Low ESR aluminum electrolytic capacitor
Electrolytic Capacitors High frequency Low impedance CD286
● Load life of 2000 hours at 105℃
● High frequency，Low impedance
● High performance and reliability
● For switching mode power supplies (SMPS) and industry electronics
Dissipation Factor（Tan δ ）：8%~22%
Load Life (105℃)
Leakage Current：Not more than the specified value.
Capacitance Change：Within±20% of the initial value
Dissipation Factor：Not more than 200% of the specified value
Shelf Life (105℃)
1000hours. No voltage applied. After test: UR to be applied for 30 minutes, 24 to 48 hours before measurement.
Convert alternating current into direct current (dc), for the smooth after the rectifier dc, often need capacitor filter, and the peak will be from zero to 1.414 times (RMS) smooth as close to a smooth dc voltage to a large electric capacity of capacitor, and require small size, price cheap, this is electrolytic capacitor.
Aluminum electrolytic capacitor (also called electrolytic capacitor) is how to achieve high electric capacity? First of all, to increase the plate area effectively, increase the plate in the electrolytic capacitor effective area method is that its anode aluminum foil corrosion is very rough, corrosion foil or tantalum metal powder caking structure to increase the surface area as possible, but only by increasing the positive surface area of the rough and metal anode in fact does not increase the plate effective area, only the cathode substrate as rough as the anode and the surface of the two electrodes is closely to realize effective increase of plate area, which in fact is not possible.
To realize the positive and negative electrodes in close contact under rough surface is only one electrode is solid metal, and the other electrode is solid or trying to create such a negative, such as conductive liquid or gas, gas is much less than the conductivity of liquid, so the electrode should be conductive liquid, so two electrode area can is much bigger than the electrode geometry size, electric capacity greatly increased.Then the problem is medium, what kind of medium can change with coarse metal electrodes arbitrarily?Obviously, in the form of insert film dielectric is certainly not.
There is a certain type of metal is called valve metal, this kind of metal can be obtained by anodic oxidation method has good oxidation film used to form a capacitor dielectric insulation, this kind of metal aluminum, tantalum, niobium and titanium.In this way, can use aluminum or tantalum anode oxidation method and the oxide film formed in the surface features, using alumina, tantalum oxide film dielectric, because the alumina, tantalum oxide has high dielectric strength and relative dielectric coefficient of large [relative dielectric coefficient for alumina for 8, tantalum oxide for 20 or so, far higher than that of general thin film dielectric coefficient (2 ~ 3)], as a result, aluminum electrolytic capacitors, tantalum electrolytic capacitor of capacitance can be general capacitor hundreds of times, it is easy to get hundreds or even thousands of micro method, capacitance is that this is generally film capacitor.
Basic knowledge of the electrolytic capacitor
Usually by anode aluminum foil, aluminum electrolytic capacitor cathode foil overlap after winding shaping and isolation of paper, then soak liquid electrolyte, and the end line (or bolt) installed in the container.The anode aluminum foil is high purity aluminum erosion in thousands of tiny tunnel, in order to increase the contact area and the electrolyte, the microstructure of anodic aluminum foil after corrosion process.
Positive plate of aluminum electrolytic capacitor anodic foil, dielectric in anode foil on the insulation of the alumina, the real negative plate is conductible liquid electrolyte, cathode foil for real negative electrode derivation of the electrolyte.Because after corrosion process of anode aluminum foil surface area of the hundreds of times as much land as is its geometry, and aluminum oxide dielectric is less than the thickness of micron.So the capacitor has a huge board area and very close to the plate distance, therefore, can get very large capacitance.Electric capacity can reach 2 000/6.3 000/6.3 7000 V (CDE) and 10 V (JINPEI brand LOW ESR electrolytic capacitor), is close to 3 f rated voltage can be overridden from 3 V LOW voltage to high voltage of 500 V is the voltage range.
Through described above may know, usually the capacitor has obvious positive and negative side, there is a polar components, not reverse polarity.
The production process
The production process of aluminum electrolytic capacitors are mainly the following several steps.
Yang, the cathode is composed of very pure and thin aluminum foil, aluminum foil thickness 0.02 ~ 0.1 mm.In order to increase the capacitance and size of the panel, can foil by corrosion method to form a very rough surface to increase the surface area, and through the electrolyte with very rough surface contact closely.
(2) by anodic oxidation form anodic film
Aluminum electrolytic capacitor medium on the anode foil.The medium is the thin layer of alumina Al2O3, in known as "anodic oxidation in the process of formation on the anode foil by electrochemical method.Its technological process is: the anode foil on the aluminum foil roll through the electrolyte slot, continuous application slot and foil the DC voltage complete formation process.Voltage is the ultimate capacitor voltage rating of 135% ~ 200%, therefore, the medium thickness of the aluminum electrolytic capacitors can be precisely controlled.Usually the thickness of the aluminum oxide about every v formation is 1.4 ~ 1.5 mm, such as 450 v voltage capacitor anode foil forming can be greater than 600 v, the oxide thickness is 900 nm 1/100 of the diameter of less than a human hair.
Because of microscopic parts may be alumina block, anodic oxidation anode foil reduces the effective surface area.Can also through the special corrosion model through the choice of foil and etching process adjustment, in order to make full use of the low positive microstructure.Cathode foil without anodic oxidation, in order to maintain its large surface area and the electrolyte of electric contact.
40 ~ 50 cm wide after corrosion and anodic oxide aluminum foil volume, according to the length of the condenser is divided into many width.
(4) the riveting, winding
Anode foil, lead wire of the cathode foil riveting or welding on the anode foil, the cathode foil.And anode foil, the cathode foil and white to the isolation between paper and by winding machine winding into capacitor core package (element), the last good shape with adhesive plaster.
Synthetic electrolyte capacitor core soaking in saturated paper isolation layer and in all the parts of the corrosion of aluminum foil.The penetration method need to expel gas in core package, therefore, the core package needs to vacuum soaking electrolyte.
Electrolyte is easy to evaporate at high temperatures, so as to reduce the effective area of the cathode, thus, electrolytic capacitor need to seal.S in the 1960 s or earlier, in order to reduce costs and reduce the dosage of aluminum (aluminum production is not high at the time, and aluminum is mainly used to do the plane at that time) in our country, many commercial grade electrolytic capacitor (then called the military-to-civilian) using wax paper barrels, both ends with resin potting, because of the sealing is poor, in use for several years more failure (sometimes only one or two years to complete failure, such as the vacuum tube radio of steamboat, harmful coupling caused by high power ac impedance of self-excited phenomenon - is the electrolyte in electrolytic capacitor volatile left after the lack of electricity capacity, and serious hum told filter thoroughly with electrolytic capacitor failure), and the working temperature is + 55 ℃.Now the electrolytic capacitor core is sealed in a container.Most of the container is aluminium, the container port with good sealing rubber plug or rubber mat and resin plate and compression (as shown in figure 4.4), in order to effectively prevent the volatilization of the electrolyte.To prevent electrolytic capacitor in the gas pressure caused by the failure of the explosion, more than 8 mm diameter of the electrolytic capacitor are installed pressure relief devices, usually in aluminum shell on the end face engraved with K, >, and x type indentation, make the air pressure inside the electrolytic capacitor does rose glue before rupture pressure.
Electrolytic capacitor made the last step is aging, also known as fu, its role is to the manufacturing process (especially the anode aluminum foil cutting process) in the medium of alumina membrane damage by applying forward voltage) anodic oxidation (similar to the way of repair, as much as possible to reduce the defects of electrolytic capacitor.Applying the dc voltage is greater than the rated voltage on the capacitor voltage but less than the original anodic oxidation of aluminum foil process.Usually applied voltage on the capacitor rated temperature, but other temperature even at room temperature may also be applied.By aging, can repair the electrolytic capacitor and alumina medium damage due to the chloride ion erosion of alumina medium for electrolytic capacitor after aging performance (mainly the leakage) is still not deemed to be unqualified shall be as indicators of take out from the product, this can effectively reduce or eliminate early failure (the factory damage).Of course, leakage current indicator is a sign of aging to complete.
For users, but also know the voltage, capacitance, leakage current, parasitic parameters, ripple current and fever, and life.Below will be detailed research problems that should pay attention to these parameters and applications.
(7) Aluminum electrolytic capacitor voltage, capacitance, and leakage current
Aluminum electrolytic capacitor voltage indicators mainly include: DC rated voltage, rated surge voltage, transient overvoltage and reverse voltage, etc
(1) the rated DC voltage
VR is rated DC voltage capacitor at the rated temperature range allowed by the continuous working voltage, it includes the DC voltage between the two electrodes in capacitor voltage or continuous pulse voltage and pulse.Usually, the aluminum electrolytic capacitor rated voltage in the capacitor surface.Usually rated voltage 100 v or less as "low" aluminum electrolytic capacitor, rated voltage 150 v or higher for "high pressure" aluminum electrolytic capacitors.
(2) the working voltage
Working voltage VOP is capacitor at the rated temperature range allowed by the continuous working voltage.In the whole operating temperature range, capacitor can be either in full rated voltage (including ac superposition voltage) under continuous work, can work continuously in any voltage value between 0 v with rated voltage.In a short period of time, capacitors can also withstand - reverse voltage of 1.5 V.
the reverse voltage
Aluminum electrolytic capacitors are polar capacitor, usually are not allowed to work in reverse voltage.Where needed, can be connected through a diode to prevent reverse polarity.Usually, use the turn-on voltage of 0.8 V diode is allowed.In 1 s in short period of time, the reverse voltage is less than or equal to 1.5 V can afford, but it is only a short time, can not be continuous working condition.
(4) the surge voltage rating
Rated surge voltage VS short aluminum electrolytic capacitor is able to withstand voltage value, the test condition is: capacitor working temperature is 25 ℃, no more than 30 s, two intervals not less than 5 min.IEC 384-4 specified in the surge voltage and rated voltage of the relationship is as follows:
VR < 315 v v = 1.15 VR
VR > 315 v v = 1.10 VR
(5) the surge voltage measurements
Surge voltage rating of the capacitor VS specific test method is in the normal room temperature, electric capacity under 2500 aluminum electrolytic capacitor in series 1000 Ω plus or minus 10% resistance to limit the initial charging current, and power capacity in 2500 or higher, the value of the resistor in series basis as follows: the series resistance of the resistance value and the measured electric capacity of capacitor product (time constants) is equal to 2 500 000 Ω ·, such as the capacitor being measured for 10, 000, the series resistance of 250 Ω, and so on.In voltage 30 s through 270 s off cycle, each capacitor discharge by charging resistance or equivalent resistance.Repeat 120 h cycle.Through test requirement is that dc leakage current (DCL) before and after the test, the ESR and loss factor (DF) there should be no change of the value, and there is no mechanical damage or electrolyte leakage.Through the test conditions as you can see, the aluminum electrolytic capacitor and the series resistance of the time constant is 2.5 s, 30 s is 12 time constant, this long on time can make the aluminum electrolytic capacitor charging to the surge voltage value.120 h hit 1440 times.If the quality closes nevertheless, impact certainly will fail after so many times.
(3) (6) instantaneous overvoltage
Aluminum electrolytic capacitor can instantly under the limit of the overvoltage in general.More than 50 v is greater than the capacitor over voltage surge voltage ratings application can result in large leakage current and constant voltage state, much like the reverse characteristics of zener diode.If can't bear the instantaneous overvoltage, electrolysis capacitor may fail, but if you can afford, this state will not for too long, because the hydrogen produced by the pressure caused by the capacitor can lead to irreversible pressure relief device, disable aluminum electrolytic capacitor.In special applications (such as lightning impulse voltage) need to tolerance, to the use of special design, such as on both ends of aluminum electrolytic capacitors in parallel transient voltage suppression diode clamping or excellent performance of varistor can successfully implement instantaneous overvoltage protection.
(7) ac overlay, ripple voltage
Between aluminum electrolytic capacitor terminals can not only exert a dc voltage, and can also be applied ac superposition voltage or ripple voltage, but must meet the following conditions (1) superposition of dc voltage and ac voltage and ripple voltage is less than the sum of the rated voltage, and not reverse polarity occur;(2) the electric current shall not exceed the rated ripple current.
Electrolytic capacitor rated voltage VR, surge voltage VS, anodic oxidation voltage breakdown voltage (VF), the relationship between leakage current,
Leakage current increases with rising voltage of the electrolytic capacitor, when the voltage across more than rated voltage and approaching surge voltage, leakage current rise rate increases with the rise of voltage, when the terminal voltage close to breakdown voltage leakage current will increase sharply, finally become a similar constant pressure characteristics of avalanche breakdown.Can use of aluminum electrolytic capacitor leakage current in the voltage of the capacitor close to the characteristics of surge voltage increased significantly after measurement of aluminum electrolytic capacitor is rated voltage.
Aluminum electrolytic capacitor of capacitance indicators mainly include: the rated capacitance, electrostatic capacitance, the temperature characteristic of capacitance, the frequency characteristics of capacitance and the capacitance tolerance range, etc.
(1) rated capacity
The rated capacitance is nominal capacitance, defined in 120 hz and 25 ℃.Rated capacity is the single capacitance.The nominal capacitance of majority for the E3 series capacitance preferred value, namely: 1.0, 2.2, 3.3, 2.2, 3.3.A few also have with the E6 series preferred value, namely: 1.0, 1.5, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 4.7.
Electrostatic capacitance, dc capacity that is measuring the charge in the dc voltage applied to a capacitor, capacity at room temperature slightly bigger than the communication, and has a superior stability characteristic.
(2) the capacitance measurement
Capacitance of a capacitor by testing its ac impedance or test it can keep the battery under dc voltage is obtained.The result of two methods is slightly different.In general, the dc voltage test method measured the capacitance value of capacity (dc) to slightly higher than that of alternating current method measured capacitance (alternating current capacity).
In order to the most common applications (such as rectifier filter or direct coupling conditions are consistent, alternating current (ac) capacity of aluminum electrolytic capacitor is the most common test frequency is 50 hz or 60 hz commonly 2 times the frequency of alternating current (ac)., IEC384 IEC384-1-4 shows the frequency of 100 hz and 120 hz is in and IEC384 IEC384-1-4 of special test method is presented.
In aluminum electrolytic capacitor impose a less than or equal to 0.5 V (doesn't make the aluminum electrolytic capacitor reverse breakdown) of ac voltage detector, according to the capacitive reactance under fixed frequency capacitance current and the relationship between the capacitance and capacitive reactance and the relationship between voltage and current C = I/(2 V) can be determined.Alternating current capacity may be greater than 10%, along with the change of temperature and decreases with increased frequency, therefore, and IEC384 IEC384-1-4 shows the frequency of 100 hz and 120 hz, when the temperature is 20 ℃, the basic test conditions.Can also be used to test the general capacitor of capacitance test method, using the test using capacitance bridge type circuit, the power supply side exert maximum 1 vrm3ac signal voltage of the AC signal is no dc component and high harmonic voltage and harmonic 120 hz sine wave voltage, while the power supply voltage peak close to 1.5 V, but through the role of the partial pressure bridge type circuit, to the peak of the aluminum electrolytic capacitor voltage will be lower than 1 V, aluminum electrolytic capacitor will not cause damage.In general, after more than aluminum electrolytic capacitor used in rectifier filter and direct coupling, the capacitance value and the accuracy is not high, its capacitance tolerance (accuracy) is a plus or minus 20% can well meet the requirements.
In some applications, such as discharge circuit and timing circuits, dc capacitor will be decisive role.This would require the measurement of capacitor, it is usually possible to adopt the way of charge/discharge, according to the capacitance and electric charge, the relationship between the voltage and the relationship between the charge and current, with constant current charge/discharge way [= C (I, t)/delta VC], by detecting the t to get the capacitance C.Therefore, when in need of precise dc capacity best without aluminum electrolytic capacitor, which USES is to adopt large and small capacitors in parallel to get more precise capacitance.
(3) the capacitance temperature characteristic
Capacitance change with temperature.Change itself is determined by the rated voltage and capacitor size.Capacitance in high temperature 25 ℃ to limit increased less than 10%, the lowest rated temperature of 40 ℃, a 20% drop in low voltage electric capacity of capacitor is a typical high pressure electric capacity of capacitor dropped to 40%.Most of in - 40 ℃ drop less than 10%, in - 55 ℃ less than 20%.Different rated voltage of the electric capacity of aluminum electrolytic capacitor with temperature as shown in figure 4.6.Can see by the picture, normally, when low rated voltage characteristic curve is steep, and this is usually in order to increase the anode surface area and corrosion more coarse corrosion (depth)., of course, can also be applied special electrolyte (electrolyte viscosity with temperature changes smaller) to obtain the smaller capacitance change with temperature, able to work under 0 ℃ large capacitors within the scope of the electric capacity change is not big, it is meaningful in special applications.
(4) the relation between capacitance and frequency
Effective capacitance decline with the increase of frequency.A widespread view is that this is caused by dielectric absorption and loss factor, the concept in the dielectric loss as the major loss of film capacitor is undoubtedly correct, but the loss in the aluminum electrolytic capacitor as the electrolyte resistance of electrode produce loss, the frequency characteristics of alumina is never so bad!So the aluminum electrolytic capacitor of capacitance decreases with the rise of frequency characteristics should not be the problem of dielectric loss, so what's the problem?The author's view is that: because of the aluminum electrolytic capacitor to increase the surface area and the anode/cathode foil corrosion is very rough, so, with the deep rough anode electrode corresponding is the cathode electrolyte.Because electrolyte with high resistivity and rough deep anode electrode capacitance to the terminal, in fact, has become a RC circuit, as frequency increases, the son of capacitance effect is more and more weak, the equivalent capacitance is becoming more and more small, this is the aluminum electrolytic capacitor of capacitance decreases with increased frequency, the real reason for aluminium electrolytic capacitor similar equivalent circuit will be detailed research and analysis in section 4.7.
(5) the capacitance tolerance
Capacitance tolerance is to allow the minimum or maximum differential capacitance and the rated capacitance value with the ratio of the rated capacitance, usually expressed as a percentage (delta C/C).Typical capacitance tolerance + / - 20% and - 10% + 50% and - 10% + 75%.High voltage capacitor tolerance can be made smaller, such as greater than the general tolerance can be less than 150 v + 10%.Capacitance change with temperature and frequency, usually the change should be within the scope of the capacitance tolerance.Usually this change itself is also affected by the rated voltage of capacitor and capacitor size.
Due to tarticularity of medium which ACTS as an insulating layer of the alumina, alumina medium corrosion caused by chloride ions in the electrolyte defects caused by leakage current, dc voltage needed by applying the patch (anodic oxidation), as a result, even if has applied dc voltage for a long time, there will be a small repair currents, the current is called leakage current.Low leakage current means that the chloride ions in the electrolyte, can get good repair as a result, also shows that as insulation medium of alumina is good.The iron, copper ions in the electrolyte on the aluminum electrolytic capacitor electrode voltage after current will generate galvanic effect, need more charge to consume it, this is some of the aluminum electrolytic capacitor after power up "leakage" for a long time is needed to drop to normal.
(1) leakage current measurement method
Aluminum electrolytic capacitor leakage current test method and test conditions for: at 25 ℃, measured the protection of the capacitor in series a 1000 Ω resistance to the rated voltage, leakage current measurement.Applied voltage after 5 min, the maximum leakage current shall not exceed the specifications for qualified.Small capacity of aluminum electrolytic capacitor can be used in a 1 min test results, the large capacity of aluminum electrolytic capacitor will need longer time to test.
It is important to note that the aluminum electrolytic vessel after long time no voltage state of storage without any application of the chloride ions in the electrolyte damage in alumina films were the biggest, especially under the condition of high temperature storage, in this case from the oxide layer to the anode without leakage current through the, oxide layer will not be able to produce again.Result is that after the extension of the storage access voltage, leakage current will produce a higher than normal.However, as the oxide layer to produce in the course of using, the leakage flow gradually decreased to normal.At the same time, the galvanic effect of iron, copper ion gradually restored, the aluminum electrolytic capacitor leakage current will need a long time of the applied voltage to restore them.This process is called aging or known as fu can.Usually in the aluminum electrolytic capacitor can assign the best before use.
DC leakage current is application of the rated voltage, DC current through the capacitor.Leakage current value and applied voltage, charging time, capacitance temperature.
In the condition of no voltage, domestic manufacturer of aluminum electrolytic capacitors can be stored at least 1 year, foreign famous manufacturer of aluminum electrolytic capacitors can be stored at least 2 years.Good seal of aluminum electrolytic capacitor can store even 15 years without any performance loss.If there is no beyond aluminum electrolytic capacitor storage time, capacitor after out of the library can be directly applied to the rated voltage.In this case, can not to process.
When circuit design application, must pay attention to is the first time electricity leakage current value could be up to 100 times its normal!When the capacitor stored for more than 2 years, can withstand the high initial capacitor leakage current is very terrible.In front of the aluminum electrolytic capacitor load circuit, therefore, it is best to aluminum electrolytic capacitor can assign of the implementation process.In addition, with the capacitor circuit has reached or exceed the storage life of the above, should work in no-load state 1 h the capacitor, this will make the capacitor restoration.Thus can see, with aluminium electrolytic capacitor circuit during storage, should add electricity for several hours every year to ensure that the circuit when the continue to storage performance of the aluminum electrolytic capacitor.
(2) the temperature characteristics of leakage current
In 85 ℃ temperature range of capacitor, for example, aluminum electrolytic capacitor leakage current increased with temperature rise.
Aluminum electrolytic capacitor application regardless of whether the best charging can assign the regularly, in order to ensure the performance of the aluminum electrolytic capacitor;Aluminum electrolytic capacitor both in storage and work is not suitable for high temperature environment, high temperature environment will greatly shorten the service life of aluminum electrolytic capacitor and aluminum electrolytic capacitor leakage current performance degradation.
Parasitic parameters on the electrical characteristics of aluminum electrolytic capacitors
The special structure of aluminum electrolytic capacitors, aluminum electrolytic capacitor of parasitic parameters on the electrical characteristics of influence is very big, need careful study of aluminum electrolytic capacitor parasitic parameters and its influence on the electrical characteristics.Parasitic parameters of aluminium electrolytic capacitor mainly include: the ESR one-way insulation, parasitic inductance and anodic films, etc.On the influence of electric parameters is mainly: the frequency characteristic, the influence of temperature on the ESR and impedance frequency characteristic, the influence of temperature and frequency on the loss factor and the influence of dielectric absorption and the residual voltage and so on.
The equivalent circuit
Electrolytic capacitor under different working conditions can be expressed in different equivalent circuit, the resistance of the electrolyte, oxide film medium (was) after injury of the manufacturing process of anode foil insulation resistance, capacitance, cathode foil capacitance, the electrodes and the pins of inductor, shows that anodic oxide film is a nonpolar diodes.Electrolytic capacitor, therefore, the reverse voltage is greater than 1.5 V will cause large leakage current, much like the zener diode avalanche breakdown.In this case the electrolytic effect can produce hydrogen gas, make the internal pressure and rise pressure
relief device, at the same time, reverse voltage, will also destroy anodic films made of electrolytic capacitor pressure fell sharply.At this time of the electrolytic capacitor will fail.This is the reason why electrolytic capacitor can not reverse polarity application.Aluminum electrolytic capacitor of parasitic parameters on a large impact on the performance of the aluminum electrolytic capacitor.
Electrolytic capacitor's ESR
The ESR of the electrolyte is a key part of the aluminum electrolytic capacitor equivalent series resistance.LOW equivalent series resistance of LOW ESR aluminium electrolytic capacitor is actually picked LOW ESR electrolyte, and, most of the electrolyte resistivity decreases with temperature rise, therefore, LOW ESR aluminium electrolytic capacitor equivalent series also decreases with temperature rise.Such as a 100 (including F / 63 v and 47 (including F / 350 vlow ESR impedance frequency characteristic and the temperature of the aluminum electrolytic capacitor, the relationship between each low of a curve can be regarded as the ESR value, the ESR is close to 1.5 Ω when to 40 ℃, 25 ℃ to 0.5 today Ω, 0 ℃ to 0.1 Ω today, when the room temperature + 25 ℃ is 0.05 Ω, at + 85 ℃ under the highest working temperature of the ESR, lowest 0.04 Ω.You can see, the ESR from 25 ℃ to high temperature limit by 35% ~ 50%, but increase the low temperature limit is about 10 times.Device ESR than rated - 20 ℃ and 40 ℃ about 100 times.
For LOW ESR aluminium electrolytic capacitor, the ESR in 25 ℃ environment with valid 1 v ac signal voltage and largest 120 hz power supply without dc bias voltage of equivalent series resistance measurement circuit.
In general, LOW ESR aluminium electrolytic capacitor ESR almost small change with the increase of frequency.Range from large bolt terminals of capacitor Ω 0.002 to 10 Ω small capacitor.
The impedance frequency characteristics
Aluminum electrolytic capacitor equivalent RLC series circuit, so is lower than the resonant frequency impedance is given priority to with capacitive reactance of capacitor, the frequency characteristics of aluminum electrolytic capacitor with poor can only maintain the frequency to 20 kHZ, high performance aluminum electrolytic capacitor can be at or above 100 kHZ.Decreased with the increase of frequency, capacitive reactance, inductive, capacitive reactance is equal to the inductance and cancel each other out of the frequency of aluminum electrolytic capacitor wipe vibration frequency, the impedance of the lowest at this moment, only the ESR.If the ESR zero, then the impedance of the zero;Frequency continues to rise, inductance start is greater than the capacitive reactance, when impedance close to the ESR, impedance frequency characteristic started to rise, the perceptual, since the frequency above the frequency of the capacitor is actually a inductance!Because of manufacturing process, the greater the capacitance and parasitic inductance is, the greater the resonance frequency and the lower the increase of capacitance (actually itself, leading to low resonant frequency), the lower the frequency of the capacitor is perceptual also.This is some literature in terms of filtering and some people often have a "big capacitor filter low frequency, small capacitance filter high frequency" statement comes in.
(2) the electrolytic capacitor ESR measurement
Aluminum electrolytic capacitor, the ESR is at 25 ℃, the effective value of 10 hz ~ 100 KHZ tunable 1 v ac signal voltage of the inverter power supply measurement test under the bridge.The impedance measurement is typical characteristic curve and the low temperature limit of measurement.
To measure impedance at low temperature, put the capacitor in indoor, set plus or minus 2 ℃ low temperature.In (120 + 5) HZ frequency application of any can provide the right method to measure the impedance plus or minus 2.5% accuracy.Temperature stability, should be as low as possible as soon as possible of the AC voltage measurement, so that it will not cause the capacitor fever.
By displaying in two consecutive measurements within 15 min interval does not change, assumes that the capacitor to achieve thermal stability.
(3) the temperature characteristic of electrolytic capacitor
Capacitive impedance temperature characteristic of aluminum electrolytic capacitor and due to the temperature of the impedance characteristics of parasitic inductance and basically does not change with temperature, resistance temperature characteristic is plays a main role in the ESR varies with temperature change is big, this is decided by the electrolyte temperature characteristics of the resistivity of the.
(4) the inductance
Equivalent series inductance, inductance is relatively independent of the frequency and temperature.Typical value range of surface mount (SMT) 2 ~ 8 nh radial lead 10 ~ 30 nh and axial lead 20 nh.The inductance value changing with lead to electrode position number and way.
(5) resonance frequency
Resonance frequency is capacitive reactance 1 / () and impedance 1 / () equal frequency.This is because the capacitive reactance and impedance phase difference of 180 °, the two reactance destructively, only impedance is purely resistive, and in the frequency of the ESR is equal.After above the resonant frequency impedance sensibility.Typical values of aluminum electrolytic capacitor, resonance frequency should be a lot more than 120 hz capacitor of the rectifier filter frequency, the resonance frequency of the aluminum electrolytic capacitor now generally in more than 20 KHZ, used for high frequency filter can reach more than 100 KHZ resonance frequency.
The loss factor
Under alternating current excitation, according to the original definition of capacitor loss factor, obviously, this is the ratio of the capacitive reactance and the equivalent series resistance.This ratio is very like a trigonometric function on the side near the side - tangent function.Therefore, the loss factor of electrolytic capacitor (DF), also known as a lot of technical literature loss tangent.
Increase with the increase of frequency (that is), the CR increases, the loss factor of the aluminum electrolytic capacitor with the increase of measuring frequency and bigger.
The ESR with temperature rising and falling, suggesting that the loss factor of aluminum electrolytic capacitor will bear decreases with the rise of temperature, therefore, caused by the loss factor of loss caused by temperature rise, be suppressed.This is the result of a convergence.Electrolyte resistivity decreases with temperature rise, therefore, the loss factor with temperature drop (ESR).The loss factor of temperature characteristic and frequency characteristic.
It is important to note that the aluminum electrolytic capacitor loss characteristics is not the medium of aluminum electrolytic capacitor dielectric loss (alumina), but as the cathode due to the resistance of the electrolyte, the non-polar capacitor due to the loss of the dielectric loss factor has a qualitative difference.
Because of the loss factor of capacitor test standard is the use of the national first of 60 hz frequency, therefore, capacitor loss factor testing frequency is 60 hz ac full wave or the minimum ripple frequency after the bridge rectifier (double frequency of 60 hz) 120 hz.The test values are in this test conditions than frequency 50 hz power grid in our country under the loss factor of 20%.
(1) the DF measurements
DF measurement at 25 ℃, 120 hz, no positive bias voltage, maximum ac RMS 1 v signal voltage tuning conditions.DF values determined by the temperature and frequency.
(2) the dielectric absorption and residual voltage
Dielectric absorption is thought to be on both ends of the capacitor was short circuit for a period of time, then after a short circuit will be moved to, stable voltage of capacitor gradually increases and eventually in a numerical phenomenon.Usually this kind of phenomenon can be a residual voltage.This feature in the use of the harmful influence mainly is two aspects that affect the circuit parameters and dangerous for the safety of RC timing circuit, trigger system and mobile network is an important phase.In aluminum electrolytic capacitor dielectric absorption "residual voltage in the temperature of 25 ℃ environment may meet during 100 ~ 1000 s before discharge voltage value of 10%, in a temperature under high temperature, the residual voltage will be higher.For high voltage aluminum electrolytic capacitor voltage may participate in 40 ~ 50 v or higher.This will cause accidental discharge, especially of the electric shock may occur and surprises.
Biggest dielectric absorption of residual voltage can pass under the rated voltage charging 1 h, through a 1 min short circuit discharge, then let stand open after a period of time in the high impedance were measured potentiometer.
Another explanation is that the residual voltage: due to the aluminum electrolytic capacitor to increase the surface area and the anode/cathode foil corrosion is very rough, so, with deep rough anode electrode corresponding is the cathode electrolyte.Due to the electrolyte with high resistivity makes rough deep anode electrode capacitance to the terminal, in fact, has become a RC circuit, a short short circuit could not rough anode electrode depth charge after the parasitic resistance full discharge and quite a number of remaining charge, when the internal short circuit after remove the aluminum electrolytic capacitor charge will be rebalanced, the final balance as a result, to participate in the voltage value.Dielectric absorption and parasitic resistance which are even more important in the process of the output voltage is to participate in, the authors think that the role of parasitic resistance in the aluminum electrolytic capacitor is bigger, because in college physics when it comes to the turning of the dielectric polarization relaxed time is very short, even with medium polarity to the polarization relaxed time also was only about 10-5 ~ 10-3 s , it is hard to imagine 100 ~ 1000 s time.
Aluminum electrolytic capacitor discharge shall, by means of resistance and unfavorable use direct short circuit for high voltage large capacity aluminum electrolytic capacitor should discharge resistor in parallel, in order to avoid participating in the generation of voltage.
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