1. IT2001PAEngineering Essentials (1/2)Chapter 9 - CapacitorsLecturer Namelecturer_email@ite.edu.sg Aug 16, 2012Contact Number
2. Chapter 9 - CapacitorsLesson ObjectivesUpon completion of this topic, you should be able to: Describe the constructional features of common capacitors. 2 IT2001PA Engineering Essentials (1/2)
3. Chapter 9 - CapacitorsSpecific Objectives Students should be able to : List common types of capacitors and its construction. State the application of the common types of capacitors. Explain the term di-electric. List factors affecting the capacitance of capacitor. Describe the constructional features of common capacitors. IT2001PA Engineering Essentials (1/2)
4. Chapter 9 - CapacitorsCapacitors A capacitor is a device which stores energy in the form of electric charge. In its simplest form, a capacitor consists of two metal plates separated by a thin layer of insulating material called the dielectric. 4 IT2001PA Engineering Essentials (1/2)
5. Chapter 9 - Capacitors Capacitors The basic structure of a capacitor is shown below. 5 IT2001PA Engineering Essentials (1/2)
6. Chapter 9 - Capacitors Basic Construction DIELECTRIC - an insulating (non- conducting) material. - ceramic, plastic film, mica or air.CONDUCTIVE PLATES- two parallel pieces CONNECTING LEADS separated by the dielectric. - attached to the plates-metal foil. for external connections. 6 IT2001PA Engineering Essentials (1/2)
7. Chapter 9 - CapacitorsCapacitance It is the property of a capacitor to store an electric charge when a potential difference is applied between the two plates. Symbol : C Unit : Farad (F) But usually the unit micro-farad (a sub-multiple of Farad) is used. 1 micro-farad(µF) = 10-6 Farad 7 IT2001PA Engineering Essentials (1/2)
8. Chapter 9 - CapacitorsCapacitor A capacitor has a capacitance of one farad when 1 V charges it with one coulomb of electricity. Charge (Q) Capacitance (C) = P.D. (V) Q C V Or Q= CV 8 IT2001PA Engineering Essentials (1/2)
9. Chapter 9 - CapacitorsCapacitance Q C = Q = Charge V Unit : coulomb(C)Capacitance is thus defined as the ratio of the charge stored ina capacitor to the applied voltage.The larger the capacitance, the larger will be the chargestored.A measure of a capacitor’s ability to store charge or energy. 9 IT2001PA Engineering Essentials (1/2)
10. Chapter 9 - CapacitorsExample 9-1 A capacitor stores 50µC when 10V are applied across its plates. What is its capacitance? Q C = V 50µC = 10V = 5µF 10 IT2001PA Engineering Essentials (1/2)
11. Chapter 9 - CapacitorsExample 9-2A 2µF capacitor has 100V across its plates. Howmuch charge does it store? Solution Q = CV = 2µF x 100V = 200 µC 11 IT2001PA Engineering Essentials (1/2)
12. Chapter 9 - CapacitorsExample 9-3 Determine the voltage across a 100pF capacitor which stores 2µC of charge? Q V = C 2µC = 100pF = 20kV 12 IT2001PA Engineering Essentials (1/2)
13. Chapter 9 - CapacitorsTypes of Capacitors Fixed Capacitors the capacitance cannot be changed. Variable Capacitors the capacitance can be changed. 13 IT2001PA Engineering Essentials (1/2)
14. Chapter 9 - CapacitorsTypes of Capacitors Fixed Capacitors Electrolytic (with polarities) Electrostatic Capacitor (no polarities) mica ceramic paper Variable Capacitors air capacitors trimmers 14 IT2001PA Engineering Essentials (1/2)
15. Chapter 9 - CapacitorsElectrolytic CapacitorThe type commonly used consists of twoaluminium foils, one with oxide film (+) and onewithout. 15 IT2001PA Engineering Essentials (1/2)
16. Chapter 9 - CapacitorsElectrolytic Capacitor all electrolytic capacitors are polarized. foil : aluminum; tantalum; etc. used to eliminate ripple in a dc supply. + - + - 16 IT2001PA Engineering Essentials (1/2)
17. Chapter 9 - CapacitorsElectrolytic Capacitor Electrolytic foil (aluminium or tantalum) paper or gaugesaturated with electrolyte oxide dielectic Aluminum axial-lead construction. 17 IT2001PA Engineering Essentials (1/2)
18. Chapter 9 - CapacitorsElectrolytic Capacitor Capacitance value very high. over 200 000µF. Voltage rating very low. typical maximum 350Vdc. 18 IT2001PA Engineering Essentials (1/2)
19. Chapter 9 - CapacitorsMica CapacitorIt consist of either of alternate layers of mica and metal foilclamped tightly together or thin films of silver sputtered on thetwo sides of a mica sheet. Layers are pressed together Stacked layer arrangement. and encapsulated. 19 IT2001PA Engineering Essentials (1/2)
20. Chapter 9 - CapacitorsMica Capacitor Capacitance value very small. from 1pF to 0.1µF. Voltage rating high. from 100 to 2500 Vdc. 20 IT2001PA Engineering Essentials (1/2)
21. Chapter 9 - CapacitorsCeramic Capacitor films of metal are deposited on each side of a thin ceramic disc and copper wire terminals are connected to the metal. the entire unit is encapsulated in a protective coating of plastic. used for frequency discriminating filters; DC blocking and circuits requiring close tolerance and stability. 21 IT2001PA Engineering Essentials (1/2)
22. Chapter 9 - CapacitorsCeramic CapacitorThere are two types: ceramic disc capacitors and ceramic tubular capacitors.A film of silver is deposited on both sides of the ceramic,acting as the plates. 22 IT2001PA Engineering Essentials (1/2)
23. Chapter 9 - CapacitorsCeramic Capacitor metal film ceramic disc Ceramic disk form. 23 IT2001PA Engineering Essentials (1/2)
24. Chapter 9 - CapacitorsCeramic Capacitor Capacitance value Small. from 1pF to 2.2µF. Voltage rating very high. Up to 6000Vdc. 24 IT2001PA Engineering Essentials (1/2)
25. Chapter 9 - CapacitorsPaper CapacitorThe paper capacitor consists of aluminium foil and paperdielectric rolled together and impregnated with wax or oil,and then placed in a plastic or aluminium container. 25 IT2001PA Engineering Essentials (1/2)
26. Chapter 9 - CapacitorsVariable Air Capacitor Constructed of several plates that mesh together. One set of plates can be moved relative to the other, thus changing the effective plate area and the capacitance. Used in applications requiring frequency selection radio and television receivers. RF amplifier. 26 IT2001PA Engineering Essentials (1/2)
27. Chapter 9 - CapacitorsVariable Air Capacitor movable plates (rotor) fixed plates (stator) The movable plates are all linked together mechanically so that they all move when a shaft is rotated. 27 IT2001PA Engineering Essentials (1/2)
28. Chapter 9 - CapacitorsCapacitor ApplicationsCapacitors are very widely used in electrical andelectronic applications. They can be used: in filter circuits for tuning circuits as coupling and bypass capacitors in transistoramplifiers for power factor correction in single phase motors in automobile ignition systems and for other purposes. 28 IT2001PA Engineering Essentials (1/2)
29. Chapter 9 - CapacitorsFactors Affecting Capacitance Factors that determine the capacitance of a capacitor are : plate cross-sectional area (a ). Distance distance between plates (d). dielectric permittivity (∈). a∈ C = d 29 IT2001PA Engineering Essentials (1/2)
30. Chapter 9 - CapacitorsPlate Area Capacitance (C) is directly proportional to plate cross-sectional area (a). a↑ - C↑ a↓ - C↓ full plate area reduced plate area more capacitance less capacitance 30 IT2001PA Engineering Essentials (1/2)
31. Chapter 9 - CapacitorsPlates Separation Capacitance (C) is inversely proportional to the distance between plates (d). d↑ - C↓ d↓ - C↑ narrow plate distance increased dielectric thickness more capacitance less capacitance 31 IT2001PA Engineering Essentials (1/2)
32. Chapter 9 - CapacitorsDielectric Permittivity It is a measure of the ability of a dielectric material to establish an electric field. Capacitance (C) is directly proportional to the dielectric permittivity (∈). ∈↑ - C↑ ∈↓ - C↓ 32 IT2001PA Engineering Essentials (1/2)
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