# mod05lec23

Welcome to this class there are several application of operational amplifier, that we have seen until now, and ah there are a lot of applications which which we can still ah ah use op amp for. ah We will see ah in today’s module ah ah very important application of an operation amplifier and that is ah voltage controlled current source voltage controlled current source So, what exactly voltage controlled current source means that, if you by changing the voltage by changing the voltage, you can change the current by changing the voltage you can have the ah you can design a current source And we will see seve[ral]- ah the current source voltage controlled current source, not only on the breadboard not only on the bread board, but also using multisim both the ways we will see and we will see the ah ah low low current application high current application So, on the breadboard probably we will see high current application, and on the multisim we will see a circuit which can be used for low current application. Now, when you talk about ah ah current source or or voltage controlled current source ah what as the what is the application of voltage controlled current source right, is there any other thing like ah constant current source, constant voltage source, if yes where are they used ah if it voltage controlled current source what is the application if it is a constant current source, what is the application constant voltage source, what is the application. So, try to understand as much as you can try to find it as much as you can all right So, for this particular module ah let us see what exactly voltage control current source is all right. So, if you come on the screen, you see that for many applications, for many applications one may have to convert a voltage signal to a proportional output current right is nothing, but V to i voltage to current converter right. So, hence a bipolar current generators may be required we need to require current. So, current generators are required these are called current sources these are called nothing, but current source all right A unipolar current generator or source is either a current source, or a current sink it can either source the current or it can sink the current right So, ah if it current source then it generates the out flowing current, if it sinks the current then generates the inflowing current right here, unipolar means that it can produce current flowing in one direction only usually towards the ground; that means, we see if you look at this particular circuit, if you look at this particular circuit. You know that the voltage there will be some voltage over here, which can be generated using a potentiometer, we can generator using potentiometer. Now, you know a concept of virtual ground, we have already seen what is virtual ground with the concept virtual ground, whatever voltages here same voltage would try to appear over here right, same voltage try to appear over here Now, what is this the circuit is nothing, but a voltage follower a voltage follower So, when this happens; that means, that the this transistor conducts and the resistor the current across this resistor the current across this resistor right, it it depends on the voltage that is we have applied over here, because trying to follow the same voltage depending on that if you have ah your emitter current here, then the same current would be there in the in the collector same current we will have in the collector. So, if I change this keep on changing this voltage I will constantly be able to see the change in the voltage across this resistor. And this change in resistor will keep my current constant, will be generate my current will keep my current across the load resistor flowing Because this transistor is in conducting state transistor will be in conducting state, one thing you have import[ant]- ah remember is the in the high power application, this particular resistor should be 10 watt 1 ohm, but we will see two different application of this ah voltage controlled current source one is in high power and they can easily low current applications low current applications all right. So, we will see two different circuits as well. ah First thing is now you understood how this circuit operates, then ah unipolar as we have discussed it is only that it will follow in from the source to the ground, it is has to go to ground. Now, voltage controlled current source or sink maybe designed using operational