Capacitor is the most widely used, the largest amount, and irreplaceable electronic components, its output accounts for about 40% of the electronic components, and aluminum electrolytic capacitors and three categories of capacitors (electrolytic capacitors, ceramic capacitors, organic film capacitors) accounted for 36.8% of the output.Electrolytic capacitor is one of the components with the fastest development speed in China in the past 10 years. At present, the annual production volume of domestic electrolytic capacitor is close to 25 billion, with an average annual growth rate of up to 28%, accounting for 1/3 of the global output of electrolytic capacitor.In the development process, aluminum electrolytic capacitors also have from integrated circuits, complete circuit improvements and in high voltage, high frequency, long life, small capacity applications in other capacitors (such as multilayer single-stone ceramic capacitors, metallized film capacitors, tantalum electrolytic capacitors, etc.) mutual penetration.Aluminum electrolytic capacitor itself is constantly improving, perfecting and innovating.Especially with the development of science and technology, the improvement of social demand, the improvement of the environment, the birth of new complete machine, make miniaturization, chip and medium high voltage large capacity aluminum electrolytic capacitor application field is constantly expanding, the demand is increasing.Therefore, aluminum electrolytic capacitor not only will not shrink, but also has a stronger vitality and broader development space, will have a faster growth rate.
Aluminum electrolytic capacitor is made of anode aluminum foil after corrosion and oxidation film formation, cathode aluminum foil after corrosion, between the electrolytic paper winding, then impregnated with working electrolyte, and then sealed in the aluminum case.Its performance characteristics are described below.
1.1 The electric capacity per unit volume is very large
The capacitance of a capacitor C= 0 rS/d, where 0 is the vacuum capacitance (constant), r is the relative dielectric constant of the dielectric material, S is the effective area of the electrode, and D is the thickness of the dielectric material.For aluminum electrolytic capacitors, r=8 ~ 10.Anodic and cathodic aluminum foils can be corroded to increase their surface areas by tens to hundreds of times.D = Vf, ≈1.4nm/V, Vf=10V ~ 600V, then D is about 0.014 m ~ 0.9 m, several times to several hundred times smaller than other capacitors.As a result, the capacity per unit volume of electrolytic capacitors is several times to dozens of times larger than other capacitors.
1.2 Very large rated capacity Due to the winding structure of the electrolytic capacitor, it is easy to expand the volume, so it can easily achieve the rated capacity of tens of thousands of micromethods or even hundreds of thousands of micromethods.
1.3 have self-healing effect due to internal have electrolyte capacitor, therefore, in the work, the capacitor anode aluminum foil on the dielectric in the event of local failure, O2 - OH - or in the electrolyte of acid radical ion in the electric field force, rapidly reach the damage position, will damage location obstructed, and will break the oxide film repair, capacitor returned to normal state.
1.4 High working electric field Strength Since the anodic oxidation film grows at about 1.4nm per volt during the formation process, that is, the electric field strength when the anodic oxidation film grows is about 7×107V/cm, and its working electric field strength is about 5×107V/cm, which is far greater than the working electric field strength of ceramic capacitors and film capacitors.
As the main raw materials used in manufacturing aluminum electrolytic capacitors are ordinary industrial materials, the equipment used belongs to general industrial equipment and has a high degree of automation, so the manufacturing cost is relatively low, especially the manufacturing cost per unit capacity has an overwhelming advantage over other types of capacitors.
2. Disadvantages of aluminum electrolytic capacitor
Due to the polarity of the electrolytic capacitor, it is necessary to pay attention to the correct connection of the positive and negative poles in use, otherwise the capacitor will not play its role, and the leakage current is very large, which will heat up inside the capacitor in a short time, destroy the oxide film, and then be damaged.Aluminum electrolytic capacitors are sealed with an aluminum case and rubber plug. When the working electrolyte vaporizes under heat, it is easy to leak out from the root of the lead.The electrolyte dries up and the capacitor becomes ineffective after a long period of operation.This is one of the main failure modes of aluminum electrolytic capacitors.
2.2 Large tangential value of loss Angle and relatively poor temperature and frequency characteristics Working electrolyte plays the role of cathode in aluminum electrolytic capacitor. Because working electrolyte is an ionic conductor and the movement speed of ions is much slower than that of electrons, the conductivity of working electrolyte is lower than that of electronic conductor.Therefore, the equivalent series resistance caused by working electrolyte is higher than that caused by metal electrode of other capacitors. As a result, the tangential value of loss Angle of aluminum electrolytic capacitor is larger and the frequency characteristic is relatively poor.In addition, because the conductivity of liquid material is greatly affected by temperature, so the temperature characteristics of aluminum electrolytic capacitor is relatively poor.
2.3 Although weak acid/weak base salt is used as electrolyte and water and organic solvent as solvent, the aging working electrolyte is still corrosive to a certain extent, and has a certain erosion effect on the anodic oxidation film and rubber plug of the capacitor.In addition, certain chemical reactions will occur between electrolyte salts and solvents over time.These phenomena will lead to the electrical properties of capacitors.In short, although aluminum electrolytic capacitor has certain disadvantages, which limit its application in some occasions, due to its significant advantages such as high capacity and price advantage, it firmly occupies more than 30% of the shares in the competition with ceramic capacitors, film capacitors, and tantalum electrolytic capacitors.And with the development of automobile electronics, frequency conversion technology and other power electronics technology, its proportion will increase greatly.
3 the vitality of aluminum electrolytic capacitor with the development of science and technology, especially the integrated circuit (IC) and the development of very large scale integrated circuit (VLSI), the capacitor industry sustainable development, and even no living space has been doubted, however, since 1987, the global production of capacitor is growing at more than 20% a year, to dispel the doubt.Practice has proved that aluminum electrolytic capacitor has extremely strong vitality.
3.1 The development of IC cannot replace the aluminum electrolytic capacitor. On the one hand, due to the appearance of IC, some small capacity capacitors are integrated into the circuit.On the other hand, with the development of IC, the working frequency of the circuit system is greatly increased, leading to the replacement of aluminum electrolytic capacitors in some circuits by other capacitors.However, the power supply part of IC circuit is always inseparable from the electrolytic capacitor.In addition, the improvement of the performance of aluminum electrolytic capacitors extends to other capacitor applications.
3.2 the whole machine circuit changes only changed the model of aluminum electrolytic capacitor of switch power supply volume shrinking, increasing efficiency of energy conversion, make increasing the working frequency of switch power supply (from 20 KHZ to 500 KHZ, even achieve more than 1 MHZ), causes the output section of high frequency noise, in order to effectively filter, you must use the ultra high frequency impedance and low equivalent series resistance (ESR) capacitor.
