Chapter 7 First-Order Circuit SJTU.

Slides:



Advertisements
Similar presentations
Lecture 2 Operational Amplifiers
Advertisements

SJTU1 Chapter 3 Methods of Analysis. SJTU2 So far, we have analyzed relatively simple circuits by applying Kirchhoffs laws in combination with Ohms law.
Chapter 9 Sinusoids and Phasors SJTU.
Previous Lectures Source free RL and RC Circuits.
Reading Assignment: Chapter 8 in Electric Circuits, 9th Ed. by Nilsson
Chapter 8 Second-Order Circuit SJTU.
Differential Equations
NATURAL AND STEP RESPONSES OF RLC CIRCUITS
Review 0、introduction 1、what is feedback?
Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Chapter 2 Basic laws SJTU.
Ch3 Basic RL and RC Circuits
Chapter 11 AC power analysis SJTU.
Direct-Current Circuits
Lecture 10: RL & RC Circuits Nilsson & Riedel ENG17 (Sec. 2): Circuits I Spring May 1, 2014.
Chapter 4 Circuit Theorems SJTU.
Fisica Generale - Alan Giambattista, Betty McCarty Richardson Copyright © 2008 – The McGraw-Hill Companies s.r.l. 1 Chapter 21: Alternating Currents Sinusoidal.
Magnetically coupled circuits
Leo Lam © Signals and Systems EE235. Leo Lam © Breeding What do you get when you cross an elephant and a zebra? Elephant zebra sin.
Multivibrators and the 555 Timer
Chapter 30.
Sinusoidal steady-state analysis
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 18.1 Transient Behaviour  Introduction  Charging Capacitors and Energising.
Department of Electronic Engineering BASIC ELECTRONIC ENGINEERING Transients Analysis.
First Order Circuit Capacitors and inductors RC and RL circuits.
Department of Electronic Engineering BASIC ELECTRONIC ENGINEERING Transients Analysis.
Series RLC Network. Objective of Lecture Derive the equations that relate the voltages across a resistor, an inductor, and a capacitor in series as: the.
Chapter 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
First Order Circuits. Objective of Lecture Explain the operation of a RC circuit in dc circuits As the capacitor releases energy when there is: a transition.
Source-Free RLC Circuit
Lecture - 8 First order circuits. Outline First order circuits. The Natural Response of an RL Circuit. The Natural Response of an RC Circuit. The Step.
Parallel RLC Network. Objective of Lecture Derive the equations that relate the voltages across a resistor, an inductor, and a capacitor in parallel as:
Chapter 7. First and second order transient circuits
Series RLC Network. Objective of Lecture Derive the equations that relate the voltages across a resistor, an inductor, and a capacitor in series as: the.
Sinusoidal Steady-state Analysis Complex number reviews Phasors and ordinary differential equations Complete response and sinusoidal steady-state response.
Chapter 7 In chapter 6, we noted that an important attribute of inductors and capacitors is their ability to store energy In this chapter, we are going.
09/16/2010© 2010 NTUST Today Course overview and information.
Fundamentals of Electric Circuits Chapter 7
ES250: Electrical Science
1 Circuit Theory Chapter 7 First-Order Circuits see "Derivation" link for more information.
ECE 2300 Circuit Analysis Dr. Dave Shattuck Associate Professor, ECE Dept. Lecture Set #13 Step Response W326-D3.
The V  I Relationship for a Resistor Let the current through the resistor be a sinusoidal given as Is also sinusoidal with amplitude amplitudeAnd.
Step Response Series RLC Network.
Chapter 7 In chapter 6, we noted that an important attribute of inductors and capacitors is their ability to store energy In this chapter, we are going.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc. Lecture 13 RC/RL Circuits, Time.
First Order And Second Order Response Of RL And RC Circuit
Lecture 18 Review: Forced response of first order circuits
Chapter 5 First-Order and Second Circuits 1. First-Order and Second Circuits Chapter 5 5.1Natural response of RL and RC Circuit 5.2Force response of RL.
Source-Free Series RLC Circuits.
A sinusoidal current source (independent or dependent) produces a current That varies sinusoidally with time.
Lecture - 7 First order circuits. Outline First order circuits. The Natural Response of an RL Circuit. The Natural Response of an RC Circuit. The Step.
CHAPTER 5 DC TRANSIENT ANALYSIS.
Lecture -5 Topic :- Step Response in RL and RC Circuits Reference : Chapter 7, Electric circuits, Nilsson and Riedel, 2010, 9 th Edition, Prentice Hall.
Ch3 Basic RL and RC Circuits 3.1 First-Order RC Circuits 3.2 First-Order RL Circuits 3.3 Exemples Readings Readings: Gao-Ch5; Hayt-Ch5, 6 Circuits and.
INC 111 Basic Circuit Analysis Week 9 RC Circuits.
1 College of Communication Engineering Undergraduate Course: Signals and Linear Systems Lecturer: Kunbao CAI.
1.5. General Second Order Circuits
Inductance and Capacitance Response of First Order RL and RC
Ing shap e Wav 1.
First Order And Second Order Response Of RL And RC Circuit
EKT101 Electric Circuit Theory
Source-Free RLC Circuit
Chapter 7 – Response of First Order RL and RC Circuits
Alexander-Sadiku Fundamentals of Electric Circuits
2. 2 The V-I Relationship for a Resistor Let the current through the resistor be a sinusoidal given as Is also sinusoidal with amplitude amplitude.
Chapter 7 In chapter 6, we noted that an important attribute of inductors and capacitors is their ability to store energy In this chapter, we are going.
Electric Circuits Fall, 2017
Mechatronics Engineering
First Order Circuit Capacitors and inductors RC and RL circuits.
Apply KCL to the top node ,we have We normalize the highest derivative by dividing by C , we get Since the highest derivative in the equation is.
Presentation transcript:

Chapter 7 First-Order Circuit SJTU

First-order Circuit Complete Response Initial and Final Conditions Items: RC and RL Circuits First-order Circuit Complete Response Initial and Final Conditions First-order Circuit Sinusoidal Response SJTU

1. RC and RL Circuits Two major steps in the analysis of a dynamic circuit use device and connection equations to formulate a differential equation. solve the differential equation to find the circuit response. SJTU

FORMULATING RC AND RL CIRCUIT EQUATIONS   SJTU

Eq.(7-1) RC Eq.(7-2) Eq.(7-3) Eq.(7-4) . Eq.(7-5) RL Eq.(7-6) SJTU

ZERO-INPUT RESPONSE OF FIRST-ORDER CIRCUITS RC Circuit: makes VT=0 in Eq.(7-3) we find the zero-input response Eq.(7-7) Eq.(7-7) is a homogeneous equation because the right side is zero. A solution in the form of an exponential Eq.(7-8) where K and s are constants to be determined SJTU

characteristic equation Substituting the trial solution into Eq.(7-7) yields                                        OR                                      Eq.(7-9) characteristic equation a single root of the characteristic equation zero -input response of the RC circuit: SJTU

Fig. 7-3: First-order RC circuit zero-input response Eq.(7-10) time constant TC=RTC Fig. 7-3: First-order RC circuit zero-input response SJTU

Graphical determination of the time constant T from the response curve SJTU

RL Circuit: Eq.(7-11) Eq.(7-12) The root of this equation The final form of the zero-input response of the RL circuit is Eq.(7-13)   SJTU

EXAMPLE 7-1 The switch in Figure 7- 4 is closed at t=0, connecting a capacitor with an initial voltage of 30V to the resistances shown. Find the responses vC(t), i(t), i1(t) and i2(t) for t  0.   Fig. 7-4 SJTU

SOLUTION: SJTU

EXAMPLE 7-2 Find the response of the state variable of the RL circuit in Figure 7-5 using L1=10mH, L2=30mH, R1=2k ohm, R2=6k ohm, and iL(0)=100mA Fig. 7-5 SJTU

SOLUTION: SJTU

2. First-order Circuit Complete Response When the input to the RC circuit is a step function** Eq.(7-15) The response is a function v(t) that satisfies this differential equation for t 0 and meets the initial condition v(0). If v(0)=0, it is Zero-State Response. Since u(t)=1 for t  0 we can write Eq.(7-15) as Eq.(7-16)   SJTU

divide solution v(t) into two components: natural response forced response The natural response is the general solution of Eq.(7-16) when the input is set to zero. SJTU

seek a particular solution of the equation The forced response is a particular solution of Eq.(7-16) when the input is step function. seek a particular solution of the equation Eq.(7-19) The equation requires that a linear combination of VF(t) and its derivative equal a constant VA for t  0. Setting VF(t)=VA meets this condition since . Substituting VF=VA into Eq.(7-19) reduces it to the identity VA=VA. Now combining the forced and natural responses, we obtain SJTU

Fig. 7-12: Step response of first-order RC circuit using the initial condition:  K=(VO-VA) The complete response of the RC circuit: Eq.(7-20) The zero-state response of the RC circuit: t0 Fig. 7-12: Step response of first-order RC circuit SJTU

the initial and final values of the response are The RL circuit in Figure 7-2 is the dual of the RC circuit Eq.(7-21) Setting iF=IA SJTU

The constant K is now evaluated from the initial condition:                                                          The initial condition requires that K=IO-IA, so the complete response of the RL circuit is Eq.(7-22)   The zero-state response of the RC circuit: t0 SJTU

The complete response of a first-order circuits depends on three quantities: The amplitude of the step input (VA or IA) The circuit time constant(RTC or GNL)  The value of the state variable at t=0 (VO or IO) SJTU

Find the response of the RC circuit in Figure 7-13 EXAMPLE 7-4 Find the response of the RC circuit in Figure 7-13 SOLUTION: SJTU

SJTU

EXAMPLE 7-5 Find the complete response of the RL circuit in Figure 7-14(a). The initial condition is i(0)=IO Fig. 7-14 SJTU

SJTU

(a) What is the circuit time constant? EXAMPLE 7-6 The state variable response of a first-order RC circuit for a step function input is                                                           (a) What is the circuit time constant? (b) What is the initial voltage across the capacitor? (c) What is the amplitude of the forced response? (d) At what time is VC(t)=0? SJTU

(b) The initial (t=0) voltage across the capacitor is SOLUTION: (a) The natural response of a first-order circuit is of the form        . Therefore, the time constant of the given responses is Tc=1/200=5ms (b) The initial (t=0) voltage across the capacitor is                                                                  (c) The natural response decays to zero, so the forced response is the final value vC(t).                                                                     (d) The capacitor voltage must pass through zero at some intermediate time, since the initial value is positive and the final value negative. This time is found by setting the step response equal to zero:                                  which yields the condition                          SJTU

COMPLETE RESPONSE The first parts of the above equations are Zero-input response and the second parts are Zero-state response. What is s step response? SJTU

EXAMPLE 7-7 Find the zero-state response of the RC circuit of Figure 7-15(a) for an input                                                 Fig. 7-15 SJTU

The first input causes a zero-state response of                                                The second input causes a zero-state response of                                                            The total response is the superposition of these two responses.                                        Figure 7-15(b) shows how the two responses combine to produce the overall pulse response of the circuit. The first step function causes a response v1(t) that begins at zero and would eventually reach an amplitude of +VA for t>5RC. However, at t=T<5TC the second step function initiates an equal and opposite response v2(t). For t> T+5RC the second response reaches its final state and cancels the first response, so that total pulse response returns to zero. SJTU

3. Initial and Final Conditions Eq.(7-23) the general form :                                                                                                                SJTU

The state variable response in switched dynamic circuits is found using the following steps: STEP 1: Find the initial value by applying dc analysis to the circuit configuration for t<0 STEP 2: Find the final value by applying dc analysis to the circuit configuration for t>0. STEP 3: Find the time constant TC of the circuit in the configuration for t>0 STEP 4: Write the step response directly using Eq.(7-23) without formulating and solving the circuit differential equation. SJTU

Example: The switch in Figure 7-18(a) has been closed for a long time and is opened at t=0. We want to find the capacitor voltage v(t) for t0 Fig. 7-18: Solving a switched dynamic circuit using the initial and final conditions SJTU

SJTU

There is another way to find the nonstate variables. Generally, method of “three quantities” can be applied in step response on any branch of First-order circuit. Get f(0) from initial value of state variable Get f()---use equivalent circuit Get TC---calculate the equivalent resistance Re, TC=ReC or L/ Re Then, SJTU

How to get initial value f(0)? the capacitor voltage and inductor current are always continuous in some condition. Vc(0+)=Vc(0-); IL(0+)=IL(0-) ---use 0+ equivalent circuit C: substituted by voltage source; L: substituted by current source Find f(0) in the above DC circuit. How to get final value f(∞)? Use ∞ equivalent circuit(stead state) to get f(∞). C: open circuit; L: short circuit How to get time constant TC? The key point is to get the equivalent resistance Re. SJTU

forced response natural response Zero-input response Zero-state response SJTU

EXAMPLE 7-8 The switch in Figure 7-20(a) has been open for a long time and is closed at t=0. Find the inductor current for t>0. SOLUTION: Fig. 7-20 SJTU

EXAMPLE 7-9 The switch in Figure 7-21(a) has been closed for a long time and is opened at t=0. Find the voltage vo(t) Fig. 7-21 SJTU

another way to solve the problem: SJTU

4. First-Order Circuit Sinusoidal Response If the input to the RC circuit is a casual sinusoid Eq.(7-24) SJTU

where SJTU

EXAMPLE 7-12 The switch in Figure 7-26 has been open for a long time and is closed at t=0. Find the voltage v(t) for t  0 when vs(t)=[20 sin 1000t]u(t)V. SOLUTION: Fig. 7-26 SJTU

Summary Circuits containing linear resistors and the equivalent of one capacitor or one inductor are described by first-order differential equations in which the unknown is the circuit state variable. The zero-input response in a first-order circuit is an exponential whose time constant depends on circuit parameters. The amplitude of the exponential is equal to the initial value of the state variable. The natural response is the general solution of the homogeneous differential equation obtained by setting the input to zero. The forced response is a particular solution of the differential equation for the given input. For linear circuits the total response is the sum of the forced and natural responses. SJTU

Summary For linear circuits the total response is the sum of the zero-input and zero-state responses. The zero-input response is caused by the initial energy stored in capacitors or inductors. The zero-state response results form the input driving forces. The initial and final values of the step response of a first and second-order circuit can be found by replacing capacitors by open circuits and inductors by short circuits and then using resistance circuit analysis methods. For a sinusoidal input the forced response is called the sinusoidal steady-state response, or the ac response. The ac response is a sinusoid with the same frequency as the input but with a different amplitude and phase angle. The ac response can be found from the circuit differential equation using the method of undetermined coefficients Homework: zero-input: 7.6 7.8 7.14 7.21 step response:7.35 7.36 7.55 op amp : 7.597.62 SJTU