Chapter 9 Capacitors. Objectives Describe the basic structure and characteristics of a capacitor Discuss various types of capacitors Analyze series capacitors.

Slides:



Advertisements
Similar presentations
Chapter 11 Inductors.
Advertisements

Chapter 9 Capacitors.
Chapter 15 Capacitance and RC Circuits © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Define capacitance.
Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2002 The McGraw-Hill Companies Grob Schultz.
Capacitor. Construction A capacitor is a device that sores electrical charge. It is constructed of two parallel conductive plates separated by an insulating.
Introductory Circuit Analysis Robert L. Boylestad
Capacitors Capacitance is the ability of a component to store energy in the form of an electrostatic charge. A Capacitor is a component designed to provide.
Energy Storage Devices. Objective of Lecture Describe the construction of a capacitor and how charge is stored. Introduce several types of capacitors.
BEXS100 - Basic Electricity Unit 19 Capacitors. Unit Objectives List the three (3) factors that determine the capacitance of a capacitor Explain electrostatic.
Capacitance Al Penney VO1NO.
2. Capacitor ConstructionTheory Support Electronics - AC Circuits 1 of 13 Capacitor Construction Topics covered in this presentation: Capacitor Construction.
Energy Storage Devices. Capacitors Composed of two conductive plates separated by an insulator (or dielectric). Commonly illustrated as two parallel metal.
SVES Students – you have a date in October 2016 on the Stuart Highway be looking for you “mate” prof.alan for more info contact Bindu Lakshmi, SVECW,
Capacitance and Dielectrics
electronics fundamentals
Introductory Circuit Analysis Robert L. Boylestad
ELECTRONICS TECHNOLOGY CAPACITANCE
Inductance and Capacitance
Lesson 14 – Capacitors & Inductors. Learning Objectives Define capacitance and state its symbol and unit of measurement. Predict the capacitance of a.
ELECTRICAL SKILLS CAPACITORS. FUNCTION OF A CAPACITOR Capacitors are used in electrical circuits to store electrical charges.
Capacitors in a Basic Circuit
ENGR. VIKRAM KUMAR B.E (ELECTRONICS) M.E (ELECTRONICS SYSTEM ENGG:) MUET JAMSHORO 1 CAPACITOR.
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 13.1 Capacitance and Electric Fields  Introduction  Capacitors and Capacitance.
FCI1 CHAPTER OUTLINE 1. Definition of Capacitance 2. Calculating Capacitance 3. Combinations of Capacitors 4. Energy Stored in a Charged Capacitor.
Lec. (4) Chapter (2) AC- circuits Capacitors and transient current 1.
Capacitors and Inductors.  A capacitor is a device that stores an electrical charge  It is made of two metallic plates separated by an insulator or.
Chapter 12.
Electric Circuit Capacitors Electric Circuits Capacitors DK 12.
ELECTRICITY & MAGNETISM
Energy Storage Devices Prepared By : Shingala Nital ( ) Paghdal Radhika ( ) Bopaliya Mamta ( ) Guided By : Prof. Tank.
Foundations of Physics
Electricity and Magnetism Electrostatics Capacitance and Capacitive Circuits.
Fall 2001ENGR201 Capacitance & Inductance1 Capacitor, also called electrical condenser, device for storing an electrical charge. In its simplest form a.
Chapter 1: Introduction and DC Circuit AZRALMUKMIN BIN AZMI.
1 © Unitec New Zealand DE4401 DC C APACITANCE AND CAPACITORS.
Electric Circuits Fundamentals
Fundamentals of Electric Circuits Chapter 6
Chapter 10 Capacitors and Capacitance. 2 Capacitance Capacitor –Stores charge –Two conductive plates separated by insulator –Insulating material called.
16 Capacitance Chapter Topics Covered in Chapter 16
Chapter 12 Principles of Electric Circuits, Conventional Flow, 9 th ed. Floyd © 2010 Pearson Higher Education, Upper Saddle River, NJ All Rights.
 BY: PAWAN JAISWAL En.no: PARTH SHAH En.no: Guided By: Prof. Ullash Gohil 1 st SEM Computer Engineering UNIVERSAL COLLEGE OF.
Capacitors are one of the fundamental passive components. In its most basic form, it is composed of two conductive plates separated by an insulating dielectric.
CAPACITORS. A capacitor is a device used to “store” electric charge. It can store energy and release it very quickly!!
Chapter 25 Lecture 20: Capacitor and Capacitance.
EGR 1011 Capacitors Chapter 12. EGR 1012 Capacitance – the ability of a component to store energy by accumulating charge A capacitor is a circuit component.
1 AGBell – EECT by Andrew G. Bell (260) Chapter 17 Capacitance.
Capacitor Engr. Faheemullah Shaikh Lecturer, Department of Electrical Engineering.
Capacitors The capacitor is an element that continuously stores charge (energy), for later use over a period of time! In its simplest form, a capacitor.
Chapter 11 Capacitance. 2 Objectives –After completing this chapter, the student should be able to: Explain the principles of capacitance. Identify the.
Capacitors AC Circuits I. Capacitors and Capacitance: An Overview Capacitance – the ability of a component to store energy in the form of an electrostatic.
Chapter 10 RC Circuits.
Chapter 9 CAPACITOR.
Capacitance. Device that stores electric charge. Construction: A capacitor is two conducting plates separated by a finite distance Typically separated.
RC Circuits (sine wave)
CAPACITORS & CAPACITANCE
Lesson 11: Capacitors (Chapter 10) and Inductors (Chapter 11)
Electric Circuits Fall, 2014
Capacitors Capacitance is the ability of a component to store energy in the form of an electrostatic charge. A Capacitor is a component designed to provide.
Chapter 11 Capacitance.
Chapter 11 Inductors.
Capacitance and Dielectrics
Capacitors A capacitor is a device for storing charge and electrical potential energy. All capacitors consists of two metal plates separated by an insulator.
CAPACITANCE.
electronics fundamentals
Potential Difference and Capacitance
Principles & Applications
ECE131 BASIC ELECTRICAL & ELECTRONICS ENGG
Fundamentals of Electric Circuits Chapter 6
Chapter 9 Capacitors.
Electric Circuits Fall, 2017
Presentation transcript:

Chapter 9 Capacitors

Objectives Describe the basic structure and characteristics of a capacitor Discuss various types of capacitors Analyze series capacitors Analyze parallel capacitors Analyze capacitive dc switching circuits Analyze capacitive ac circuits

Basics of a Capacitor In its simplest form, a capacitor is an electrical device constructed of two parallel plates separated by an insulating material called the dielectric. In the neutral state, both plates have an equal number of free electrons. When a voltage source is connected to the capacitor, electrons are removed from one plated and deposited on the other. No electrons flow through the dielectric.

Basics of a Capacitor

When the supply is removed from the capacitor, the capacitor retains the stored charge. The amount of charge that a capacitor can store per volt across the plates is its capacitance (C). The unit of capacitance is the farad (F). One farad is the amount of capacitance when one coulomb of charge is stored with one volt across the plates. Most capacitors in electronics work have capacitance values of  F (10 -6 F) or  F ( F).

How a Capacitor Stores Energy A capacitor stores energy in the form of an electric field that is established by the opposite charges on the two plates. A capacitor obeys Coulomb’s Law: A force exists between two point-source charges that is directly proportional to the product of the two charges and inversely proportional to the square of the distance between the charges. F = k Q 1 Q 2 / d 2 k = 9x10 9 newton- meter 2 /coulumb 2

Capacitor Ratings The voltage rating specifies the maximum dc voltage that can be applied without risk of damage to the device (breakdown or working voltage) determined by the dielectric strength. (expressed in Volt/ mil (1 mil = 0.001in)) Temperature coefficient indicates the amount and direction of a change of capacitance with temperature. positive coefficient means that capacitance increases with increasing temp, while a negative coefficient means capacitance decreases with increasing temp. positive coefficient means that capacitance increases with increasing temp, while a negative coefficient means capacitance decreases with increasing temp.

dielectric strength of Material MaterialDielectric Strength (V/m) Air3e6 Bakelite24e6 Neoprene rubber12e6 Nylon14e6 Paper16e6 Polystyrene24e6 Pyrex glass14e6 Quartz8e6 Silicone oil15e6 Strontium titanate8e6 Teflon60e6

Characteristics of a Capacitor Capacitance is directly proportional to the physical size of the plates as determined by the plate area. Capacitance is inversely proportional to the distance between the plates. The measure of a materials’ ability to establish an electric field is called the dielectric constant (  ). Capacitance is directly proportional to the dielectric constant.  r (8.85 x F/m) /d C = A  r (8.85 x F/m) /d

Fixed Capacitors Stacked-foil mica capacitors are made of alternate layers of metal foil and thin sheets of mica. Silver mica are formed by stacking mica sheets with silver electrode material screened on them.

Fixed Capacitors Ceramic dielectrics provide very high dielectric constants, and relatively large capacitance in a small physical size. Capacitance ranges from 1pF to 2.2  F.

Electrolytic Capacitors Electrolytic capacitors are polarized so that one plate is positive, and the other negative. They come in capacitance values from 1  F to 200,000  F, with voltage ratings to 350 V.

Electrolytic Capacitors Two common types of electrolytic capacitors are Aluminum and Tantalum electrolytic. The voltage polarity of these devices must be observed, as reversal of polarity will usually result in complete destruction of the capacitor.

A supercapacitor A supercapacitor or ultracapacitor is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors. They are of particular interest in automotive applications for hybrid vehicles and as supplementary storage for battery electric vehicles. capacitorenergy densityhybrid vehiclesbattery electric vehiclescapacitorenergy densityhybrid vehiclesbattery electric vehicles

Variable Capacitors Variable capacitors are used in circuits when there is a need to adjust the capacitance value. Ceramic or mica is a common dielectric. Capacitance is changed by plate separation.

Capacitor Labeling Capacitors use several standard labeling methods; we will consider a small ceramic capacitor: values marked as.001 or.01 have units of microfarads. values marked as.001 or.01 have units of microfarads. values marked as 50 or 330 have units of picofarads. values marked as 50 or 330 have units of picofarads. a value of 103 or 104 would be 10x10 3 (10,000 pF) or 10x10 4 (100,000 pF) respectively. a value of 103 or 104 would be 10x10 3 (10,000 pF) or 10x10 4 (100,000 pF) respectively. The units may be on the capacitor as pF or  F (  F may be written a MF or MFD). The units may be on the capacitor as pF or  F (  F may be written a MF or MFD).

Series Capacitors When capacitors are connected in series, the total capacitance is less than the smallest capacitance value since the effective plate separation increases. 1/C T = 1/C 1 + 1/C 2 + 1/C 3 + … + 1/C n

Parallel Capacitors The total parallel capacitance is the sum of all capacitors in parallel. C T = C 1 + C 2 + C 3 + … + C n

Capacitors in DC Circuits A capacitor will charge up when it is connected to a dc voltage source. When a capacitor is fully charged, there is no current. There is no current through the dielectric of the capacitor because the dielectric is an insulating material. A capacitor blocks constant dc.

RC Time Constant The buildup of charge across the plates occurs in a predictable manner that is dependent on the capacitance and the resistance in a circuit. The time constant of a series RC circuit is a time interval that equals the product of the resistance and the capacitance.  = RC

Charging and Discharging The charging curve is an increasing exponential. The discharging curve is an decreasing exponential.

Transient time It takes 5 time constants to change the voltage by 99% (charging or discharging), this is called the transient time.

Capacitors in ac Circuits The instantaneous capacitor current is equal to the capacitance times the instantaneous rate of change of the voltage across the capacitor. This rate of change is a maximum positive when the rising sine wave crosses zero. This rate of change is a maximum negative when the falling sine wave crosses zero. The rate of change is zero at the maximum and minimum of the sine wave.

Capacitive Reactance, X C Capacitive reactance (X C ) is the opposition to sinusoidal current, expressed in ohms. The rate of change of voltage is directly related to frequency. As the frequency increases, the rate of change of voltage increases, and thus current ( i ) increases. An increase in i means that there is less opposition to current (X C is less). X C is inversely proportional to i and to frequency.

Capacitive Reactance, X C The relationship between capacitive reactance, capacitance and frequency is: X C = 1/(2  f C) where:X C is in ohms (  ) f is in hertz (Hz) C is in farads (F)

Analysis of Capacitive ac Circuit The current leads the voltage by 90  in a purely capacitive ac circuit. The resulting current can be expressed in polar form as I  90  or in rectangular form as jI.

Power in a Capacitor Energy is stored by the capacitor during a portion of the voltage cycle; then the stored energy is returned to the source during another portion of the cycle. Instantaneous power is the product of v and i. True power (P true ) is zero, since no energy is consumed by the capacitor. The rate at which a capacitor stores or returns energy is called reactive power (P r ); units: (VAR). P r =V rms I rms ; P r = V 2 rms / X c ; P r = I 2 rms X c

Capacitor Applications Capacitors are used for filtering in power supplies. Since capacitors do not pass dc, they are used for dc blocking and ac coupling. For power line decoupling, capacitors are connected between the dc supply and ground, to suppress unwanted voltage spikes that occur on the dc supply voltage due to fast switching. Capacitors are used to bypass an ac voltage around a resistor without affecting the dc resistance.

Capacitor Applications Capacitors are used in filters, to select one ac signal with a certain specified frequency from a wide range of signals with many different frequencies. For example, the selection of one radio station and rejecting the others. Capacitors are used in timing circuits to generate time delays, based on the RC time constant. Dynamic memories used in computers are simply very tiny capacitors used as a storage element.

Summary A capacitor is composed of two parallel conducting plates separated by a dielectric insulator. Energy is stored by a capacitor in the electric field between the plates. One farad is the amount of capacitance when one coulomb of charge is stored with one volt across the plates.

Summary Capacitance is directly proportional to the plate area and inversely proportional to the plate separation. Dielectric constant is an indication of the ability of a material to establish an electric field. Dielectric strength is one factor that determines the breakdown voltage of a capacitor. A capacitor blocks constant dc.

Summary The time constant for a series RC circuit is the resistance times the capacitance. In an RC circuit, the voltage and current in a charging or discharging capacitor make a 63% change during each time-constant interval. 5 time constants are required of a capacitor to fully charge or to discharge fully. This is called the transient time. Charging and discharging are exponential curves.

Summary Total series capacitance is less than that of the smallest capacitor in series. Capacitance adds in parallel. Current leads voltage by 90  in a capacitor. X C is inversely proportional to frequency and capacitance. The true power in a capacitor is zero; that is, there is no energy loss in an ideal capacitor.