Two conductors close to each other are sandwiched with a layer of non-conductive insulating medium, which constitutescapacitor。When a voltage is applied between the two plates of a capacitor, the capacitor will store electric charges.The capacitance of a capacitor is numerically equal toCharge quantityThe ratio to the voltage between two plates.Capacitance of capacitorBasic unityesFarad(F)。stayCircuit diagramThe letter C is usually used inCapacitive element。[1]
Capacitor is used to store electric quantity and energy（Electric potential energy）Components of.Surrounded by or emanating from one conductorElectric field lineA conductor system that terminates entirely in another conductor is called a capacitor.[3]
General formula C=Q/U, special formula for parallel plate capacitor: electric field intensity between plates E=U/d.[3]
Main parameters of capacitor
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(1)nominalCapacitance, is the capacitance marked on the capacitor.However, the actual capacitance of the capacitor is less than
Capacitance charging process
The nominal capacitance is biased,Accuracy classAndAllowable errorThere is correspondence.General capacitors are commonly used at levels I, II and III, and electrolytic capacitors are used at levels IV, V and VI to indicate capacity accuracy, which shall be selected according to the purpose.The capacitance of electrolytic capacitor depends onAC voltageThe impedance presented when working under theworking frequency , temperature, voltage andmeasuring methodThe capacitance value will change with the change of.The unit of capacitance is F (method).[4]
AC circuit with pure capacitance[17]
Since capacitor is a kind of "container" for storing charge, there is a problem of "capacity".In order to measure the capacity of the capacitor to store charge, the capacitancephysical quantity。Capacitors can store charge only under the action of applied voltage.Different capacitors stored under voltageCharge quantityIt may also be different.It is internationally unified to add 1 volt to the capacitorDC voltageThe amount of charge it can store is the capacitance of the capacitor (i.e., the electricity quantity under unit voltage), which is represented by the letter C.CapacitiveBasic unitIs Farad (F).Under the action of 1 volt DC voltage, if the charge stored in the capacitor is 1 coulomb, the capacitance is determined as 1Farad, Farad is represented by the symbol F,1F=1Q/V。In practical applications, the capacitance of a capacitor is often much smaller than 1 farad, and usually smaller units, such as millifarad (mF)Microfluid(μ F), nano method (nF)Skin method(pF), etc. Their relationship is: 1 microf is equal to one millionth of a farad;1 Pifa is equal to one millionth of microffa, namely:[5]
(2)Rated voltage, is at the lowestambient temperatureThe maximum DC voltage that can be continuously applied to the capacitor at rated ambient temperature.Ifworking voltage If the withstand voltage of the capacitor is exceeded, the capacitor will be broken down, causing damage.In practice, with the increase of temperature, the withstand voltage value will become lower.[4]
(3)insulation resistance 。DC voltage is applied to the capacitor to generateLeakage current The ratio of the two is called insulation resistance.When the capacitance is small, its value mainly depends on thesurface state ；When the capacity is greater than 0.1 μ F, its value mainly depends on the medium.Generally, the greater the insulation resistance, the better.[4]
(4) Losses.Under the action of electric field, the capacitanceinternal causefeverThe energy consumed is called loss.Loss vsfrequency range , Mediaconductance, resistance of metal part of capacitor, etc.[4]
(5)frequency characteristic。With the increase of frequency, the capacitance of general capacitors presents the law of decline.When the capacitor works atresonant frequency When below, it is capacitive;When the resonance frequency is exceeded, it is inductive. At this time, it is not a capacitor but an inductor.Therefore, it must be avoided that the capacitor works above the resonant frequency.[4]
effect
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capacitor
stayDC circuitThe capacitor is equivalent to an open circuit.Capacitor is a kind of component that can store electric charge, and it is also one of the most commonly used electronic components.[6]
It starts from the structure of the capacitor.The simplest capacitor is composed of plates at both ends and insulation in the middledielectric(including air).After electrification, the electrode plate is electrified, forming a voltage (potential difference), but because of the insulating material in the middle, the entire capacitor is non-conductive.However, in this case, the capacitor is not exceededCritical voltage（breakdown voltage ）Under the precondition of.We know that any substance is relatively insulated. When the voltage at both ends of the substance increases to a certain extent, the substance can conduct electricity. We call this voltage breakdown voltage.The capacitance is no exception. After the capacitance is broken down, it is notinsulatorHas.However, in the middle school stage, such voltage is not visible in the circuit, so it works under the breakdown voltage and can be seen as an insulator.[6]
But, inAC circuitBecause the direction of current changes as a function of time.The process of capacitor charging and discharging takes time. At this time, a changing electric field is formed between the plates, and this electric field is also a function of time.In fact, current flows between capacitors in the form of an electric field.[6]
●wave filtering: Used infilter circuit The capacitor in is calledFilter capacitor, power filter and variouswave filterThis kind of capacitor circuit is used in the circuit. The filter capacitor removes the signal within a certain frequency band from the total signal.[6]
●DecouplingThe capacitor used in decoupling circuit is calleddecoupling capacitors , onMultistage amplifierOfDC voltageThis kind of capacitor circuit is used in the supply circuit, and the decoupling capacitor eliminates the harmful low-frequency interaction between each amplifier stage.[6]
● High frequencyVibration damping: The capacitor used in high-frequency vibration elimination circuit is called high-frequency vibration elimination capacitorNegative feedback amplifierIn order to eliminate vibrationHigh frequency self excitationThe capacitor circuit is used to eliminate the possible high frequency of the amplifierHowl。[6]
●resonance: The capacitor used in LC resonant circuit is called resonant capacitor, and LC parallel connection andSeries resonanceThis kind of capacitive circuit is required in the circuit.[6]
●bypass: Used inbypass circuitThe capacitor in is calledBypass capacitanceIf the signal of a certain frequency band needs to be removed from the signal in the circuit, the bypass capacitor circuit can be usedsignal frequency Different, completefrequency domain(AllAC signal）Bypass capacitor circuit and high-frequency bypass capacitor circuit.[6]
●timing: The capacitor used in timing circuit is called timing capacitor.When it is necessary to charge and discharge the capacitortime controlThe timing capacitor circuit is used in the circuit oftime constantThe role of size.[6]
● Points: used inIntegrating circuitThe capacitors in are called integral capacitors.In the synchronous separation circuit of potential field scanning, the integration capacitor circuit can be used to realize the recombination from the fieldSynchronizing signalTake the field synchronization signal.[6]
●differential: Used inDifferential circuitThe capacitor in is calledDifferential capacitance。staytriggerIn order to obtain the tip trigger signal, this differential capacitance circuit is used to generate the trigger signal from various types of (mainlyRectangular pulse）The spike pulse trigger signal is obtained from the signal.[6]
● Compensation: The capacitor used in the compensation circuit is called the compensation capacitor. In the bass compensation circuit of the card holder, this low-frequency compensation capacitor circuit is used to enhance the low-frequency signal in the playback signal. In addition, there is a high-frequency compensation capacitor circuit.[6]
● Bootstrap: forBootstrap circuitThe capacitor in is called bootstrap capacitor, and the common OTLpower amplifierThe output stage circuit uses this bootstrap capacitor circuit to passpositive feedbackThe positive half cycle amplitude of the signal will be slightly increased in the way of.[6]
●frequency division: onFrequency dividing circuitThe capacitor in the loudspeaker is called frequency dividing capacitorspeakerIn the frequency dividing circuit, the frequency dividing capacitor circuit is used to make the high-frequency loudspeaker work in the high frequency band, the mid-range loudspeaker work in the middle frequency band, and the low-frequency loudspeaker work in the low frequency band.[6]
●Load capacitance: refers toQuartz crystal resonatorThe effective external capacitance that together determines the resonant frequency of the load.Commonly used for load capacitanceStandard valueThere are 16pF, 20pF, 30pF, 50pF and 100pF.The load capacitance can be properly adjusted according to the specific situationresonatorThe operating frequency of is adjusted toNominal value。[6]
model
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Model designation
The model of domestic capacitor generally consists of four parts (not applicable to voltage sensitive, variableVacuum capacitor）, respectively representing name, material, classification and serial number.[7]
Part I: Name, indicated by letter, capacitor is C.[7]
Part II: Materials, represented by letters.[7]
Note: A-tantalum electrolysis, B-polystyrene and other non-polar films, C-high-frequency ceramics, D-aluminum electrolysis, E-other materials electrolysis, G-alloy electrolysis, H-composite medium, I-glass glaze, J-metallized paper, L-polyester and other polar organic films, N-niobium electrolysis, O-Glass filmQ - paint film, T - low-frequency ceramics, V-Mica paper, Y-mica, Z-paper.[7]
Part III: Classification, generally expressed in numbers, and individually expressed in letters.[7]
Note: T - electric iron, W - fine adjustment, J - metallization, X - small, S - single stone, D - low pressure, M - sealing.[8]
The figures are shown as follows:[9]
model
Symbol
Porcelain intermediate
mica
Organic
electrolysis
one
circular
Unsealed
Unsealed
Foil type
two
Tubular
Unsealed
Unsealed
Foil type
three
Lamination
seal up
seal up
Sintering powder liquid
four
Monolith
seal up
seal up
Sintering powder liquid
five
pierce the heart
/
pierce the heart
/
six
Strut shape
/
/
/
seven
/
/
/
Nonpolarity
eight
high pressure
high pressure
high pressure
/
nine
/
/
special
special
Part IV: Serial number, expressed by numbers or letters.[7]Including variety, size code, temperature characteristics, DC working voltage, nominal valueAllowable errorStandard code.[8]
Capacity label
method
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Example
Direct calibration method
Mark directly with numbers and unit symbols.
As 1
Represents 1 micro method, and some capacitors are represented by "R"decimal pointFor example, R56 represents 0.56 microf.[10]
Character symbol method
Use numbers andText symbolsRegular combination to represent capacity.
For example, p10 represents 0.1pF, 1p0 represents 1pF, 6P8 represents 6.8pF, and 2u2 represents 2.2uF.[10]
Color scale method
useColor ringorColor spotRepresents the main parameters of the capacitor.The color scale method of capacitor is the same as that of resistance.[10]
2. Large capacity error,leakage current Large;Ordinary ones are not suitable for high frequency and low temperature applications, and should not be used at frequencies above 25kHz.[11]
Sintered tantalum block is used as cathode, and solid electrolyte is usedmanganese dioxide。temperature characteristic 、frequency characteristicAnd the reliability is better than that of ordinary electrolytic capacitors. Especially, the leakage current is very small, the storage is good, the life is long, the capacity error is small, and the volume is small. The maximum capacitance voltage product can be obtained under the unit volume.Its tolerance to pulsating current is poor, and it is easy to be short circuited if damaged.It is often used in ultra small and highly reliable parts.[11]
Self-healing shunt capacitor
The structure is similar to that of paper capacitor, but polyesterpolystyreneEqual low loss plastic material as medium.The characteristics are as follows:[11]
One of its electrodes is the mounting screw.The lead inductance is very small, the frequency characteristic is good, and the dielectric loss is small,With temperatureCompensatory effect。[11]
1. It cannot be made into a large capacity, because vibration will cause capacity change.[11]
2. Especially suitable for high-frequency bypass.[11]
In several piecesCeramic filmThe billet is covered with electrode paddle material, which is wound into an indivisible whole after lamination, and then wrapped with resin outside.It is a new type with small volume, large capacity, high reliability and high temperature resistancecapacitor。highDielectric constantLow frequency ofMonolith capacitorIt also has stable performance, small volume and large capacity error.Generally, two aluminum foils are used as electrodes, and 0.008-0.012mm thickCapacitor paperIt is winded by separating and overlapping.manufacturing processSimple, cheap, can get a larger capacitance.[11]
Metallized polypropylene capacitor
Generally, it is in the low-frequency circuit, and generally cannot be higher than 3~4MHzFrequency.Oil immersionThe withstand voltage of capacitor is higher than that of ordinary paper capacitor, and the stability is also good, which is suitable forHigh voltage circuitTrimmer capacitor(Semi variable capacitor）The capacitance can be adjusted within a small range, and can be fixed to a certainCapacitance value。[11]
Ceramic trimming capacitorCharge quantityIt is high and small in size, and can be generally divided into two types: round tube type and round disc type.The mica and polystyrene media are usually spring type, with simple structure but poor stability.The wire wound ceramic fine tuning capacitor is used to change the capacitance by removing the copper wire (outer electrode), so the capacity can only be reduced, and it is not suitable for use in situations requiring repeated debugging.[11]
Ceramic capacitor
Using high dielectric constantCapacitor ceramics〈barium titanateTitanium monoxideExtruded tube formingWaferOr the disc is used as the medium, and silver is plated on the ceramic by the burning infiltration method as the electrode.It is also divided into high-frequency and low-frequency porcelain.With small positiveCapacitance temperature coefficientCapacitor for high stabilityOscillation loopAs the loop capacitor and the padding capacitor.[11]
Low frequency porcelain capacitor is limited toworking frequency It is used for bypass or DC isolation in lower circuits, or where stability and loss requirements are not high (including high frequency).This capacitor should not be used inPulse circuitMedium, because they are easily pulsedvoltage breakdown 。[11]
High frequency porcelain capacitor
Applicable toHigh frequency circuitmica condenserIn terms of structure, it can be divided into foil type and quilt type.The silver electrode is directly connected to theMica sheetUpper useVacuum evaporation methodOr silver layer is plated by burning infiltration methodAir gap，temperature coefficientThe capacitance stability is also higher than that of foil type.Good frequency characteristics, high charge value, small temperature coefficient, can not be made into large capacity.Widely used in high-frequency electrical appliances, and can be used asStandard capacitor。[11]
Glass glaze capacitor
It is made by spraying a special mixture with a concentration suitable for spraying into a thin film, and the dielectric is sintered into a "monolith" structure with silver layer electrodes. Its performance is comparable to that of mica capacitors, and it can withstand variousClimatic environment, generally working at 200 ℃ or higher, ratedworking voltage Up to 500V.[11]
Detection method of fixed capacitor
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1. Detect small capacitance below 10pF:Fixed capacitorThe capacity is too small, useA multimeterThe measurement can only qualitatively check whether there is leakage, internal short circuit or breakdown.During measurement, the R × 10k gear of the multimeter can be selected, and two probes can be used to connect two pins of the capacitance at random. The resistance value should beInfinity。If the measured resistance value (the pointer swings to the right) is zero, it indicates that the capacitor is damaged by leakage or internal breakdown.[12]
2. Detect 10PF~001 μ F fixed capacitor: judge whether it is charged, and then judge whether it is good or bad.R × 1k gear is selected for the multimeter.TwotriodeThe β value of is more than 100, andThrough currentSmall.It can be composed of 3DG6 and other silicon triodesComposite pipe。The red and black probes of the multimeter are respectivelyEmitterE andcollectorC phase.Due to the amplification effect of the compound triode, the charging and discharging process of the measured capacitance is amplified, so that the pointer swing of the multimeter is increased, which is convenient for observation.[12]
It should be noted that during the test operation, especially when measuring the capacitance of smaller capacity, the pin of the measured capacitance should be repeatedly replaced to contact A and B, so that the pointer of the multimeter can be clearly seen swinging.For the fixed capacitance above 001 μ F, the R × 10k gear of the multimeter can be used to directly test whether the capacitor has charging process, internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.[12]
Charge and discharge
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(1) Charging process.
The process of charging the capacitor (storing charge and electric energy) is called charging.Connect one electrode plate of the capacitor to the positive pole of the power supply and the other electrode plate to the negative pole of the power supply, and the two electrode plates will carry the same amount of heterogeneous charges respectively.After charging, there is an electric field between the two plates of the capacitor. During the charging process, the electric energy obtained from the power supply is stored in the capacitor.[13]
(2) Discharge process.
The process of making the charged capacitor lose charge (releasing charge and electric energy) is called discharge.For example, if a wire is used to connect the two poles of a capacitor, the charges on the two poles will neutralize each other, and the capacitor will release charges and electric energy.After discharge, the electric field between the two plates of the capacitor disappears, and the electric energy is converted into other forms of energy.[13]
Battery self discharge refers to the ability of the battery to maintain the stored charge in the open circuit state.Lithium ion batteryThe type of self discharge can be divided into physical self discharge and chemical self discharge.The single battery forms the module by series connection and parallel connection. If the self discharge consistency of the single battery in the module is poor, the internal single terminal voltage of the module will be inconsistent after storage for a period of time, resulting in the phenomenon that some single battery has reached the target voltage during the charging and discharging process of the module, while the other single battery is still at a higher or lower voltage, resulting in the single batteryOverchargeorOver discharge, and even producesafety problemThis is also a challenge to the module voltage balance capability.Self discharge isLithium ionAn important part of capacitorperformance index 。[18]
Troubleshooting
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1. Common faults of capacitor.The power supply shall be cut off immediately when one of the following conditions of the capacitor is found.[14]
(1) When the capacitor explodes and catches fire, immediately disconnect the power supply and use sand and dry typeFire ExtinguisherFire fighting.[14]
(2) When the fuse of the capacitor is blown, it shall be reported to the dispatcher, and the capacitor shall be opened after obtaining the consentCircuit breaker。Cut off the power supply and discharge it firstExternal inspectionIf there are flashover marks on the outside of the casing, if the casing is deformed, if there is oil leakageGrounding deviceYes NoShort circuit phenomenonAnd shake to measure the insulation resistance between poles and pole to ground, and checkCapacitor bankWhether the wiring is complete and firm, and whether there is phase loss, such asNot foundThe failure phenomenon can be put into operation after the insurance is replaced.If the fuse is still fused after power transmission, the fault capacitor shall be exited and power transmission to the rest shall be resumed.If the circuit breaker trips at the same time as the fuse is blown, do notForced delivery。It shall be put into operation after the above inspection is completed and the insurance is replaced.[14]
(3) If the circuit breaker of the capacitor trips but the shunt fuse is not broken, discharge the capacitor for three minutes before checking the circuit breakerCurrent transformerpower cable And capacitor exterior, etc.If no abnormality is found, it may be due to external fault busvoltage fluctuationCaused by.After inspectionTrial investment；Otherwise, further comprehensive power on test shall be conducted for the protection.Through the above inspection and test, if the cause is still not found, it is necessary to act according to the system and gradually test the capacitor.No trial investment is allowed until the cause is found out.[14]
3. When handling faulty capacitorSafety matters。Because the two poles of the capacitor have residualResidual chargeTherefore, first of all, try to discharge all its charges, otherwise electric shock accidents may occur.When dealing with faulty capacitors, the circuit breaker of the capacitor bank and its upper and lower parts shall be opened firstIsolating switch, if usedFuseProtection, remove it firstFuse tube。At this time, although the capacitor bank has passedDischarge resistanceSelf discharge, but there will still be some residual charges, so manual discharge is necessary.When dischargingground wireThe grounding terminal ofGrounding gridFix it and use it againEarth barDischarge the capacitor for many times until there is no spark and discharge sound, and finally fix the grounding wire.At the same time, it should also be noted that if the capacitor has internal disconnectionFuseFuse or leadpoor contactThere may also be residual charges between its two poles, which will not be discharged during automatic discharge or manual discharge.Therefore, the operation or maintenance personnel shall wear them before contacting the faulty capacitorInsulating gloves, and useShort routeShort circuit the two poles of the fault capacitor to discharge it.In addition, capacitors connected in series shall be discharged separately.[15]
For supercapacitors, there are differentclassification method 。First, according to different energy storage mechanisms, supercapacitors can be divided into two categories: electric double layer capacitors and Faraday quasi capacitors.Among them, the electric double-layer capacitor mainly generates stored energy by adsorption of pure electrostatic charges on the electrode surface.Faraday quasi capacitor is mainly made of Faraday quasi capacitor active electrode materials (such asTransition metal oxideandPolymer）Reversible oxidation-reduction reaction occurs on and near the surface to generate Faraday quasi capacitance, thus realizing energy storage and conversion.Secondly, according toelectrolyteIt can be divided into two categories: water system supercapacitor and organic system supercapacitor.In addition, it can be divided into symmetric supercapacitors and asymmetric supercapacitors according to whether the types of active materials are the same.Finally, according to the state form of electrolyte, supercapacitors can be divided intosolid electrolyteSupercapacitors and liquid electrolyte supercapacitors.[16]
In the 1960sSupercapacitorIn the late 1970s and early 1980s, large-scale commercial production of supercapacitors appeared.Super capacitors in Chinatechnological developmentIt started late. Since the 1980s, relevant enterprises, universities and research institutes have successively carried out research work related to supercapacitors. By the 1990sElectric carRapid development, as the main electric energy of electric carsStorage unitSupercapacitors are attracting more and more attention.Compared with traditional capacitors, supercapacitors have more obvious advantages.[19]
2. It is practical. Its service life is very long, and it does not need frequent maintenance.
3. Environmental protection.Compared with traditional batteries, it is environmentally friendly and does not produceSecondary pollutionTherefore, the appearance of supercapacitor provides a good solution for the storage of electric energy.
