Ejercicios de circuitos

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CHAPTER

Methods of Analysis of Resistive Circuits
In This Chapter:

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4.1 4.2 4.3 4.4 4.5 4.6 4.7

Introduction Node Voltage Analysis of Circuits with Current Sources Node Voltage Analysis of Circuits with Current and Voltage Sources Node Voltage Analysis withDependent Sources Mesh Current Analysis with Independent Voltage Sources Mesh Current Analysis with Current and Voltage Sources Mesh Current Analysis with Dependent Sources

4.8 4.9

The Node Voltage Method and Mesh Current Method Compared Mesh Current Analysis Using MATLAB

4.10 How Can We Check . . . ? 4.11 Design Example—Potentiometer Angle Display 4.12 Summary Problems PSpice Problems DesignProblems

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4.1 Introduction
To analyze an electric circuit, we write and solve a set of equations. We apply Kirchhoff’s current and voltage laws to get some of the equations. The constitutive equations of the circuit elements, such as Ohm’s law, provide the remaining equations. The unknown variables are element currents and voltages. Solving the equations provides the values of the elementcurrent and voltages. This method works well for small circuits, but the set of equations can get quite large for even moderate-sized circuits. A circuit with only 6 elements has 6 element currents and 6 element voltages. We could have 12 equations in 12 unknowns. In this chapter we consider two methods for writing a smaller set of simultaneous equations: • The node voltage method • The meshcurrent method The node voltage method uses a new type of variable called the node voltage. The “node voltage equations” or, more simply, the “node equations” are a set of simultaneous equations that represent a given electric circuit. The unknown variables of the node voltage equations are the node voltages. After solving the node voltage equations, we determine the values of the element currents andvoltages from the values of the node voltages. It’s easier to write node voltage equations for some types of circuit than for others. Starting with the easiest case, we will learn how to write node voltage equations for circuits that consist of: 103

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T1: IML October 17, 2005 14:13

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Methods ofAnalysis of Resistive Circuits

• Resistors and independent current sources • Resistors and independent current and voltage sources • Resistors and independent and dependent voltage and current sources The mesh current method uses a new type of variable called the mesh current. The “mesh current equations” or, more simply, the “mesh equations” are a set of simultaneous equations that represent a givenelectric circuit. The unknown variables of the mesh current equations are the mesh currents. After solving the mesh current equations, we determine the values of the element currents and voltages from the values of the mesh currents. It’s easier to write mesh current equations for some types of circuit than for others. Starting with the easiest case, we will learn how to write mesh currentequations for circuits that consist of: • Resistors and independent voltage sources • Resistors and independent current and voltage sources • Resistors and independent and dependent voltage and current sources

4.2 Node Voltage Analysis of Circuits

with Current Sources
Consider the circuit shown in Figure 4.2-1a. This circuit contains four elements: three resistors and a current source. The nodesof a circuit are the places where the elements are connected together. The circuit shown in Figure 4.2-1a has three nodes. It is customary to draw the elements horizontally or vertically and to connect these elements by horizontal and vertical lines that represent wires. In other words, nodes are drawn as points, or are drawn using horizontal or vertical lines. Figure 4.2-1b shows the same...