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2. Capacitors Contents 2. Capacitors Contents 1 Capacitor 1 1.1 History ................................................. 2 1.2 Theory of operation .......................................... 2 1.2.1 Overview ........................................... 3 1.2.2 Hydraulic analogy ....................................... 3 1.2.3 Energy of electric field .................................... 4 1.2.4 Current–voltage relation ................................... 4 1.2.5 DC circuits .......................................... 4 1.2.6 AC circuits .......................................... 5 1.2.7 Laplace circuit analysis (s-domain) .............................. 5 1.2.8 Parallel-plate model ...................................... 5 1.2.9 Networks ........................................... 6 1.3 Non-ideal behavior .......................................... 7 1.3.1 Breakdown voltage ...................................... 7 1.3.2 Equivalent circuit ....................................... 7 1.3.3 Q factor ............................................ 8 1.3.4 Ripple current ......................................... 8 1.3.5 Capacitance instability .................................... 8 1.3.6 Current and voltage reversal ................................. 9 1.3.7 Dielectric absorption ..................................... 9 1.3.8 Leakage ............................................ 9 1.3.9 Electrolytic failure from disuse ................................ 9 1.4 Capacitor types ............................................ 9 1.4.1 Dielectric materials ...................................... 10 1.4.2 Structure ........................................... 11 1.5 Capacitor markings .......................................... 11 1.5.1 Example ............................................ 12 1.6 Applications .............................................. 12 1.6.1 Energy storage ........................................ 12 1.6.2 Pulsed power and weapons .................................. 12 1.6.3 Power conditioning ...................................... 12 1.6.4 Suppression and coupling ................................... 13 i ii CONTENTS 1.6.5 Motor starters ......................................... 14 1.6.6 Signal processing ....................................... 14 1.6.7 Sensing ............................................ 14 1.6.8 Oscillators ........................................... 15 1.7 Hazards and safety ........................................... 15 1.8 See also ................................................ 15 1.9 References ............................................... 16 1.10 Bibliography .............................................. 16 1.11 External links ............................................. 17 2 Types of capacitor 18 2.1 General remarks ........................................... 18 2.1.1 Theory of conventional construction ............................. 18 2.1.2 Theory of electrochemical construction ........................... 19 2.1.3 Common capacitors and their names ............................. 19 2.1.4 Dielectrics .......................................... 20 2.1.5 Capacitance and voltage range ................................ 21 2.1.6 Miniaturization ........................................ 21 2.1.7 Overlapping range of applications .............................. 21 2.2 Types and styles ............................................ 21 2.2.1 Ceramic capacitors ...................................... 22 2.2.2 Film capacitors ........................................ 22 2.2.3 Film power capacitors .................................... 23 2.2.4 Electrolytic capacitors .................................... 24 2.2.5 Supercapacitors ........................................ 25 2.2.6 Class X and Class Y capacitors ................................ 26 2.2.7 Miscellaneous capacitors ................................... 26 2.2.8 Variable capacitors ...................................... 27 2.3 Comparison of types ......................................... 27 2.4 Electrical characteristics ....................................... 27 2.4.1 Series-equivalent circuit ................................... 27 2.4.2 Standard capacitance values and tolerances ......................... 28 2.4.3 Temperature dependence ................................... 28 2.4.4 Frequency dependence .................................... 28 2.4.5 Voltage dependence ..................................... 28 2.4.6 Rated and category voltage .................................. 29 2.4.7 Impedance .......................................... 29 2.4.8 Inductance (ESL) and self-resonant frequency ........................ 30 2.4.9 Ohmic losses, ESR, dissipation factor, and quality factor .................. 31 2.4.10 Limiting current loads .................................... 31 2.4.11 Insulation resistance and self-discharge constant ....................... 33 2.4.12 Leakage current ....................................... 34 CONTENTS iii 2.4.13 Microphonics ......................................... 34 2.4.14 Dielectric absorption (soakage) ................................ 35 2.4.15 Energy density ........................................ 35 2.4.16 Long time behavior, aging .................................. 35 2.4.17 Failure rate .......................................... 36 2.5 Additional information ........................................ 37 2.5.1 Soldering ........................................... 37 2.5.2 Electrolytic behavior from storage or disuse ......................... 37 2.5.3 IEC/EN standards ...................................... 37 2.5.4 Capacitor symbols ...................................... 38 2.5.5 Markings ........................................... 38 2.5.6 Polarity marking ....................................... 39 2.6 Market segments ........................................... 39 2.7 See also ................................................ 39 2.8 References .............................................. 39 2.9 External links ............................................. 41 3 Farad 42 3.1 Definition ............................................... 42 3.1.1 Equalities ........................................... 42 3.2 History ................................................ 42 3.3 Explanation .............................................. 42 3.3.1 Informal terminology ..................................... 43 3.3.2 Related concepts ....................................... 43 3.4 CGS units ............................................... 43 3.5 See also ................................................ 43 3.6 Notes ................................................. 43 3.7 External links ............................................. 43 3.8 Text and image sources, contributors, and licenses .......................... 44 3.8.1 Text .............................................. 44 3.8.2 Images ............................................ 45 3.8.3 Content license ........................................ 47 Chapter 1 Capacitor This article is about the electronic component. For the physical phenomenon, see capacitance. For an overview of various kinds of capacitors, see types of capacitor. “Capacitive” redirects here. For the term used when re- ferring to touchscreens, see capacitive sensing. A capacitor (originally known as a condenser) is a 4 electrolytic capacitors of different voltages and capacitance Miniature low-voltage capacitors (next to a cm ruler) Solid electrolyte, resin-dipped 10 μF 35 V tantalum capacitors. The + sign indicates the positive lead. or sintered beads of metal or conductive electrolyte, etc. The nonconducting dielectric acts to increase the capaci- tor’s charge capacity. A dielectric can be glass, ceramic, plastic film, air, vacuum, paper, mica, oxide layer etc. Capacitors are widely used as parts of electrical circuits A typical electrolytic capacitor in many common electrical devices. Unlike a resistor, an passive two-terminal electrical component used to store ideal capacitor does not dissipate energy. Instead, a ca- energy electrostatically in an electric field. The forms of pacitor stores energy in the form of an electrostatic field practical capacitors vary widely, but all contain at least between its plates. two electrical conductors (plates) separated by a dielectric When there is a potential difference across the conductors (i.e. insulator). The conductors can be thin films, foils (e.g., when a capacitor is attached across a battery), an 1 2 CHAPTER 1. CAPACITOR electric field develops across the dielectric, causing posi- tive charge +Q to collect on one plate and negative charge −Q to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if a time-varying voltage is applied across the leads of the capacitor, a displacement current can flow. An ideal capacitor is characterized by a single constant value for its capacitance. Capacitance is expressed as the ratio of the electric charge Q on each conductor to the potential difference V between them. The SI unit of ca- pacitance is the farad (F), which is equal to one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10−12 F) to about 1 mF (10−3 F). The capacitance is greater when there is a narrower sepa- ration between conductors and when the conductors have a larger surface area. In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an undesired
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