Test #3 Study Guide
Test #3 Study Guide ECE 3413
Popular in Intro to Electronic Circuits
Popular in Electrical Engineering
This 7 page Study Guide was uploaded by Caleb Jordan on Saturday February 27, 2016. The Study Guide belongs to ECE 3413 at Mississippi State University taught by Mrs. Moorhead in Winter 2016. Since its upload, it has received 193 views. For similar materials see Intro to Electronic Circuits in Electrical Engineering at Mississippi State University.
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Date Created: 02/27/16
Intro to Circuits Test #3 Study Guide Topics Covered: Operational Amplifiers Capacitors Inductors 1. Operational Amplifiers (opamps): There are a few different types of opamps that I will cover in this study guide, but before I go into them I’m going to cover things that apply to all types of op amps. So let’s get started with the general information. Opamps in General: Here’s a basic picture of an opamp that I got out of the book. The inner workings of an opamp are really complicated and not something that we are expected to learn in this class. However, there are several properties that you should know, even if you don’t understand why it works this way. V+ V = 0V Following from the previous point, V+ = V I(in) is assumed to be 0A o There is current leaving an opamp but there is no current going in R(in) is assumed to be infinite. R(out) is assumed to be 0 Ohms. V(out) = a constant A(called gain) * V(in) o V(in) in this case is the value of the voltage going into the op amp, which can be either V+ or V since they are equal. That is all the basics you need to know. Before I go into a few specific types, another assumption that has helped me solve these circuits. If you are doing nodal analysis on the circuit you can ignore the wires leading into the op amp because they have no current flowing through them. That’s not to say that you can completely ignore the opamp, just that you don’t need to mention it in your equation. If this confuses you, I’m sorry but this is very hard to explain. Just try a few practice problems. Inverting Amplifier: An Inverting Amplifier has the voltage source connected to the negative terminal and the positive terminal is grounded. This type isn’t particularly important other than just knowing the definition. If you like to see the formulas, they are on page 346 of the Intro to Electrical Engineering book. I found that most of the time they don’t apply and even when they do, you can solve the circuit without them. Summing Amplifier: The Summing Amplifier is a specific type of Inverting Amplifier that is used to sum multiple voltage sources. Differential Amplifier: This type of Amplifier focuses on amplifying the difference between two different voltage sources. So as you can see, in this case there is a voltage source connected to each terminal of the opamp. There are a few equations in the book that I don’t find useful but if you’re curious, p353. You can solve this one the same way, nodal analysis. Just remember that the opamp has no current flowing into it. 2 Capacitors & Inductors: Capacitors and Inductors are very similar so I put them in the same section. To understand Capacitor and Inductors you should think of a spring. When you push a spring together, it stores potential energy. Then when you release the spring, it releases its potential energy as kinetic energy. Capacitors and Inductors are circuit elements that do exactly that. They store energy and release it when it is needed. The difference between them is the way in which they store energy. Note: These components only work with AC current. In a DC current they cause an open circuit. Capacitors: Capacitors are comprised of two plates with a dielectric material between them. The measurement of the devices ability to store and discharge energy is known as Capacitance and is measure by the unit Farad (F). F = Coulombs/Volt As you can see, the current through a Capacitor is equal to the Capacitance multiplied by the derivative of the voltage across the Capacitor. Combining Capacitors in a circuit works the exact opposite from combining resistors. If you have two Capacitors in parallel, then you add their Capacitance. If they are in series, you follow the rules for resistors in parallel. I just put a picture here of a circuit with a few Capacitors in it so you know what they look like. The energy stored in a Capacitor can be calculated with the following equation. Sorry I don’t have a cool trick for you. It’s just a formula. Memorize it. That’s it. So your energy is equal to half the Capacitance multiplied by the voltage squared. Inductors: An Inductor is a wire coil around a core. These use electromagnetic induction to store energy, thus the name Inductors. If you are not familiar with electromagnetic induction, it’s the idea of creating current using a magnetic field. There are lots of good pictures in the book on page 139 that will help you understand this concept if you’re having trouble. Like above, here is your currentvoltage relationship for Inductors: The voltage across the Inductor is equal to the Inductance (L) multiplied by the derivative of the current through the Inductor. So L is your Inductance which is measured in henrys (H). A henry is equal to a voltsecond divided by amps. Inductors store kinetic energy instead of potential energy but have a very similar equation to Capacitors: The kinetic energy stored is equal to half your Inductance times the current through the Inductor squared. The last thing you need to know about Inductors is combining circuit elements. The rules for combining Inductors are exactly the same as resistors. I’ll put a picture here of a circuit with Inductors in it. Just review combining resistors for how to combine Inductors. That should be it. I hope this helps you study. I know making this thing really helped me. I hope you enjoyed it. If you did check back with me in the future. I will be posting a study guide for every test this semester. Happy studying and good luck on the test!!
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