Op Amps Characteristics Part 2 Internal Circuitry Op Amps and Op Amp Circuits Video Lecture

Op amps are composed of standard components such as—notice—transistors, resistors, diodes, and so forth, and a capacitor right here.

The input terminals of an op amp are connected to the bases of transistors. If we look at this, we'll see … Here we had the two input terminals. Here is the negative voltage and the positive voltage. This was pin six, the output, and then this was the offset, pins one and five go here. When we see an op amp, we just see the input pins; we don't see all of this circuitry and the details of what's going on in the circuitry goes well beyond an introductory course.

I do want to mention just a couple of things. You'll notice here if you look at this, this looks kind of like a differential amp here, when you had the two inputs, remember from the last chapter we looked at a differential amplifier? When they integrate components, something that happens is … For example, this component right here, though it looks like a transistor, and it is a transistor, it is doing the same job as a resistor.

This is actually the current regulator that feeds the current into the differential amplifier. The reason they do that is they found that they can make transistors much smaller than a resistor and so, in many cases, the transistors that you'll see in this circuit are actually acting as resistors.

Then I did want to point out the pins one and five, these were the offset values, and you'll notice that one is connected here and the other is connected here. What this is, this is the final output from the differential input and so you have the input coming in here and the input coming in here and, what is commonly done if these are used, a variable resistor can be placed across here and this is usually going to be external to the op amp and disconnected to these two pins and then if there is an offset voltage, that resistance can be varied so that the output voltage can be nulled out.

This is a simplified schematic diagram of what we just looked at. This makes it a little easier to comprehend. Remember, this would be that resistor that controls the current into the differential amplifier. These are the inverting and non-inverting inputs coming into the differential amp and then the output is fed over here. You may recognize this, this looks like the Darlington pair that we looked at in transistor circuits.

In this case, I should mention this also, this would be resistor controlling current, this is the dif amp, this would also be akin to the collector resistor that we looked at in the differential amp that develops the voltage. Then it's going to be fed here into the Darlington amp and from here there is actually a common emitter. This would be the common emitter transistor and this would be the resistor for the common emitter amp, so, again, we have another amplifier here. Then that is fed into a class B configuration and we haven't looked at that.

What's going to happen, as the signal is amplified, the positive signal will come out of Q9 and the negative will come out of Q10. The advantage of this kind of configuration is that the output here can be set for 0 V. Remember that we have the positive and the negative voltages in op amp, and so say we had +15 here and -15 here, the output, at least in theory, could swing from +15 to -15, this would make for a very large potential output.

Again, that is ideal. When we actually use these servers we wouldn't be able to go that, maybe would go to maybe 12-13 V maximum. At any rate, we're going to be able to maximize the output signal swing by use of this particular configuration.

If you're inclined to look at the actual components in the 741 op amp, there's a link right here that you can go to at Wikipedia and they show the actual components in an op amp, though it goes well beyond where we plan to go for this particular course
#electronics #youtube #knowledge #engineering #electricalengineering
Be the first to comment