synonymAluminum electrolytic capacitor(Industrial products) generally refers to aluminum electrolytic capacitors
Aluminum electrolytic capacitor is made of aluminum cylinder as negative electrode, which is filled with liquidelectrolyte, insert a piece of bentAluminium stripIt is made of positive pole.It also needs to go throughDC voltageTreatment to form a layer on the positive plateOxide filmDo media.It is characterized by large capacity, large leakage, poor stability, positive and negative polarity, and is suitable for power filter or low-frequency circuit.When using, the positive and negative poles should not be connected reversely.
The global aluminum electrolytic capacitor supply market is increasingly mature, mainly focusing onJapan, Mainland ChinaTaiwanAnd South Korea.From the overall industry in recent yearsCompetition patternLook, the electrolytic capacitor in JapanoutputThey began to shrink and reduce production gradually. Instead, Korean enterprises, Taiwan enterprises and Chinese mainland enterprises took their place.Before 1978, aluminum electrolytic capacitors were considered asnew and high-tech productAfter more than 30 years of development, aluminum electrolytic capacitor is no longer a high-tech product for domestic aluminum electrolytic capacitor manufacturers.From the technical point of view, the capacitors produced by some well-known domestic brands can completely replace foreign capacitors.[1]
The global output value in 2010 was 5.2 billion US dollars, the average of the past seven yearsgrowth rate4% - 5%, expected to reach 5.5 billion dollars by 2012market size By 2015, it will reach about US $6 billion.From global aluminum electrolytic capacitordate of deliveryLook, since 2010, there has been an obvious extension, which to a large extent indicates that the industry is entering a fast growth channel.
CostUpward pressureAnd the influence of downstream demand shifting towards China. In recent years, overseas well-known aluminumElectrolytic capacitorManufacturers have come to China to invest and build factories.Except Rubycon has not yet selected a location, other world-famous aluminum capacitor manufacturers have set up production bases in China, and China has naturally become the world's largest aluminum electrolytic capacitor market, with its share rising steadily.Aluminum electrolytic capacitorTraditional consumptionElectronic fieldWhile growing steadilyapplication area along withStructural transformationAndtechnical progressstayenergy saving light, frequency conversion, new energy and many other emerging fields have been expanded.countryThe 12th Five Year PlanIt is clearly put forward in: promoting large, medium and smallUrban transportation, communication, power supply, water supply and drainage and other infrastructure integration and network development.The development of these emerging fields will expand the demand space for new material products, and China's aluminum electrolytic capacitor industry, as a national key development industry, will also gain huge development space[1]
Key points of model selection
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Rated voltage
Aluminum electrolytic capacitor
aluminium electrolysiscapacitanceThe capacity and withstand voltage marked on the body are very important and are the most basic content for selecting capacitance.At actual capacitancemodel selectionIn the middle, for places with fast current changing rhythm, larger capacity should be used, but the larger the capacity is, the better. First, with the increase of capacity, the cost and volume may rise. In addition, the larger the capacity isCharging currentThe bigger,Charging timeIt will be longer.These are all to be considered in the actual application selection.
Rated working voltage:Operating temperature rangeThe capacitor works reliably for a long time, and it can withstand the maximumDC voltage。stayAC circuitMedium, pay attention to the addedAC voltageMaximumDo not exceed the DC working voltage value of the capacitor.Common fixed capacitor working voltages are 6.3V, 10V, 16V, 25V, 50V, 63V, 100V, 200V, 250V, 400V, 450V, 475V, 500V, 600V, 630V.The voltage that the capacitor actually bears in the circuit cannot exceed its withstand voltage value.
In the filter circuit, the withstand voltage value of the capacitor shall not be less than 1.42 times of the AC effective value.Another problem to be noted is the working voltagemargin Generally, it should be above 15%.
Give WaycapacitorThe rated voltage ofinternal resistanceReduce leakage current, reduce loss angle and increase service life.Although it will not be a problem to use 50V aluminum electrolytic capacitor with 48V working voltage for a short time, the service life may be reduced if it is used for a long time.
Dielectric loss
The energy consumed by capacitor under the action of electric field is usually the ratio of loss power and reactive power of capacitor, that isLoss angleOfTangent valueRepresents (in theequivalent circuit Middle, seriesEquivalent resistanceThe ratio of ESR homoreactance 1/ω C is calledTanδ，The ESR here is the value calculated at 120Hz.Obviously, Tan δ increases with the increase of measurement frequency, and increases with the decrease of measurement temperature).The larger the loss angle, the greater the loss of the capacitor. The capacitor with large loss angle is not suitable for high-frequency operation.The dissipation factor (DF) exists in all capacitors, and sometimes the DF value is expressed by the loss angle tan δ.The lower the parameter, the better.However, this parameter of aluminum electrolytic capacitor is relatively high.
Whether the DF value is high or low depends on the temperature, capacity, voltage, frequency, etc. of capacitors of the same brand and series;When the capacity is the same, the higher the withstand voltage, the lower the DF value.In addition, the higher the temperature, the higher the DF value, and the higher the frequency, the higher the DF value will be.
Overall dimensions
The overall dimensions are related to the weight and the type of connector.Single ended is radial lead type, screw is lock screw type, andSMD aluminum electrolytic capacitorEtc.As for weight, two capacitors with the same capacity and withstand voltage but different brands must have different weights when compared;The overall dimensions are more related to the housing planning.Generally speaking, capacitors with the same diameter and capacity can be replaced by those with the same height, but the mechanism interference problem should be considered when replacing the low capacitance with those with the same length.
Power interpretation
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A capacitor will generate various impedances due to its structureInductive reactance。ESREquivalent series resistanceandESLThe equivalent series inductance is a pair of important parameters, which is the basis of capacitive reactance.A capacitor with a small equivalent series resistance (ESR) can well absorb the peak (ripple) current during fast conversion compared with an external capacitor with a large capacity.The capacitor with large ESR is used for parallel connectionCost effectiveness。However, this requires a compromise between PCB area, device number and cost.
Current voltage
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It is also called ripple current and ripple voltage, which means that the capacitor can withstandRipple current/Voltage value.Ripple voltageIt is equal to the product of ripple current and ESR.
When ripple current increases, even whenESRThe ripple voltage will also increase exponentially when it remains unchanged.In other words, when the ripple voltage increases, the ripple current also increases, which is also the reason why capacitors are required to have lower ESR values.After the ripple current is superimposed, it is caused by the equivalent series resistance (ESR) inside the capacitorfeverThus affecting the service life of the capacitor.Generally, the ripple current is proportional to the frequency, so the ripple current is relatively low at low frequencies.
ratedRippleThe current is at the maximum operating temperaturedefineValue of.In practical applications, the ripple tolerance of capacitors is also usedambient temperatureIt is related to the temperature grade of the capacitor itself.The specification bibliography usually provides a maximum ripple current that can be withstood by capacitors of various temperature levels under specific temperature conditions.It even provides a detailed chart to help users quickly find out the allowable capacitance ripple to reach a certain expected service life under certain ambient temperature conditions.
Leakage current
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Aluminum electrolytic capacitor
capacitorMedia pair ofDC currentHas a largeHindrance。However, since there is a layer of gelatinous material with water on the aluminum film, it is formed again and repaired when the voltage is appliedOxide filmIt will produce a very smallLeakage currentCurrent.Generally, the leakage current will increase with the increase of temperature and voltage.Its calculation formula is roughly: I=K × CV.The unit of leakage current I is μ A, and K is constant.Generally speaking, the higher the capacitor capacity, the greater the leakage current.It can be known from the formulaRated voltageThe higher the leakage current is, the greater the leakage current is. Therefore, reducing the working voltage can also reduce the leakage current.
life
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First of all, make it clear that the aluminum electrolytic capacitor will be broken, butTime issues。There are many reasons that affect the life of capacitors,Overvoltage, reverse voltage, high temperature, rapid charging and discharging, etc. Under normal use, the biggest impact is temperature, because the higher the temperature iselectrolyteThe faster the volatilization loss is.It should be noted that the temperature here does not refer to the environment orsurface temperature , refers to aluminum foilworking temperature 。Manufacturers usually mark the capacitor life and test temperature on the capacitor body.
Since the service life of the capacitor is halved every time the working temperature of the capacitor increases by 10 ℃, do not think that the aluminum electrolytic capacitor with a service life of 2000 hours is better than that of 1000 hours. Pay attention to the test temperature to confirm the service life.Every manufacturerWith temperatureAnd lifetimeCalculation formulaThe design capacitance shall be calculated according to the actual data.What we need to know is that to improve the service life of aluminum electrolytic capacitors, first we need to reduce the operating temperature and keep away from heat sources on the PCB. Second, we need to consider using capacitors with high maximum operating temperature. Of course, the price will also be higher.
Electrolytic capacitorThe actual voltage to be borne in the circuit cannot exceed its withstand voltage value.stayfilter circuit Medium, the withstand voltage value of capacitance shall not be less than ACValid values1.42 times.When using electrolytic capacitors, pay attention not to reverse the positive and negative electrodes.Different types of capacitors should be selected for different circuits.Mica and high frequency can be selected for wiping circuitCeramic capacitor, paper dielectric, polyester, mica, electrolysis, ceramics and other capacitors can be used for DC isolation, and electrolytic capacitors can be used for filtering,bypassCapacitors such as polyester, paper, ceramics and electrolysis can be selected.Before installing the capacitor into the circuit, check whether it has short circuit, open circuit and leakage, and check itsCapacitance value。During installation, symbols such as capacitance category, capacity and withstand voltage shall be easy to see for verification.
Life estimation(life expectancy): the time for the electrolytic capacitor to operate continuously at the highest operating temperature.
Ta=actual operating ambient temperature of capacitor
Example: specification value 105 ℃/1000hrs
Life estimation at 65 ℃: lx=1000 * 2 (105-65)/10
Actual service life: 8000hrs
High temperature load life willElectrolytic capacitorInca rated at maximum operating temperatureworking voltage After a continuous specified completion time, the following changes must be met: δ cap: within 20% of the value before the test.
It should be reminded that the service life of aluminum electrolytic capacitor should refer to the life calculation formula given by the original manufacturer. Remember[2]。
impedance
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At a specific frequencyAC currentThe resistance passing through is the so-calledimpedance。It is connected with capacitorequivalent circuit The capacitance and inductance values in are closely related toESRIt also matters.CapacitiveCapacitive reactanceAt lowfrequency range With the increase of frequency, the reactance decreases to the value of ESR when the frequency continues to increase and reaches the intermediate frequency range.When the frequency reaches the high frequency rangeInductive reactanceBecomes dominant, so the impedance increases with the increase of frequency.
Output in switching power supplywave filteringElectrolytic capacitor, whichSawtooth waveThe voltage frequency is up to tens of kHz, even tens of MHzcapacitanceQuantity is not its main indicator. The standard to measure the quality of high-frequency aluminum electrolytic capacitor is the "impedance frequency" characteristic, which is required toworking frequency There should be a lower equivalent impedance in thesemiconductor device High frequency generated during operationSpike signalIt has good filtering effect.
Product features
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The first feature of electrolytic capacitor: the capacitance per unit volume is very large, tens to hundreds of times larger than other types of capacitance.
Characteristic 2 of electrolytic capacitor: the rated capacity can be very large, which can easily reach tens of thousands of μ f or even several f (but cannot be compared withElectric double layer capacitorRatio).
The third feature of electrolytic capacitor is that its price has an overwhelming advantage over other types, because the constituent materials of electrolytic capacitor are ordinary industrial materials, such as aluminum, etc.The equipment for manufacturing aluminum electrolytic capacitors is also commonindustrial equipment , Yesmass production The cost is relatively low.
