what we see here the first one is the V out waveform and we said that we would assume that it goes from the two extremes. So, this is the kind of maximum possibility on the positive side approximately it can go to plus V cc or the negative side it can say approximately go to minus V cc. So, that is the V out signal. Now, corresponding to that if you look at the V c 1 we wrote the equation there as V c 1 is equal to V cc minus V out. So, if you do that we see that this is if you substitute our V out there and we see that as far as V c 1 is concerned the it can go from all the way from if you go to the extremes we would see that it can go from 0 all the way to 2 V cc with a kind of a fission value being V cc. So, when V out is 0 we have V cc, but with signal the V c 1 changes all the way it can vary from 0 all the way to twice V cc. So, that is as far as the V c 1 waveform is concerned. Now, if you look at the I c 1 the current flowing through the top transistor if you think about that I c 1 current there now the equation value is I. So, when there is no signal it is I now with signal it can go up on the positive side all the way to twice I on the negative side it can go all the way to 0. So, that is the excursion of the collector current and we are just at the border of class A. Now, what we have here on the last waveform is the power dissipation the instantaneous power dissipation which is p d 1 which we see is have a very interesting waveform. Now, the equation value of current was I and the equation value of V c 1 was V cc. So, when there is no signal the power dissipation is V cc times I, but with signal we see that the power dissipation varies. So, what we see here is something very interesting which is very very very different and this is one of the reasons why we do not like to have a class A amplifier. So, from this particular waveform we see that this is a very important sketch. So, this particular one what is telling this is about the power dissipation of that transistor which is q 1. Now, what it says is that you have a maximum dissipation when there is no signal. So, if you have no signal then you are going to have the maximum dissipation. So, that is something very strange when we are not using it the the V j t is getting heated up the maximum with signal the power dissipation changes. So, this tells us gives us a clue about its efficiency. Now, let us work out some numbers write some expressions for the power conversion efficiency of a class A amplifier.  Now, in our example we had two power supplies.  So, p l by p s is what we would define as efficiency because this would directly tell us about the power conversion efficiency.  So, this would give us the RMS value. So, V o m divide by root to the whole square divide by R l which is nothing but half of V o m square by R l. So, this tells us the power supplied to the load. Now, the power drawn from the power supply is we can find out from the p d 1 which we said is V c 1 I c 1. Now, we know that the and that particular. So, the power conversion efficiency we can see as by substituting we would see that this would be one-fourth of V o m square divide by I R l V c c. Now, we know that the maximum which we can allow the output cannot rise more than V c c or it cannot it has to be within I R l. Therefore, the maximum efficiency we can get here is for the condition when the V o max is equal to V c c is equal to I R l and for that condition the maximum efficiency possible is 25 percent. So, this gives us an extremely important result as far as class a amplifier is concerned. So, for a class a amplifier the maximum theoretically possible efficiency is 25 percent. And we know that even this we said is an approximation the signal input signal cannot approach V c c we assumed it to be V c c. So, therefore, we said it is 25 percent. So, most of the time when you talk about a class a output stage you cannot operate at that kind of input level. So, typically the kind of efficiency you actually get in a normal operation is somewhere between say 10 to 20 percent because most of the time your output swing would be definitely the peak of the output thing would be less than V c c. So, we see one something which is extremely important to remember that is class a amplifier even though it gives us the least distortion because it conducts throughout is the least efficient. And we said an extremely important consideration it was not a consideration when we talked about small signal amplifiers because the powers where we are talking about there were in a few milliwatts. And the device getting heated up was not an issue at all because the collector currents typically we talked about where a few milliamps are the most. And we never ever had a problem of power dissipation, but here we are talking about several watts several tens of watts or in some cases let us say hundreds of watts we are talking about a publicator system we are talking about at least 100 watts or if you are talking about a major a publicator system we are talking about thousands of watts. So, efficiency is one of the most important consideration. So, therefore, we can conclude that for an output stage we should never ever use a class a amplifier unless otherwise our power requirement is extremely small. If our power requirement let us say is less than a watt then class a is the best choice, but if our power requirement is more than a watt or if you are let us say several watts then definitely we should not go for a class a stage. Now, let us look at the next class of circuit which is actually a class b amplifier. Now, in a class c class b amplifier we as we discussed right in the beginning since it conducts only for 180 degrees we have to use two stages. Now, what we have here is basically a complementary pair of transistors an n p n and a p n b. So, the top transistor we have an n p n transistor and the bottom transistor we have a p n p. So, it is used in a complementary fashion. Now, we can see from the signal here that when your input is positive the upper device the q n the p n p the n p n transistor will conduct when the input is negative the p n p transistor will conduct. So, we the way is connected we know that both of them cannot conduct in the same time simultaneously they cannot conduct. When you talk about a class b this is what we talk about ideally what we expect is that the top transistor would take care of the positive half cycle and the bottom transistor will take care of the negative half cycle. Now, let us look at the circuit operation in detail. Now, when the input is 0 so let us have a look at it. Now, when the input the voltage is 0 what we can say is that both of them are off. Now, as you keep increasing V i on the positive side we know that this particular V B you need at least 0.5 volts. So, till V i equals 0.5 q n cannot conduct once V i exceeds say about 0.5 this particular voltage may not be exactly 0.5, but somewhere around that we know that once it exceeds that say about 0.5 volts the q n would start conducting and the current now would start flowing into the load. Now, during the entire positive half cycle the q p device the bottom p n p device would be off. Now, coming into the negative half cycle when V i again when V i is equal to 0 we know that both of them are off because there is not enough forward bias when V i goes negative and the V e b or the V b e when it is less than minus 0.5 when V b e is less than minus 0.5 the p n p transistor would conduct till then it cannot conduct and beyond that point the p n p would conduct and you would have a current flowing into the load. Now, so this is what we discussed when V i is equal to 0 both are off when V i is positive and it crosses about 0.5 volt q n conducts. So, beyond 0.5 volt we can say the transistor the upper transistor the the the n p n transistor works like a emitter follower and we can say that V out is equal to V i minus V b n this n stands for that n p n V b value of the n p n transistor and during this p the q p the p n p transistor will be off as as long as V i is greater than 0. When V i is less than 0 and when it goes below minus 0.5 q p turns on and this now acts as a emitter follower the output voltage V out in this case we can write as V i plus V b e p mind you in a p n p transistor the emitter would be more positive. So, whereas in a n p n transistor the emitter would be less positive compared to the base. So, hence this changes now q n will be off for the entire duration when the input voltage is less than 0. Now, let us sketch what we talked about let us sketch it into a transfer characteristic. Now, this characteristic is extremely important this particular graph as a lot of significance in the design of a power amplifier. Now, what we have here is what we just said in words. So, on the positive what we have is V i on the x axis V out the output of the amplifier on the y axis and we said that when it is 0 both are off no current flows. Now, till about 0.5 volts the output is 0 once the input goes above plus 0.5 the current starts flowing the n p n transistor contacts and the current starts flowing and then you have an emitter follower and you have a slope of unity slope and then at the upper end we know that it cannot go beyond V c c minus V c sat because the it will go into saturation. So, that is the upper limit coming to the negative side we see that once the n p transistor can contact only when the input goes below minus 0.5 and once the input is below minus 0.5 you have an emitter follower again in action and the slope will be unity and again the you have a negative limit there would be minus V c c plus V c p sat this p stands for the p n p a saturation voltage of the p n p transistor. Now, having seen this so we somebody might wonder why if this and it is obvious seeing from the transfer characteristic that we are definitely going to get a distorted output, but then why are we interested in class B that will be very clear once we see the power conversion efficiency calculations of a class B amplifier. Now, a class B power amplifier once again we can write the same equations which we did for class A the average power we wrote there of the output sinusoid with a p amplitude V o m is P L equals half V o m square by R L. Now, the current drawn from the power supplies will be half sinusoids because we know that each of those transistors conduct only for half cycle and when the n p n transistor conducts the power is drawn from the positive supply when the n p n when the p n p transistor conducts the power is drawn from the negative power supply. So, we have current drawn about half sinusoids drawn from the power supplies and the peak amplitude there will be V o m which is the maximum value by R L that is the peak current drawn. Now, the average power drawn from the power supplies we can write as p s plus stands for the positive power supply equals p s minus which is the power drawn from the negative power supply and that will be 1 by pi V o by R L into V c c. Now, so the total power supplied we could that will be double of that. So, the total power supplied will be twice V o m V c c divided by pi R L. So, now we can write an expression for the power conversion efficiency. So, if you do the substitution we would get this expression we will see eta the power conversion efficiency as p l by p s as half V o m square by R L which is the power delivered to the load divided by the power supplied which is 2 by pi times V o m into V c c by R L. Now, this we would get it to be pi by 4 into V o m by V c c. Now, eta max happens when we have V o m equal to V c c. Now, that gives us 75 78.5 this is an extremely large number compare this with the class A amplifier. With the class A power amplifier we said the maximum possible was 25 percent. Now, there is a lot of difference between 25 percent and 78.5 percent extremely large difference. So, now we are very clear why we are interested in class B amplifier. We see that the interest in class B amplifier is primarily from the point of view of the efficiency. Now, what we have here is a plot of that equation which we just now wrote there with V o m rather V maximum on the x axis and the power dissipation on the y axis. Now, mind you the power dissipation would be the power supplied minus power delivered. So, whatever power you supply and the whatever if you subtract the power delivered to the load and the remaining power is dissipated in the device. So, we would see that in a class B amplifier the power dissipation would keep increasing as you keep increasing the input voltage. Now, it reaches a peak and the peak power dissipation is actually twice V c c square by pi square R L there and at that particular point the efficiency is only 50 percent, but even that is very high compared to a class A output stage. Now, this happens when the input signal is twice V c c by pi. So, that gives us the max the value of the input signal at which we get maximum power dissipation. Now, the point at which we get maximum efficiency is at that we saw that is the point at which where our maximum the V maximum is same as the V c c at that particular point we have an efficiency of 78.5 percent. Now, this gives us a very very good reason why we should go for class B. So, class B power output amplifiers or the output stages are very good from the point of your power conversion efficiency and 78 percent is not at all bad is extremely good. Now, unfortunately there is a problem this we saw from the transfer characteristics we saw that in the transfer characteristics we had a dead zone, dead zone meaning we had a region there that region was plus minus 5 when the V i is within plus minus 0.5 volts we saw that during that period we had a dead zone meaning we have no output. So, because of this we would have what is called crossover distortion. Now, crossover distortion is extremely disturbing it is a very I would suggest it is a very very good idea to design a very simple inter follower like the one which we have done maybe some little biasing changes can be there and you would see that if you apply a signal you could then apply you could just maybe speak into one such class B amplifiers and you can listen to the sound from a loud speaker and then you will understand what you mean by crossover distortion. Now, the crossover distortion would be extremely disturbing this is because of the reason that our ear is extremely sensitive it can pick up even the smallest distortion and again that is people dependent some people are much more sensitive than others, but crossover distortion is easily distinguishable. So, if you give a signal especially a voice signal maybe a music signal you put it through a class B amplifier and then you put it to a speaker it will be very evident what is crossover distortion the sound would be very displacing. So, we need to find so class B is very good from the point of view of efficiency, but it is very bad from the point of view of crossover distortion. So, we need to find a middle path we need to find a way of reducing the crossover distortion without sacrificing much on the efficiency. Now, this is where the next class of amplifier comes into picture and class AB amplifier is the amplifier which is actually used in practice. So, as we discussed so far class A amplifier we also discuss class B amplifiers both these amplifiers are actually done only for the sake of theoretical analysis. And we from our discussion so far we saw that both of them are bad from the point of view of an actual application and the problem with a class A amplifier was the class A amplifier was very good on the point of view of distortion it had it had no distortion because it conducted for throughout the period, but we saw that a class A amplifier unfortunately has only 25 percent efficiency while a class B amplifier we saw that was very efficient we could we could get a maximum efficiency of 78.5 percent but unfortunately because of the dead zone which we have in the transfer characteristic we have a what is called a crossover distortion which is displacing and which we cannot have. Now, in a class AB amplifier as the name itself suggest is kind of a let us say a mix of both class A and class B. In a class A we have the conduction throughout the period of the sine wave in a class B you had a conduction only half cycle. So, in a class AB you would have a conduction which is greater than 180 degrees, but that is less than 360 degrees. Now, let us have a kind of a look at say a kind of a conceptual diagram where we have what we have done is. So, you could see the signal being applied to the base here. Now, the difference between this particular circuit and the circuit of the class B amplifier was the case of a class B amplifier we did not have this small biasing here. Here we have introduced a small battery called VBB by 2 and we here also. So, both the transistors we have introduced a small battery here. Now, the purpose of this particular battery is to ensure that when there is no signal when V i is equal to 0 we would like the NPN transistor to be just at the threshold of conduction. Because if we have if we adjust that voltage on the higher side then the transistor would conduct then we will get into class A situation throughout. If you make it too small then what will happen is it will it will have distortion. So, this particular voltage need to be very very carefully chosen. So, let us tentatively take this value of this voltage to be 0.5 volts, but this is a voltage which we need to choose very carefully. Now, again it is not a bad idea if we have one of those old transistor radios with you a portable transistor radio. Most of this radio sets would have an adjustment for this cross out distortion. If you look at any kind of a portable application like a tape recorder or a radio all of them would use a class A B. And what is done is in kind of a cheap portable application this voltage adjustment of this voltage is very difficult. So, what is actually done is you would actually apply a signal you would listen because this is a you have a loudspeaker there. So, you would listen to the sound and then you would have a kind of a potential meter arrangement which would give you some voltage. So, what is done is you would slowly adjust the voltage in such a way that and what is generally done a symmetrical kind of arrangement is done. So, that the kind of a positive of that supply negative of that applies here or you can even think of two separate parts. So, what is done is you would apply voltage in such a way that you are just at the threshold that the distortion just disappears. In fact occasionally what people do to do this is to connect an ammeter in the VCC path. Now, if it is class B no current will be drawn from VCC when you apply no signal here. Now, as you keep a keep changing this VBB voltage here if as you go from say slightly conducting to more conduction huge amount of current will flow here. So, that is how this current this particular biasing is done, but we will not worry about it. So, let us assume that we know this particular value and we have applied that conductor voltage here. So, what now happens is when you apply a signal here the output now is going to be V i plus we would have this particular bias kind of adjusted here. So, what we would get is the just the output would then we would get rid of this particular the distortion there. So, the dead sound would disappear in this particular case of the PNB transistor we have the base being brought negative. So, we could see from here that through since the emitters of both the transistor connected together we need to ensure that this potential is less by VBB by 2. So, this is how we would implement a class AB amplifier. Now, once we do this we can see that we get a linear characteristics ideally and as I said rightly you need to choose this particular voltage very carefully and that is when we actually design a class AB amplifier you would see that this is one of the most challenging jobs or one of the most difficult part of because if you go from say no conduction to conduction you need to ensure that you do not drain the supply too much because if you have too much current flowing you are playing with the efficiency and the efficiency will drastically come down. Now, what we have here is a kind of a typical biasing of class AB amplifier which is typically used for kind of an IC kind of an application this is the way you would bias and you could also do this with kind of diodes. These days you would get in fact in fact what we get occasionally you would get some of these matched diodes or transistors in kind of arrays which could be used for this purpose, but this kind of biasing is easily done in an IC. So, what is done here is you would first decide what is the voltage you need here to ensure that it is just at the threshold and accordingly you would choose a current bias current. Now, we know that V that VB voltage V is related to the current bias current by the equation VT ln i by is. So, by adjusting this value of i by s to the decide value we could get whatever is the decide value of VB here. So, essentially what we are doing here now here is we are ensuring that this particular one is you have two VB between these two bases that would ensure that the if it is properly biased we can ensure that if we are adjust at the threshold of conduction and that would ensure that we have fairly large efficiency, but not as large as 78 percent, but the same time not as small as 25 percent. So, depending on the biasing here we would be able to get different kind of efficiency. So, far we studied we as of now we discussed class A amplifier we also talked about class B amplifiers we also talked about class AB and we saw why class AB amplifier was required here.


We think that men who do not have access to money or stability, or security, or confidence, or conversation skills don't deserve to have sex. It's an evolution thing. You shouldn't, you don't deserve it. You... Well, yeah, I would agree. No one deserves to have someone else's body. Right, I mean, but okay, a man without money. Are you saying broken, secure dudes should not have sex? I think that... What do you think of the new look that we've got? We are trying to step up our presentation and production this year. And if you are too, I'm proud to share this video sponsored by Squarespace, a place where you could build the perfect website, start email campaigns, or open an online store today. When you build a community on social media, it's someone else's algorithm, taste, and rules that govern how you can connect with your people. With Squarespace, you're in the driver's seat and you have the power to customize your content to fit your brand and your needs. My website, my mailing list, my book website, all of them are powered with Squarespace. And if you are ready to try and see if they can power your next big idea, go to squarespace.com slash shambudi to start playing around for absolute free, no credit card required. And then when you're ready to launch, you get 10% off your first purchase of a website or a domain. Once again, it's squarespace.com slash shambudi. All right, from your understanding, what is the proposed sex strike? Anybody wanna explain it? Do we know why we're here?   But then I was like, if men want sex, they're gonna get sex in some way, shape, or form.  I know for me, anytime I'm intimate with a situation ship or casual sex or whatever, I lose my mind a little bit. And I can't focus on work, my art is awful and I'm just kind of like losing my mind. So I abstain from sex just to like re-center myself. And I think if I were ever to go on a strike, it would be for myself and not to like affect men. Because I realize no matter what I do, I cannot control a man ever. That's interesting.  And so in order to make the stock go up, you have to create scarcity. So I think that the concept is generally like, it has to be all or nothing. Like we're all in this together and unifying to be like, we are going to hoard the stock. I agree.  I think that as a result of it being so saturated, it's caused a level of entitlement to men and feeling like they can always just get what they want out of women. And if you're not going to give it to them, they'll get it somewhere else. And it's causing issues in dating and mating and long-term partnership and managing expectations and what could occur in a relationship and what's respectable in a relationship because there's too much pussy out there that they feel like they should have access to because not that we've made it that way, but because of the way that media has evolved within the last 10 to 20 years. My mind went kind of the opposite of what you initially thought. Like at first I think I just went for like, well, I mean, sure, if a man's bad at sex, I don't want to have sex with him. Like if we're not getting taken care of, we should like pull back. I think regardless of what reason you're talking about, I think what my mind has been going to as I've been thinking about it is like the idea of a sex strike and taking sex away from men, whether it's based on performance or abortion or whatever, I think it puts sex in this place of almost like it's a reward for men.  So to put it in a place of like, I'm taking this away from you so you can't have it.  So I think again, whether it's based on like performance, like, oh, like he was not meeting my needs, whether it is a political stance, like I think it's all valid, but it's more like, I think what you were talking about is like, I think it should be a self-choice. It takes two to tango, I don't think it should, it makes it about them. And I think that's already such a problem with sex is it's like too much about men. I think that limiting yourself in any way, one way or the other, would be doing yourself a disservice.  And I think if we're gonna talk about it in the context of abortion or laws or what's going on in society, if it being too available through Instagram and where our society is gone, often the law and politics in society can be very behind what we want it to be. So we have the opportunity to get to know our bodies in a deeper way. We have an opportunity to get to know our rights and we have an opportunity to figure out what do we want to change and how can we start doing that through practice before we let the law and society catch up with us. Women, y'all grant access to sex. So if you wanna have a serious relationship, you're trying to build something with somebody and you're not giving them sex, they can get it somewhere else. And I feel like that's the little bit of the issue where women aren't necessarily on the same page overall. You don't have to be. Everybody has free will to do what they want, but if sex is so available, it's given to so many people, it makes me quick to go, if I'm trying to date you and after like a week or two, you're not giving it up and it's like, I know somebody that will, just so easily and require less. I think it's a thing that people don't realize that all men don't have sex. All men don't have sex. Majority of men can't get sex. The problem is the small group of men are getting all the sex. I think if there would be a sex strike, it might need to maybe be a, I don't know if you wanna pull a preference or maybe a pullback from all of us giving sex to the same men at such a large rate because I have friends that haven't had sex in months and then I can talk to my one homeboy, he can have sex three times a day if he wanted to. So I think that's just the balance there where I think a lot of people have a misconception where men are just having sex all the time. The average man can have sex when he wants. It's just not possible. Well, you're referencing that 2019 stat that came out that said that one in three men under 30 have not had sex at all in the last year. And so this idea that men have constant sexual access to your point, it's some have. So is there something to shifting the landscape so it's more in women's favor where we make the sexual culture less libertine? Like that's what it's about. It comes down to power. And do you feel like you have the power right now in dating landscape? I personally believe that my vagina deserves the absolute best in men from courting to intimacy, to foreplay, to consistency. And so I- Ooh, I love consistency. I'm not engaging with anyone who's not showing me those qualities and probably more that I forgot to mention sexually. And because I'm not willing to partake in half ass engagements with men in pursuit of sex, I am completely kind of like waving the flag and okay with masturbating because I don't want to deal with what I feel like is in the market right now. So I don't feel like I'm in power, essentially. But that's almost a form of power. Like that exact reason, because I have the same thoughts about myself, is why I feel like I am in control because I used to kind of just take what I can get and that kind of derailed me emotionally in every aspect of my life. And because I've kind of honed it in a little and know what I deserve, I think I feel like I'm more in control.  Yeah. Oh yeah. Yeah. You're open with that. Oh yeah. Who here is on a sex strike right now? In the context of how you positioned the question in terms of the dating pool, yes I do feel empowered that I've like, know my self-respect and my values and blah, blah, blah, all of that. But, you know. But a strike that is not unified is useless. Exactly. Like that's the whole point of a strike. The behaviors are not being, it's not influencing men to be better. What's the term when somebody, you cross the picketing line, right? What's the term when, you know what I mean?   Right. Right? But there's no way for all of us. Well, you want a disproportionate amount. Yes. The book that's called Data Nomics that I read that basically talked about this wherein that when the sexual market is more libertine, like sex is more accessible, it puts women in a disadvantage when it comes to long-term relationships. But when it comes to great sex, maybe they're in an advantage. So that's kind of how you look at it. And that's why I think I struggled to answer the question because like, like to your point, I think when I think about like serious dating, what I want in like a lifelong partner, like, no, I'm not doing very well these days. Like I'm not finding that. If I wanted to just go out and have casual sex, like I could grab my phone right now and probably find that. So like, I think, do I feel empowered that I could go find some sexual gratification, hook up with someone if I wanted to? Yes, I think that is easily accessible. Am I easily finding like the serious partner that I want these days? No. And so, but I think that also comes down to like what people want. Like if someone was just in the mood for something casual, like it's easy to find it here. And that probably would feel empowering. Like, hey, this is what I'm looking for and I can go find it. That's great. But like if you are looking for something more serious, I think, yeah, a mix of like these statistics, just kind of our current culture, it does, I think for women, I think, yeah, it is more difficult to find kind of that serious and all the things that you want in a partner. Can I challenge that thought too? Because I feel like even the casual, you know, hook up culture is not of quality anymore. Oh no, no. Like I feel like, you know, you can casually and like, you know, with integrity have a relations with a man that still feels respectable. Whereas now I feel like we've hit a crisis and like because of dating apps, you know, some men look at women as like pure wet boxes. And there's no integrity in terms of pursuing a respectable casual relationship with that one. So I feel like if women can collectively think that, okay, this has hit a crisis level and we don't want to participate in being treated like wet boxes, and we decide to stop, then I think things can change. If y'all get on the same accord, men will change. If you think about the nineties and the music men would make, we had to sing in serenade y'all to even get a chance. We would have to beg for y'all. We still do. Some of that. No, no, no, no, seriously. Like you listen, and I'm a DJ, so you know, a lot of things, a lot of my references are through music, but and if we lose you, we'll scream and cry for you back, but with this, and I don't want to put it on the city girls, but the city girl era, yes, there's a lot of sexual empowerment, but it kind of leaves those people out that wants like those serious things out to drive because everybody's not living that lifestyle. Some people do want something serious and it's like, well, I want something serious, but the next three girls over are like, no, I don't care, and I require less, and I'll give it to the same guy that you might want to have something serious with. So the dating pool is kind of like rocky, and as a guy that might be in that position where I can have the pick of the litter, it's like, why would I put up with all your standards and requirements when old girl who looks just as good, might be just as accomplished, has a different mindset that benefits what I want right now.  Like they weren't coming, they weren't getting it. Like there was, when I first started as a sex educator in 2005, the orgasm gap was three to one.  The orgasm gap is now two to one. That's a huge drastic decrease that's happened, and I think we have the sexual liberation movement to thank for that. So maybe the quality of relationships is more difficult to find, but good quality sex, I think, is easier and more consistent than it used to be. Well, because everyone's sharing the same guy.  That's what I'm saying. If you got one dude you find and knows how to put it down, we all can share him. The one guy that I've been hooking up with the last year in the city, I'm like now friends with all of the girls somehow. Like a sister-wives thing. Basically. So. But I'm saying that's how you close the gap. It's like, okay, I used to have to stay with my one husband or whoever that probably didn't do it. Now it's like, I know he got it good. That's all I care about. And he's serving the community. I also feel like though with that, the men who know they can get whatever they want, whoever they want are the ones who put in the least effort though.   And you're gonna think it's cool that you were with them. And for some girls that's probably great. I know for me at this point, I don't care who you are, I'd rather have a good experience. But I don't know. So yeah, I'm sure there's guys getting it, but I doubt. If you interview those women, I doubt they're as satisfied. It's not the dude reading the comma sutra who's been to that class who has that one cool uncle who's having sex with everybody.  I don't know what. I think the man I'm talking about is so like in tune with women and so. I mean, I feel like I'm having a very unique experience with them. But apparently everyone's having a very unique experience with them. But hey, I met some cool friends. The more educated and higher status a woman becomes, she has less options. And the man is the reverse. Right. And so I think that's why I found as I've gotten older, I too. Like you guys have just not been interested in as many men or I've found myself much more picky. So inadvertently, I have gone on a strike. Same.  I enjoy sex as much as any human does. It's about, again, the quality of the interaction, the thoughtfulness, the respect, you know, the quality of the sex. You know, again, if you're being treated like a depository with no, nothing to look forward to towards the future or even like, even if it's gonna be just that one time in New York, you know what I mean? It doesn't make it worth it.  But again, the quality of that hookup is not going to be valuable for me to want to do it again versus a man that I talked at a bar and like, I liked his mind and then I want to like, you know, get on my demon time with him because I'm attracted to his mind, you know? Can I propose a solution? I think I can fix this. Work with me here. So there are two thirds of straight men who have not had sexual part in the past year who are very eager to please and looking to do that.  So we have a strike with the minority of men who are having all of the women and then the men who are not getting much, we use them for sexual pleasure and satisfaction. But why are they not getting much? Y'all don't even see them kind of men. They're all past them every day. That's why. That's true. I just don't see that every man's gonna murder me so that's why I just don't even... Let's not even talk about that. Like, but why not compartmentalization? Could that be the key here? Where who are these men who are not having sex? People who are. Okay, so you describe, the problem you described is as women get further along in life in terms of education and earning power, they look for partners who are equal or greater. Men, as they get further along, they get more access to people, but they're not looking up, they're looking down. They're willing to date somebody who works at Chipotle or somebody who owns Disney. So they have both directions going for themselves. So our access gets less because we're only going and looking in this direction. But if you looked down, lack of better term, I don't wanna say the word down, but if you looked to the Chipotle worker for sexual satisfaction, but maybe only looked to people who were gonna give you that sapeous sexual experience for something more long-term, and then withheld sex from them across the board, but then gave the Chipotle guy some really good. Like, does that not mathematical, is the math not it? Don't do Chipotle, because it's guys that work in construction that own construction companies, it's plumbers, electricians. Firefighters. Firefighters. There's so many companies. Firefighters are getting pussy. Let's not add them. No, no, no, no, no, no, no, no, no, no, no, no, no. Let's not add them to the fight. This is the problem.  Every man is not.  One of them guys probably is. He's probably getting all the pussy.  Anthony, are you getting pussy? I'm married to him. I mean, I was wondering- It's a hard concept for them to get. It's like, yo, all dudes are not getting it. But I do think that we know who is and who isn't. I don't think it is. It's the person you least expect. I don't know if there's a lot of truth to that. I think it's not that you don't know. I think the guys that you don't know, you don't even see them. You don't even- Who are you referring to? The Chipotle workers are getting pussy, I think. Who are you referring to? But that's what I'm saying. Who's not this? It's not necessarily- Yeah, who is not getting pussy according to you? But it's not necessarily an economic or job thing.  Who are they? What do you mean? You want to name people? Are they hiding? No, what do you mean like that? No, they're outside.  You don't even realize them because maybe they're not attractive to you. Like you don't even see them. But these are everyday guys. These are my friends. I'm sure you have friends like this. And they don't talk about it like, yo, Brian, getting on, but you just know. It's like, I've never seen him with anybody. I wonder one thing too. I don't know what the statistics are on this, but like, I feel like the men who aren't having sex, obviously not all, but I wonder how many of them aren't having sex but would like to be having sex. Whereas I feel like most women, I know my own self, like I'm not intimate with people these days out of choice. Like, I just don't want to, am I right? I don't want to! But it's like, you know, for personal reasons, like I'm kind of, I've kind of walked away from that for a little bit, but I wonder how many of those statistics, those men who aren't having sex, like, is it because they don't want to or like, are they not getting it, you know? They can't. And I think what happens is, and it's hard to not, like I think women look at it as like, we have the same opportunities.   I'm trying to use a woman. Some guys want relationships, want to actually build with a girl and they just, they might be awkward, it might be whatever it is, it's just, they don't have that. Or they're going dates and the girl's like, oh, okay, this was a fun two dates and they get ghosted. Like, men get ghosted too. I ghosted when I was 12. That's where I learned ghosting from. It's never recovered. Yeah. I'm still bringing it up. I think, okay, and this is, you know, maybe not the topic, but I personally think that men who do not have access to money or stability or security or confidence or conversation skills don't deserve to have sex. It's an evolution thing. You shouldn't, you don't deserve it. You, Well, yeah, I would agree. No one deserves to have someone else's body. I mean, but okay, a man without money. Are you saying broken secure dudes should not have sex? I think that you're, if you're broken insecure, you have bigger issues to fix. You need to focus on that, not think that you are deserving of a partner sexually or long-term. You know what I think we need? We need a part two for this for sure. Content like this is only possible with the support of Squarespace. So big shout out to them for partnering with us for a number of years now. Now you can also partner with Squarespace to power your next big idea by buying a domain, building a website, starting or transferring your mailing list, opening an online store, creating paid subscription communities, and so much more. Improve your workflow, integrate your social media, blog and have access to in-depth analytics to understand who your people are all with the help of Squarespace. Right now, Squarespace is offering a two week free trial plus 10% off the purchase of a website or a domain should you choose to launch with them. To get in on this deal, all you have to do is go to Squarespace.com slash Shambudi. Again, that's Squarespace.com slash Shambudi and here's what we have coming up on our next video with them.  Like, I don't have to do anything. I can get away with murder because I got that good pussy. That's... Disagree? I only disagree because men are stupid, right? I know personally women that have been pillow princesses or tried to be pillow princesses with me and I could just be like, I don't care how good you look. If you don't throw it back, we could just end this right here because I know what I'm about to bring and I don't care if I look good, I'm smelling great, I'm feeling myself. I'm gonna still bring the energy with my physical attraction. I mean, yeah, I've been able to get away with it a lot.


So our agenda at Facebook at Davos this year is really two things which is connectivity and jobs. As we think about the fact that only 40% of people in the world are currently connected to data, we see so much more opportunity for people to get more voice, for people to get more access, for economic opportunity, and importantly for equality.


In this video, we'll look at characteristic chemical reactions that mark out acids. So let's begin by revising our comparison of the properties of acids and bases. Acids taste sour, whereas bases taste bitter. Acid base indicators will change colour depending on which type of chemical they come into contact with, the classic example being litmus, which turns red in an acid and blue in a base. Acids and bases also, if they're mixed, neutralise each other's properties and they can corrode materials, although the chemical reactions that occur during the corrosion are different for acids and bases. So we're going to look specifically at some of these characteristic reactions that acids undergo. So here are those reactions. I've written them out here in a generic form. I'm not going to specify what acid or what base or what metal or what carbonate at this point. The point is that as long as you know what class of substance is reacting, the reaction will always follow the same general form. The neat thing about this is that once you choose what your reactants are going to be, you can predict what the products of the reactions will be. So these are our reactions. Let me introduce them to you first, and then I'll go through and give examples. The first is dissociation. Here an acid molecule that's dissolved in water splits up, and when it does so, the result is one or more protons and whatever the remaining anion is. Remember that the protons or hydrogen ions can also join up with water to form hydronium ions. The next is a neutralisation reaction. When an acid reacts with a base, the result is a salt, an ionic compound and water. The next two reactions are kinds of corrosion. When an acid reacts with a metal, the metal is eaten away and the products are a salt and hydrogen gas. When an acid reacts with a carbonate, the carbonate is eaten away and a salt and carbon dioxide gas and water are produced. Before I go into examples, I just want to remind you of Bronsted's and Lowry's definitions of acids and bases, because we'll look at each of the reaction examples in the context of these definitions. Remember that an acid is a chemical that when it reacts, it donates a proton or a hydrogen ion to something else. That is, it will lose a proton itself. Bases are the opposite, something that accepts a proton during a chemical reaction.


This week's IonMPI brought to you by, did you key need a fruit is from Maxim integrator? What is this week's IonMPI Lediator? This week's IonMPI is the Maxim Max 22530, which is a, sorry, it's a analog digital converter to four channel ADC, and it's an isolated ADC that also has like a built in DC-DC converter on chip, as well as five kilovolts isolation voltage. And so it solves a very particular problem, which I've actually seen where you want to measure power or data or signal or whatever or some monitoring in a system that has a lot of noise in it. It has motors or maybe it's floating or maybe it's, you know, the voltage is different than your earth voltage.  But this allows you just to isolate the analog data acquisition part. So it's actually, it's a wide SOIC, a SOIC-16, and I'll show you actually, because this is, this is like rendering that they've got is like a narrow one. But inside is a four channel ADC. And a lot of people, you know, when you have a microcontroller, you'll use the ADC in the microcontroller. So for example, you've got a, at Mega328 or you got a SAMD-21 or you've got an STM-32. Those have built in ADCs. And often those are, they're fairly good. They're 10-bit ADCs, maybe 12-bit. They can usually run about 100 kilosamples per second. If you are running something like a Raspberry Pi and you need an external ADC, you can use something like this, which is an I squared C, or there's also SPI ADCs that, you know, this one gives you four channels, input, cost a couple bucks. But like I said, these are not isolated. So you'll see at the bottom of this breakout to the left, it says like VDD, ground, and then SEL-SDA, you know, ALERT, whatever, A0, A1, A2, A3, you know, sometimes you'll have an A-Raf, you'll have a reference voltage, but that ground is the ground. Like the ground is a single ground, is the data ground, is the everything ground. There's only one ground line. If you look at the layout for the MAX 22530, you see on the right hand side there's the microcontroller and there's the SPI port where you can see like, you know, clock, data in, data out, and then interrupt, whatever.  So there's an inside, there's a galvanic isolator that connects between the left side, which is the analog input, and the right side, which is the data, the digital signal.  So those are two totally separate grounds, and then also the power supplies are totally separate. And what I really like about this ADC in particular is at the bottom, you can see it says like, micro power DC-DC, that's a DC-DC converter that's built in.  It's not a super powerful DC-DC converter, but it's just enough that you can do like the reference voltage and powering the ADC without having to have that separate supply. So it kind of takes care of a lot of stuff for you. It makes it really easy for you to do isolated ADC measurements. Um, for the isolation, it's got 500, sorry, 5000 volt RMS insulation rating. So, you know, you can definitely use this no matter what like medical or industrial purposes you've got. There's four channels so you can, you know, do four single channel or you can of course do differential if you need. And here's another thing that I thought was really neat.  So if you have like a bit flip in your SPI clock or like a glitch or it has CRC data.  There is an eval board available, which I picked up and actually this chip is in stock, which is amazing. And the eval board is kind of nice. It has a FT-2232 USB to serial, sorry, USB to SPI converter. So you plug it in, there's Windows software available that you can use to you know, read the data and set the registers and like Maxim does a very nice job where they kind of have everything available for you. So if you, you know, what I like about this is it's not like the fanciest sensor, it's not the, you know, the whatever a new mic controller with like Wi-Fi, but it does do one thing that does it really, really well. If you're doing an ADC and you need to, you know, measure a motor or an industrial situation or, you know, whatever, something where your your power supplies can't touch. You don't want to have a signal coming in, you know, from your loud, messy robot into your microcontroller. You can just use this and like it doesn't take any extra effort. You don't have to set up a separate, you know, isolated power supply. It kind of does it all and a good price too. And here's the best part. It's in stock. So it is. I have to pick my eye on MPIs in a way that you can get it. I will say, just so you know, the photo of this is incorrect. It's an SOIC chip, but it is in stock. Available Digikey. And there's a couple other versions that are available too. Like this, I think is the first one, the 22530. There's also the 22531 and the 22532. And those are, oh, hi, those are very similar. Thank you for, we had an exciting camera situation, but now we have a fixed camera. This is the, this is the chip. This is what it looks like. You can see it's kind of a thick. You'll notice that a lot of isolated chips use wide SOICs. And then there's a QR code you can use to download. Live while we were on video, the overhead that we use decided to die, right? I held it in my arms and it died. But that's okay. Nothing's going to stop us. Yeah, you could see it's just like no signal. But you can't stop the signal here. You can't stop IMPI. So while Lady Aida was showing this, I have another thing that I plugged in and it didn't destroy everything. So that is this week's IonMPI. Pick these up. You're just showing URL and nothing's going to stop us from doing IonMPI every week. So let me get us out of this and I'll show what happened. Okay. IonMPI.


If you haven't yet, make sure you subscribe to stay up to date with all the latest content we put out at this point We've pretty much got content going out every 24 to 48 hours. So make sure you subscribe to the channel So you don't stay stuck with your business Now if you want to get in contact with me to discuss your business right to talk about it I can show you some actionable steps You can take this week to to grow and scale if you want to do that and jump on a free 15 It's 20 minute call with me visit the description in this Video there'll be a calendar link. You can book a free 15 to 20 minute call with me If not, you can send me a direct a message To my email address, which is make money coaching sports at gmail.com I make your mission every single day to answer questions and Respond to coaches so today I want to talk about How to help your clients get recruited for college scholarships Now essentially what I'm going to talk about today is how you can as a business owner Create a college scholarship program Where you're helping The clients that you work with either one on one or in small groups get recruited for To play at college level. Okay. Now. This is something we have helped coaches in our program to to create But I want to be completely clear that if you are thinking of going down this this route And creating something similar in your business Right. The most important thing is that you need to have experience within this field Right. There's a lot of coaches that want to offer this as part of an extra An extra service within their business, but they've never had any results with with clients doing it. Okay, so you number one I would I would make sure that you're well connected within the College space so you have a lot of contacts with college coaches and number two make sure that you have experience getting actual clients recruited into colleges Okay, because it's very difficult All right, and also you're playing with the emotions of of the families you work with okay Because parents if they're going to pay a lot of money in your program, they expect you to get them results Okay, so make sure you're connected in the college space, right? You've got college contacts with coaches and also make sure you've got previous experience getting client's air recruited Right, so I'm going to share with you six pretty much six tips on how you can implement a college program into your into your training service, okay and Different ways that you can help your clients to get recruited now you can there's two ways you can go about it You can create an actual Program Which you work with a client specifically on this right? There's no training involved Right, you're specifically working and consulting with the client helping them to get recruited or Right, you can create a service where you're Training and you're doing the recruiting side. Okay, so there's some coaches that just do the consulting With us all they do there's other coaches that that create a program where there's training and There's a there's a college scholarship in there as well Okay, so essentially you're helping clients to get recruited into college Okay Now the first thing I would recommend if you want to start any any type of program like this You need to build a list of Your local colleges that you want to work with and you want to recommend to the clients you work with Okay, so what I would Recommend is I would start local So let's start locally with colleges in your city in your local area okay getting contact with them and Ask them what Types of players they're looking for what do they look for when they recruit they and build relationships with those local colleges. Okay, so that way any player or Athlete families that come to work with you. Okay, you can directly say to them, right? This is what this college is looking for. This is what this college is looking right? So you need to become an expert in this niche and in this field, right? The second one attend college ID camps and Showcases right so whatever sport you're in if it's in soccer if it's in basketball. Okay whatever sport is Right one thing you can do is you can help your clients to stay up-to-date with the latest college ID camps and college showcases Right, so the camps are essentially more Training okay, so They might be one day camps. They might be two day camps. They might be three day camps, right? It depends on the college But you as the expert you as the business owner need to be up-to-date with which are the latest College camps ID camps in the local area So that way you can recommend them to the clients you work with and you can push them towards Attending them and getting in front of college coaches. Okay now college showcases are a little bit more different. They're more The way I've seen it in the past is they're more Matches so players will attend playing 11v11 a game and then essentially coaches What they do is they they pick out the best players from from that match and then they'll get in contact with parents and And so forth. Okay, so the third one is reach out to college coaches yourself Okay, so the first one was build a list of local colleges Right now the third one is actually getting contact through to with the coaches at those colleges So best way to do it right number one. You can actually visit the college yourself right number two You can get in contact with them in through Platforms such as LinkedIn is a very common one Okay, essentially why you want to do this is because you want to build a relationship with those cut they've got those coaches that It gets to a point where those coaches can reach out to you and they ask you right Leo. I'm looking for a For a striker. I'm looking for a wing guard. Do can you recommend anyone to me? Hey College coaches are constantly looking to recruit players into their program And if they see you as an expert if they see you as someone that has a lot of influence Over over kids over clients in in that local area that local city Then they'll come to you and you can essentially set up a type of referral program where if you Get players into their program, right? You can get a referral fee either from the college itself or Through the parents by helping them to get recruited into the college Okay, so again if you need more help on this get in contact with me We have been doing this with coaches We've helped coaches to create really successful programs in all sports, right in soccer in football in basketball You know, whichever sport you you can think of we've worked with coaches and we've advised coaches on creating a similar program With their business right now the fourth one and this is something you can create separately Okay, there's some coaches that create an actual You know three six twelve month program, which is solely based on getting the Getting the athletes recruited to a college. There's other coaches that offer and highlight videos as an extra service So essentially the parent Comes to you and they pay you a fee Right, and you go out you you record them at the game That the the child is playing for for their team and then you edit the video to make it look Appealing to make it, you know, and it has all their specific highlights Strengths weaknesses so that you can send that video footage Back to the parent and then they can use it to send to upload on on their College air profile Okay, so that's an extra service you can You can offer parents, right? So highlight video editing Where parents essentially there's two ways you can do parents record the video and send it to you you edit it Or you can actually go out to to to watch your clients play Record the game and then edit it In your own time right this is a very common Service is a service that does take a lot of time right editing is not an easy process Takes a lot of time it takes a lot of effort a lot of energy Right, so it's a service that if you do really well, okay You can ultimately charge a premium for your service right and parents will pay if it's getting results and it looks really really good and Edited okay. Now the fifth one is creating an athlete social media account So this is again another service Some coaches offer so parents will come to coaches and say right I need my son to build my son or daughter. I want them to build a social media account where You know, we're reaching out to coaches through social media or it looks really really appealing and any college Coaches who you know come across their page Want to reach out to them to invite them into a college showcase? Etc. All right, so some coaches what they do is they offer this as a service as well So creating an athlete social media account where they upload a footage of the player Playing right they you know the player as well sends them Footage of them working out every single day, right? So essentially what you do is you create a journey through their social media account that Any college coach that comes across Can see what is the day today of this player? What are they like as a person? All right, what habits? How do they play in a in a game situation? Right and it's attractive. It's attractive to coaches and essentially if it's done really well it can get Interest from coaches, right? So this is this is something you can offer parents as well To create and manage their social media account so that you can As a coach you can send that social media account to college coaches and college coaches can then watch the journey of the player and If it's something that interests them right they can reach out to you and you can get you guys can schedule a meeting or schedule to send them to an ID camp or a showcase Etc. So get them in front of that college coach to hopefully then get get recruited to play at college right and Essentially the sixth one and this is this is not a strategy But it's more a recommendation is to make sure that you start the recruiting process early So as a business owner you don't want to promise parents and clients Something that then you're not going to deliver Okay, so essentially what you want to do is you want to make sure that any Any college Process that you're going through with your clients whatever you're helping them with whether it be highlight videos Whether it be getting them into ID camps or college showcases Creating highlight videos for them right or managing their social media You want to make sure that you start it early enough so that Okay, you you have enough time in order to get them recruited. Okay, because you can imagine For every one college Place there's probably going to be about 20 30 or 50 kids In that local area that want that college place right whatever sport it is So you have to make sure that you get in there early and you're doing the right things as a business owner Okay, and as a as a as a trainer to get your your client the best success possible Right now if you're leaving it last minute then the chances are You know some of the spots at those college programs will get taken up very quickly Okay, so you want to act quickly you want to start the process early so you have enough time to offer different types of service and Help your clients to get as much success as possible. All right, so if you need more help with this Okay, these are just five different ways that you can essentially get in front of Coaches and you can also offer your services To clients to parents to families so you can help their child to get recruited To play at college and essentially you can charge a fee in order to For helping them to achieve that goal. Okay, so essentially it was five But also the sixth was a recommendation, which is like I say to all coaches to start early Okay, you need any more help with this reach out to me two ways Go on to my calendar link book a call with me If not, then you can you can send me an email to make money coaching sports, right? Thank you for watching and I'll see you


Imagine you get sent day in and day out to a random company to work without pay. Each workday starts with an hour-long meeting followed by another meeting and another meeting and so on and so forth. All meetings are on different seemingly random corporate objectives, focus on X, improve Y, remember Z.  And when you think that the day is finally over, you are told to take some of the work home. Sounds like a horrific corporation, doesn't it? This, however, is the perceived reality of many young people in what's called a 21st century school. So how did we happen to end up here? Frederick the Great, the king of Prussia, came up with the idea of modern factory schools. The emperor was inspired by Plato, who argued that the ideal city requires ideal individuals and ideal individuals require an ideal education. And so the king introduced compulsory education in 1763 with the mission to unify Germany, increase literacy and boost the education of all its citizens, including the very poor. The early Prussian school system provided eight years of instruction in reading, writing, music and religious studies. It imposed a strict ethos of duty, discipline and obedience. And that worked. The model turned into a big cultural, economical and military success that inspired rulers from Tokyo to Washington. Not long after, state officials all around the world started writing curriculums, and public education became both a child's right and duty. In 1938, the Germans then went one step further and made school attendance compulsory, ever since it's not parents but the state that makes sure kids go to school. Today, 85% out of all adults worldwide are literate, and access to information is abundant. Should government officials still have a monopoly on how we learn? A growing number of parents don't think so and want to take control over their own child's education. They advocate for what's called unschooling. Unschooling is the process of learning through life, outside institutionalized classrooms. Similar to homeschooling, it usually happens at home or in other places. But while homeschooling usually follows a formal curriculum, unschooling doesn't. Unschoolers learn through their natural life experiences, including play, chores, travel, books, elective classes, board games, internships, mentors and living in a community. Parents or tutors play a big role. They provide resources, facilitate the learning experiences and help the child to reflect on their progress. So how come parents choose to unschool their children when it's much more convenient to send them to school? There are six key reasons. Schools can negatively affect the parent-child relationship, often replacing it with an atmosphere of fear. Institutionalizing kids in a one-size-fits-all classroom is an inefficient use of their time and potential because it requires each one to learn a subject in a particular way and at a pace that doesn't take into account a child's interests or any pre-existing knowledge they might have. In school, children are primarily taught how to follow instructions, which means they don't practice doing things independently. Unschoolers have to solve problems by themselves all the time. They learn to work autonomously. School children are told all their lives what to do. As a result, they later often have no idea what they want and hence simply conform. Unschoolers practice making their own decisions every day. They learn to know what they want and are more likely to question social ills. School focuses almost exclusively on what to learn all day. Unschoolers learn to ask the much more important question, why learn it? Schools cover only a few subjects someone thought of a few hundred years ago. Unschoolers can explore way more interests and look into topics at far greater depth. John Holt, a pioneer of unschooling, said it as follows. The anxiety children feel at constantly being tested, their fear of failure, punishment and disgrace severely reduces their ability both to perceive and to remember and drives them away from the material being studied into strategies for fooling teachers into thinking they know what they really don't know. What do you think? What are the good and bad sides of unschooling? And more broadly, should the state or parents decide what to teach a child and what to leave out? Who should have the ultimate say? Please share your thoughts in the comments below. If you like how we explain complicated ideas in simple cartoon animation, you can support us. Visit patreon.com slash sprouts. Just visit us, learn how it works and what's in it for you. We hope to see you there. And if you are a parent or educator, check out our website, sproutschools.com. There you can find this and other video lessons, additional resources and classroom activities. If you found this helpful, check out our other videos and subscribe. If you want to support our work, join us on patreon.com slash sprouts. For more information and additional content, visit sproutschools.com.