Download presentation

Presentation is loading. Please wait.

Published byDarrell Prest Modified over 2 years ago

1
Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2002 The McGraw-Hill Companies Grob Schultz

2
Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2003 The McGraw-Hill Companies 17 CHAPTER Capacitance

3
Topics Covered in Chapter 17 How Charge Is Stored in the Dielectric Charging and Discharging Capacitor The Farad Unit of Capacitance Typical Capacitors Electrolytic Capacitors Capacitor Color Coding

4
Parallel Capacitances Series Capacitances Stray Capacitive and Inductive Effects Energy in Electrostatic Field of Capacitance Troubles in Capacitors Topics Covered in Chapter 17 (continued)

5
Capacitor Action A capacitor consists of two conductors separated by a dielectric (insulator). Capacitors store energy in the dielectric field. Applying a voltage to a discharged capacitor causes a current to charge the capacitor. Connecting a path across the terminals of a charged capacitor causes current to flow which discharges the capacitor.

6
Electric Field in a Charged Capacitor Negative plate (conductor) Positive plate (conductor) Dielectric (insulator) } Electric lines of force

7
Capacitor Charge and Discharge (b) Capacitor charges (c) Charge holds(d) Capacitor discharges (a) No initial charge

8
The Unit of Capacitance The farad (F) is the basic unit of capacitance. One farad stores one coulomb of charge with one volt applied. Most capacitors have values less than 1 F: 1 F (microfarad) = 1 10 -6 F 1 nF (nanofarad) = 1 10 -9 F 1 pF (picofarad) = 1 10 -12 F

9
Chip Capacitors Tantalum oxide dielectric (polarized) Ceramic dielectric (non-polarized)

10
Capacitors Charge and Store Energy Charge on a capacitor, in coulombs: Q = CV Energy stored in a capacitor in joules: = ½CV 2 Where: Q = electrical charge in coulombs C = capacitance in farads V = voltage in volts = energy in joules

11
25 V 1000 F/25 V (polarized) Stored Charge Q = CV = 1000 x 10 -6 x 25 = 0.025 coulombs

12
Stored Energy This capacitor can safely store: = ½CV 2 = ½ 1000 x 10 -6 25 2 = 0.313 J 25 volts is a maximum rating. 1000 F/25 V

13
Capacitor Value Proportional to plate area (A) in meters. Inversely proportional to the spacing (d) between the plates in meters. Proportional to the dielectric constant (K ) of the material between the plates. A d C = K x 8.85 x 10 –12 F The value of a capacitor is:

14
MaterialKK Air or vacuum1 Aluminum oxide7 Ceramic80 – 1200 Glass8 Mica3 – 8 Oil2 – 5 Paper2 – 6 Plastic2 – 3 Tantalum oxide25 Dielectric Constants Plastic Ceramic Paper

15
Three Ways to Increase Capacitance Increase the dielectric constant Increase plate area Decrease plate spacing

16
Variable Capacitors The plate spacing is changed to vary the capacitance. Air dielectric variable 1 to 10 pF (trimmer capacitor) Schematic symbol Moveable concentric plates

17
Total Capacitance of Circuits Series Circuits 1111 123 CCCC etc EQ . CCCCetc T 123 . Parallel Circuits

18
Capacitors in Series and Parallel 2 F 5 F 10 F 2 F5 F 10 F C EQ = 17 F C EQ = 1.25 F

19
Voltage Distribution in a Series Circuit 50 V Q = C EQ V = 1.25 x 10 -6 x 50 = 62.5 C The charge (Q) is constant in a series circuit. 2 F 5 F 10 FC EQ = 1.25 F C1C1 C3C3 C2C2 V C 1 = Q / C 1 = 62.5 x 10 -6 / 10 x 10 -6 = 6.25 V V C 2 = Q / C 2 = 62.5 x 10 -6 / 5 x 10 -6 = 12.5 V V C 3 = Q / C 3 = 62.5 x 10 -6 / 2 x 10 -6 = 31.25 V KVL check: 6.25 + 12.5 + 31.25 = 50

20
Capacitor Defects Open Shorted Excess series resistance Leaky Generally, electrolytic capacitors are the least reliable. +

21
Safety Capacitors can store lethal charges. Some types can stay charged for months. Connecting polarized capacitors incorrectly can cause them to explode. Applying excess voltage to some capacitors can cause them to explode or ignite. Discharging large capacitors with clip leads or screwdrivers can cause a nasty arc and flying, hot metal.

Similar presentations

OK

Chapter 11 Capacitance. 2 Objectives –After completing this chapter, the student should be able to: Explain the principles of capacitance. Identify the.

Chapter 11 Capacitance. 2 Objectives –After completing this chapter, the student should be able to: Explain the principles of capacitance. Identify the.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on peak load pricing strategy Ppt on endangered animals Ppt on nepali culture and tradition Ppt on mind reading phones Download ppt on transportation in plants and animals Ppt on power electronics in ieee format Ppt on video teleconferencing equipment Funny ppt on motivation Ppt on polytene chromosomes drosophila Ppt on meaning of learning