00730293 Capacitors-Various Dielectrics and Their Applications

8/13/2019 00730293 Capacitors-Various Dielectrics and Their Applications

1/7

Capacitors - Various Dielectrics and Their ApplicationsCletus J. Kaiser

Writer / Consultant2851 W. 127th Street

Olathe KS 66061Phone: 913-764-3577 Fax: 913-764-8909

ABSTRACT Proper component selection is th ej ir ststep in building reliuble equipment. To select the correctcapacitor to be used the designer must know us much aspossible ubout the different types. The designer shouldknow the udvuntuges und disudvuntuges; the behuviorunder vurious environmentul conditions; the coiistruction;the effect of circuits on cupucitors; nd ivhut niukescupucitors fuiL TIiis puper will uddr ss the diyjereiit typesof cupucitors und give some guidunce in their upplicutions.

INTRODUCTION

Capacitors are used as energy storage components toaccumulate energy and then to discharge the energy overtime. The presence of electrical charges o n the electrodes ofa capacitor induces charges in the dielectric. These inducedcharges determine something called permittivity. Eachdielectric material has its own value of permittivity.Permittivity introduces a more practical and better knownvalue called K or dielectric constant. K is defined as theratio of the perm ittivity of the dielectric to the perm ittivity offree space a vacuum. Therefore, all the capacitance valuesare related to the perm ittivity of a vacuum. In a vacuum, K1, while K for every material has some value greater than 1.The higher the K, the more capacitance with all othervariables being equal. The use of higher values of K reducesthe size. However, capacitors with low values of K areavailable for other capacitor cliaracteristics such as stabilityand voltage ratings.

The following chart illustrates the Dielectric Constants ofmaterials used in capacitors today.

INSULATORAir or VacuumPaperPlasticMineral OilSilicon OilQGlassPorcelainMicaAluminum OxideTantalum OxideBarium TitanateCeramic

K - VALUE1.02.0 6.02.1 6.02.2 - 2.32.7 2.83.8 4.44.8 8.05.1 5.95.4 8.78.4261 000 3,00012 400 000

A timing circuit is a good example of a DC application.The RC timing circuit uses a combination of resistance andcapacitance to determine its operation. When energized, allthe voltage would first appear across the resistor and noneacross the capacitor. The voltage across the resistor woulddecrease with time just as the voltage across the capacitorincreases with time. The capacitor blocks the flow of DConce it is charged.The storage capability of the capacitor is used for the

application of capacitors in filters. Basic DC power suppliesprovide an output (the voltage across a load) which isfluctuating. To smooth these fluctuations, add a capacitorparallel to the load.When a capacitor is subjected to alterna ting current, to thecapacitor it looks like DC which is flowing in and flowingout again. The capacitor is alternately being charged,discharged, and then recharged in the opposite directionbefore being discharged again. The capacitor, in an ACcircuit, is acting something like a resistor in a DC circuitwith the additional dimension of frequency to take intoconsideration. The two effects of frequency and capacitanceare combined in an expression known as capacitive

reactance.There is a comparable expression for inductance whichyields inductive reactance. Inductance arises from the leadwires which are attached to the capacitor or electrodes. Asclock rates increase, manufacturers are now designingcapacitors to minimize inductance.

0-7803-4943-1/98/ 10.00 1998IEEE 1155


2/7

An ideal capacitor would produce no heat when currentpasses through it. The heat which is produced comes fromthe resistance which manufacturers are unable to eliminatecompletely. Because of this, a measure of the resistance isfrequently specified as an expression called DF(dissipation factor). Th e expression for DF is defined as theratio of resistance to capacitive reactance. The higher theresistance, the higher the DF and generally the worse thecapacitor. In good capacitors the DF is rather small. DF isfrequently expressed in percent (%).

Manufacturers establish how much power each physicalsize of capacitor can handle without getting too hot. If thecapacitor gets too hot, the failure rate goes up. The peakvoltage rating should not be exceeded by anything not byDC nor by the peak AC so the peak value must becalculated as a second restriction in AC applications.Film capacitors and ceramic capacitors are not polardevices. They will work equally well with either positive ornegative polarity. Electrolytic capacitors, however, are not soflexible, and ca nnot allow much reverse voltage. If pure ACwere applied, the voltage would be in reverse half the time.The answer to this dilemma is called bias voltage. Both ACand DC voltage are applied to the capacitor, the value of DCbeing chosen to raise the AC sufficiently above zero toprevent reversal. D o not raise the DC too high and exceedthe rated voltage with the peak AC.Bypass capacitors are used to prevent the flow of directcurrent without impeding the flow of alternating current.They attenuate low frequency currents while permitting

higher frequency currents to pass.The temperature at which the dielectric operates is a

The a mbient temperature in which the .capacitor isThe heat which is radiated or conducted to the capacitor.The internal heating of the capacitor due to power lossesThe physical construction and thermal conductivity of

function of the following:located.

in the conductors and dielectric.the m aterials inside the capacitor.Th e transfer of heat internally by conduction andconvection to the co ntainer.The heat lost from the container by convection,conduction, and radiation.

An increase in power factor at high temperatures maycause thermal instability and must be considered. The powerfactor is a function of temperature. The insulation resistancedecreases as the temperature increases. With polarizeddielectrics, temperature-frequency conibinations exist where

there are large increases in power factor. The capacitance ofpolarized dielectrics is a function of the temperature, voltage,and frequency. Nonpolarized dielectrics exhibit less changethan polarized ma terials.The operating temperature and changes in temperaturealso affect the mechanical structure in which the dielectric ishoused. The terminal seals utilizing elastic materials orgaskets may leak due to the set temperature characteristics.The expansion and contraction of materials with differentthermal coefficients may cause leaks at joints.Hermetically sealed units must have termina ls designed tooperate satisfactorily at the required pressure. An increase inpressure on the container of rolled capacitors in rectangularcontainers may increase the capacitance by decreasing thedistance between the conductors.Nonhermetically sealed capacitors may be susceptible tomoisture by the process of breathing. Moisture in thedielectric will decrease the dielectric strength, insulationresistance, and increase the power factor of the capacitor.Capacitors which operate in high humidities should behermetically sealed. The effect of moisture on pressurecontacts which are not gas-tight may result in a highresistance or open contact.In many applications, it is necessary to derate thecapacitor from the specifed voltage to provide the desiredperformance for the required time. Short duration transientvoltages cannot be neglected in capac itor applications.The use of the self-healing properties of certain types ofcapacitors (plastic film and tantalum), may not be desirablein circuits where intermittent failures and noise would betroublesome. At low voltages, some of these types are notself-healing.Since capacitors have inductance, the operation ofcapacitors in parallel in circuits with fast rise times ortransients may result in transient oscillations. The effectiveinductance of a large capacitor can be reduced by shunting itwith a small capacitor.Extended foil paper capacitors are considered superior tinserted tab types, having less inductance and series contact

resistance. These are important factors in low voltageapplications and in low signal-to-noise ratio circuits.The stored energy in capacitors can be dangerous topersonnel and equipment and suitable precautions should betaken to discharge ca pacitors.

1156


3/7

Trimmer capacitors fall into three categories: multi-turn,single-turn, and compression types. Multi-turn capacitors useeither glass, quartz, sapphire, plastic, or air dielectrics.Single-turn devices use ceramic, plastic, or air dielectrics.Comp ression types use a mica dielectric.For trimmer capacitor applications requiring low loss, ahigh Q (Quality Factor), stability, and tuning sensitivity; aglass, quartz, or air dielectric should be selected. Glass andquartz devices are used at frequencies up to 300 MH Z Airdielectrics are usable to about 1 GHz. For the frequencies of1 GHz or above, sapphire dielectrics offer the bestperformance. Trimmer capacitors with ceramic and plasticdielectrics are inexpensive, with high grade p lastic dielectricdevices usable at frequencies up to 2 GHz.

CERAMIC

Ceramic capacitor dielectric is made from powered b ariumtitanate. Disc elements are pressed in dies and then fired athigh temperature to produce a very dense structure. Single-plate elements are cut from larger sheets of the fired ceramicmaterial. The monolithic ceramic capacitor requires amore sophisticated design with the ceramic material actingas both the dielectric and as the encapsulant of the basicelement. The electrodes are buried within the ceramic andexit only on the ends. Up to 80 or more electrodes might beused lo obtain large values of capacitance. The wholeassembly is compressed and then fired. During firing, theceramic becomes one h omogeneous structure from which thename monolithic.There are inany ceramic dielectric formulations used toobtain special characteristics of the finished capacitor.Stability of capacitance with respect to temperature andvoltage are sacrificed when large values of K are sought.While many special formulations of capacitors are sold, theindustry is concentrating on three temperature compensatingareas: stable NPO or COG), semistable (X7R), and generalpurpose (Z5U).The Electronic Industries Association PI A ) and themilitary have established categories to divide the basic

characteristics into specified classes. Temperaturecompensating capacitors are a Class 1 capacitor. They have apredictable temperature coefficient (TC) and do not have anaging characteristic. They are the most teniperature stablecapacitor available. The TC's of Class 1 temperaturecompensating capacitors are usually N P O (negative - positive0 ppm/OC). Other Class 1 extended temperaturecompensating capacitors are also manufactured.

Semistable and general purpose capacitors with nonlineartemperature coefficients are called Class 2 capacitors. Theyhave become extremely popular because of the highcapacitance values available in very s mall size. In specifLingcapacitance change with temperature for Class 2 materials,EIA expresses the capacitance change over an operatingtemperature range by a three-symbol code. The first symbolrepresents the cold end of the temperature range. The secondsymbol represents the upper limit of the operatingtemperature range. The third symbol represents thecapacitance change allowed over the operating temperaturerange. Below is a chart illustrating a detailed explanation ofthe EIA system.

EIA CODE CHARTPercent Capacity Change Over Temperature RangeTemperature Rangeode

x7xY5

-55C to +125 C-55OC to +85 C-30C to +85 C+lO C to +85 CCodeDEFPRSTUV

Percent Capacity Change*3.3%*4.7*7.5*lo%115*20%

+22%, -33%+22%, -56+22%, -82%

Ceramic capacitors are primarily designed for use where asmall physical size with large electrical capacitance and highinsulation resistance is required. Ceramic capacitors aresmaller than paper or mica units of the same capacitance andvoltage rating. Ceramics can be used where mica or papercapacitors have too w ide of a capacitance tolerance.Temperature compensating capacitors N P O or COG) arerecommended for use in frequency determining circuits.

They can be used in any precision-type circuit where theircharacteristics are suitable. Typical applications include:oscillator, radio frequency (RF), and intermediate frequency(IF) circuits for impedance matching in frequency coupling,LC and RC tuned circuits and filters, communication tuners,and active filters.

1157


4/7

Semi-stable and general purpose ceramic capacitors arenot intended for precision applications. They are suitable forbypass, blocking, filter, and noncritical coupling elements inhigh frequency circuits; and also where changes incapacitance, caused by temperature variations, can betolerated. These capacitors are not recommended for usedirectly in frequency determining circuits. Typicalapplications include: resistive-capacitive coupling for audioand radio frequency; RF and intermediate frequency cathodebypass; tone compensation; automatic volume controlfiltering; volume control RF bypass; antenna coupling; andaudio-plate RF bypass.Variable ceramic capacitors are small sized trimmercapacitors designed for use where fine tuning adjustmentsare periodically required during the life of the equipment.They are used for trimming and coupling in such circuits sintermediate frequency, radio frequency, oscillator, phaseshifter, and discriminator stages.Across-the-line ceranuc capacitors should be safety agencya,SA, etc.) approved. The capacitors must comply withthe appropriate standard for the application, such as across-the-line, antenna isolation, or line-bypass.

PLASTIC FILMThe original film capacitors did not use plastic film, but

paper. As the various synthetic plastic materialsparticularly the thermoplastic materials were developed,their superiority over paper for most applications becameapparent. Usually, only one type of plastic film is used in anygiven capacitor, although mixtures of two different plastics,or plastic and paper, or plastic and impregnated paper, areall possibilities.The plastic dielectric material is sandwiched bdween twopieces of metal foil which become the electrodes. More thanone piece of plastic film can be used to comprise thedielectric because there a re always chances of pinholes in theplastic. The odds against having two pinholes line upopposite one another are very small. To contain this structure

in a practical space, the sandwich is wound into a jelly rolland then tightly anchored. Once the jelly roll is wound up,the nest step is connecting wires to the two electrodes andthen encasement,Another major class of plastic film capacitors is known asmetallized film. Th is design offers a much higher

volumetric efficiency. The electrodes are vacuum-depositedon the dielectric film, and their thickness might be 1/100 ofthat of foil electrodes. Th e thinner electrodes save space, andthe resistance of the foil electrode is higher.The metallized capacitors have a self-healingcharacteristic called clearing. Th e metallic film imposedon the plastic is very thin a nd if a breakdown by either a holeor contaminant occurs, a tiny area of the thin filmsurrounding the breakdown point burns away. This leavesthe capacitor operable, but with a slightly reducedcapacitance. In the conventional plastic foil type (where thefoil is thicker), sustained conduction c n occur on abreakdown causing a large area of the plastic surroundingthe breakdown to be carbonized resulting in a permanentshort-circuit. In digital circuits, it is very possible that the

flow of current during the clearing action would cause aspurious signal and upset the logic of the circuit,The present drive towards miniaturization, closerelectrical tolerances, and higher operating temperatures isbeing met by the use of thin plastic film dielectrics in theconstruction of capacitors. Th e greatest advantage of plasticfilm dielectrics over natural dielectrics (such s paper andmica) is that the plastic film is a synthetic that can be madeto meet specific requirements (such as thickness of dielectricand high-heat resistance).Many plastic film capacitors are not impregnated but arewound and encased dry. Plastic dielectric capacitors haveinsulation resistance values far in excess of those for paperand since they are nonabsorbent. Their moisturecharacteristics are superior to those of mica.Plastic film capacitors may be used where an ACcomponent is present and the impressed voltage is smallwith respect to the DC voltage rating.Film capacitors are suited for filters, m ultivibrator timingcapacitors, Ax converters, integrators, and otherapplications where capacitance stability is essential.Film capacitors have many outstanding electricalcharacteristics and excellent volumetric efficiencies, up to 20times greater than mica, glass, and porcelain.

ALUMINUM ELECTROLYTIC

The aluminum electrolytic capacitor can obtain highcapacitance in a sma ll space. The capacitor is constructed ofan aluminum foil ribbon, on the surface a thin film ofaluminum oxide has been formed electro-chemicallv. and a

1158


5/7

water-based electrolyte fluid which acts as tlie opposingplate. The oxide-coated foil, a second strip of aluniinuin foil(for connection with tlie negative plate electrolyte which isusually bonded to tlie aluminum can that houses thecapacitor), and a porous strip of paper interposed betweenthem are rolled up together and suspended in the liquidelectrolyte which penetrates tlie porous paper. The porousstrip prevents direct short circuits between the two foil strips.The metal cases for these capacitors are provided with aninsulating sleeve. It should be noted that the insulatingresistance refers to the sleeve and not to tlie resistancebetween tlie terminal and tlie case.Multi-tabbing of tlie foil windings has the effect ofconnecting tlie resistance of the segments in parallel, therebyreducing the total resistance of the foil ribbon and lower theESR (Equivalent Series Resistance). For most effectiveminiiiiization of ESR and ESL (Equivalent SeriesInductance), the tabs must be placed in the exact

mathematical center of each segment. This placem ent is nowaccomplished by computerized techniques which locate thetabs for optimum electrical performance and for mechanicalease of assembly. Another benefit of tlie multi-tabbingtechniques is greater capacitance in low voltage units.Useful life expectancy is a function of the rate ofelectrolyte loss by means of vapor transmission through theend seal. Electrolyte loss through the end seal does occurduring shelf storage and during periods of low voltage stresswhen in operation.While tlie energy storage capabilities of tlie aluminumelectrolytic capacitors are impressive, electrolytic

construction has certain inherent limitations that affect theuse and perforniance of these capacitors. S,afe operatingvoltages are limited. The oxide dielectric has rectifierproperties by blocking current flow in one direction butoffering low resistance in the opposite direction; it istherefore limited to DC applications, and a voltage reversalof more that a volt or two will cause breakdown of the filmand destruction of the capacitor.Nonpolarized types for AC applications are available. Intheir construction, both foils are coated with oxide dielectric,constituting two capacitors connected back-to-back. Thepower factor of electrolytics is coiisiderably higher thanthose of other capacitor types and the broad plate area makesfor appreciable leakage.

compact container.Aluminum electrolytic capacitors are intended for use infilter, coupling, and bypass applications where pulsating, lowfrequency, DC signal components are to be filtered out. Alsogood for applications where excesses of capacitance over thenominal value can be tolerated.Polarized capacitors should only be used in DC circuitswith polarity properly observed. If AC components arepresent, the sum of the peak AC plus the applied DC voltageshould never exceed the DC rating. The peak AC valueshould be maintained, even on negative peaks to avoidoverheating and damage. Capacitors which have beensubjected to voltage reversal should be discarded.Nonpolarized capacitors should be used in application wherereversal of potential occurs.Aluminum electrolytic capacitors are not suitable for

airborne equipment applications since they should not besubjected to low barometric pressure and low temperatures athigh altitudes. Even though they have vents designed to openat dangerous pressures, explosions can occur because of gaspressure of a spark ignition of free oxygen and hydrogenliberated at the electrodes. Provisions should be made toprotect the surrounding parts.The perform ance of capacitors at subzero temperatures isprimarily affected by an increase in series resistance and acapacitance decrease. These cha nges do not persist with thereturn of normal temperature conditions.AC motor-start capacitors are often nonpolar aluminum

electrolytic capacitors designed for intermittent C duty; thestarting of AC m otors. They are not suitable for most DC orcontinuous AC applications. The life expectancy of thecapacitor is directly proportional to the capacitor's dutycycle.Vertical mounting of the AC motor start capacitor withthe terminals up is recommended; however, horizontalmounting with the pressure relief vent up is acceptable.Vertical mounting with the terminals down or horizontalmounting with tlie relief vent down is not recommended asthey may reduce capacitor life and could impair theoperation of the pressure relief vent. Misapplication, such sexceeding design limits or applying continuous A C voltage,may result in destruction or explosion of capacitors.

Aluminum electrolytic capacitors provide the smallestvolume, mass, and cost per microfarad of any type ofcapacitor with the esceptioii of the tantalum electrolyticcapacitor. They provide tlie equipment designer with Tantalum electrolytics have become the preferred typeunusually lightweight components of high capacitance in a where high reliability and long service life are paramount

TANTALUM

1159


6/7

considerations. Tantalum is not found in its pure state. Wet-slug capacitors primary use is in low voltage powerTantalum is found in a number of oxide minerals. After supply filtering circuits. Their leakage current is the lowesttantalum is mined, it goes through an extraction processing of all tantalum types. They are ideal for filter, bypass,which, at elevated temperatures, reduce the oxide to coupling, and timing applications for power supplies,tantalum powder. Manufacturers use tantalum wire and foil, computers, telecommunications, instrumentation, andboth of which are made from the powder. Pressed and fired control systems. They are not suitable for applicationsslugs of the powder are used as capacitor elements. involving any voltage reversal.Tantalum capacitors contain either liquid or solidelectrolytes. The liquid electrolyte in wet-slug and foilcapacitors, generally sulfuric acid, forms the cathode(negative) plate. In solid electrolyte capacitors, a drymaterial, manga nese d ioxide, foriiis the cathode plate. Thereare three types of tantalum electrolytic capacitors: foil, wet-slug, and solid.Tantalum foil capacitors have the lowest capacitance perunit volume of the three types. It is best suited for the highervoltages arid is more expensive thus used only where neither

a wet-slug or solid tantalum capacitor can be used.Wet-slug tantalum capacitors are a tantalum pelletinserted into a tantalum or silver can which contains anelectrolyte solution. Most liquid electrolytes are gelled toprevent the free movement of the solution. A suitable endseal arrangement prevents the loss of electrolyte.The solid tantalum (sometimes called a dry tantalumcapacitor) uses nianganese dioxide rather than a liquidelectrolyte as an electrode. Leads are attached to thetaritalum pellet and then encapsulation by dipping the pelletin liquid epo'xy resin. Th is offers escellen t reliability andhigh stability for coilsumer and commercial electronics

applications, with the added feature of low cost.Etched-foil types have as much as 10 times thecapacitance per unit area as the plain-foil types for a givensize. The etched-foil type is generally the better choicebetween the two.Polarized foil types are used where low frequencypulsating DC coinponents are to be bypassed or filtered out.Other uses include electronic equipment where largecapacitance values are required and wide capacitancetolerances can be tolerated.

Nonpolarized foil capacitors have two polarized sections,with their cathodes connected back-to-back, and theninserted in an outer enclosure. They are suited for ACapplications or where DC voltage reversals occur. Examplesare: tuned low frequency circuits, phasing of low voltage ACmotors, computer circuits where reversal of DC voltageoccurs, and servo systems.

Solid tantalum capacitors are the most stable and reliableelectrolytics available, having a longer life characteristicthan any of the o ther electrolytic capacitors. Because of theirpassive electrolyte being solid and dry, these capacitors arenot temperature sensitive and have a lower capacitance-temperature characteristic than any of the other electrolyticcapacitors. The limitations include: high leakage current,limited voltage range available, and an allowable reversevoltage.Solid tantalum capacitors are mainly designed for filter,

bypass, energy storage, coupling, blocking, and other lowvoltage DC applications (such as transistor circuits inmissile, aircraft electronics, and computers) where stability,size, weight, an d shelf-life are important factors.Tantalum ch ip capacitors are for use in thick and thin filmhybrid circuits and for surface mounting. The tantalum chipcapacitor has no encapsulation but has ter minals designed tosolder directly onto ceramic substrates. The solid tantalumcapacitor possess a unique healing mechanism whichresults in a failure apparently decreasing forever.

GLASSGlass dielectric capacitors offer the highest performanceand reliability features available in the capacitor industry.The glass dielectric is formed s a continuous ribbon ofglass. The capacitors are composed of alternate layers ofglass ribbon and the aluminum electrode material. Afterassembly, the units are sealed together by high temperatureand pressure to form a rugged monolithic block. Since theterminal leads are fused to the glass case, the seal cannot bebroken without destroying the capacitor. The block may beenclosed in glass or enamel cases to suitably protect againstenvironmental cond itions.Glass is very stable, doesn't corrode or degrade in anyway, highly resistant to high operating temperatures, voltagebreakdown, and nuclear radiation. Glass capacitors arecapable of withstanding environmental conditions of shock,vibration, acceleration, extreme moisture, vacuum, and havean extended life of more than 30 000 hours.

1160


7/7

Glass capacitors are useful where failures are notacceptable, such as satellite systems, undersea cablerepeaters, and mountain-top microwave relay stations. Thelarge RF currents that glass capacitors can handle makethem ideal for use in modulators, filters, and linearamplifiers.

Glass capacitors have a high Q factor and a lowdissipation factor that changes little with frequency andtemperature. They exhibit zero aging rate, zero piezoelectricnoise, zero voltage coefficient, and low thermal and chargenoise figures. Glass capacitors are effective substitutes formica capacitors if consideration is given to the differences intemperature coefficient and dielectric loss,In general, glass capacitors are ideally suited for anyeiiviroiiinen t where high tem perature cou ld alter or destroycircuit performance and where cycling to coldertemperatures may be a problem.

MIC

Muscovite mica is the most coininonly used micadielectric material. Muscovite riiica can be split into thinsheets, it is nonporous and does not readily absorb moisture.Although protection from moisture is provided to obtaincapacitance stab ility an d low losses.The two techniques to form the capacitors are by stackingthe mica sheets through the silvered-mica process or by theuse of tin-lead foil to separate the mica sheets. Terminals areattached to the m ica stacks by the use of p ressure clips which

have been solder coated for maxinium mechanical strength.Button style mica capacitors arc composed of a stack ofsilvered-mica sheets connected in parallel. This assembly isencased in a metal case with a high potential terminalconnected through the center of the stack. The other terminalis formed by this metal case connected at all points aroundthe outer edge of the electrodes. The units are then weldedand hermetically sealed with either glhss or resin. Themolded case is made of a polyester material which alsoexhibits high insulation resistance and high resistance tomoisture absorption and transmission. The button styledesign permits the current to fan out i n a 360 pattern fromthe center terminal. This provides the shortest RF current

path between the center terminal and chassis. The internalinductance is also kept small.

frequency filtering, bypassing, and coupling. Examples arein tuned circuits which control frequency, reactance, orphase; delay lines, and stable low power networks.Button style capacitors are intended for use at frequencies

up to 500 MHz. Their principal uses are in tuned circuits,and for the coupling and bypassing applications in VHF andUHF circuits.Failure of button style capacitors is due to silver ionmigration. Silver ion migration can occur in on ly a fewhours when silvered-mica capacitors are used undersimultaneously DC voltage stresses combined with exposureto continuous high temperature and humidity conditions.

SUMMARYReliab ility is a measure of the expected failure rate duringthe useful life of the capacitor. The cost of a capacitor withan extremely long useful life may not be justified if the endproduct has a short useful life. The degree of reliability,therefor e, is predicated on the planned life of the endequipment. When more than one type of capacitor may beused in a given application, consideration should then begiven to cost, availability, and allowable space.

REFERENCE:1. Cletus J. Kaiser, THE CAPACITOR HANDBOOK,Second Edition, Second Printing, CJ Publishing, 1997.

The characteristics of mica dielectric are high insulationresistance and high breakdown voltage low power factorlow inductance, and low dielectric absorption. Micacapacitors are designed for the circuits requiring precise

1161

Documents

00730293 Capacitors-Various Dielectrics and Their Applications