Low ESR aluminum electrolytic capacitor

Electrolytic Capacitors High frequency Low impedance CD286

FEATURES ● Load life of 2000 hours at 105℃ ● High frequency，Low impedance ● High performance and reliability ● For switching mode power supplies (SMPS) and industry electronics

SPECIFICATIONS

Rated Voltage：DC6.3~100V

Capacitance：12μF~15000μF

Capacitance Tolerance：±20%

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.
(1) corrosion
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.

(3) cutting
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.
 
(5) soaked
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.
 
(6) seal
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.

(7)aging
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
 
voltage
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.

capacitance
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 alumin