Type of electrolytic capacitor, analysis of characteristic structure of electrolytic capacitor

Capacitors are one of the most basic electronic components in life. How much do you know about electrolytic capacitors?Do you know how electrolytic capacitors are classified?This article will reveal the classification and structural characteristics of electrolytic capacitors.

capacitor

An electronic element consisting of two conductors and an insulator between them.Capacitor as one of the three basic components, the main role is to store energy and filter, in addition to direct, bypass, coupling, rectification, tuning, energy conversion and other functions;According to statistics, the fault caused by capacitor selection and application accounts for about 55 ~ 85% of the total failure efficiency of the capacitor.The failure of capacitors due to their own mass accounts for about 15 ~ 45%.Therefore, the choice and application of capacitors in electronic products is the basis of ensuring product quality and reliability.

Main characteristic parameters of capacitor

Main characteristic parameters of capacitor

(1) nominal capacitance

The capacitance of a capacitor.However, there is a deviation between the actual capacitance and the nominal capacitance.General capacitor common Ⅰ, Ⅱ, Ⅲ level, electrolytic capacitor with Ⅳ, Ⅴ, Ⅵ level, according to the purpose.The capacitance of an electrolytic capacitor depends on the impedance present when the capacitor is operated at ac voltage. The capacitance will vary with the operating frequency, temperature, voltage and measurement method.

Rated voltage

The RMS value of the highest dc voltage that can be continuously added to the capacitor at the lowest ambient temperature and rated ambient temperature. If the working voltage exceeds the capacitor's withstand voltage, the capacitor will be broken down, causing damage.In practice, as the temperature increases, the pressure will decrease.

Insulation resistance

The ratio of a dc voltage to a leakage current applied to a capacitor is called insulation resistance.When the capacitance is small, it mainly depends on the surface state of the capacitance.Capacity >0.1 F depends largely on the medium.The greater the insulation resistance, the better.

(4) loss

Under the action of electric field, the energy consumed by the capacitor due to heat in unit time is called loss.The loss is related to the frequency range, the medium, the conductance, the resistance of the capacitance metal part, etc.

(5) frequency characteristic

With the increase of frequency, the capacitance of general capacitors decreases.When the capacitor works below the resonant frequency, it is capacitive; when it exceeds the resonant frequency, it is inductive. In this case, it is not a capacitor but an inductor.Therefore, it must be avoided that the capacitor works above the resonant frequency.

The capacitor chooses several parameters that are commonly used

Temperature coefficient, that is, the value of capacitance with the temperature range.

(2) loss factor, because the capacitor leakage resistance, equivalent series resistance and equivalent series inductance, these three indicators are almost always difficult to separate, so many capacitor manufacturers will combine them into a single index, called loss factor, mainly used to describe the capacitor invalid degree.The dissipation factor is defined as the ratio of the dissipated energy to the stored energy per cycle of the capacitor.Also known as loss Angle tangent.

The Q value, also known as the quality factor, is the reciprocal of the loss factor.Q or loss factor will be noted in the manual of common capacitors.(4) dielectric constant K, capacitance is the main difference between the filling medium, the size of the dielectric constant relation capacitance volume and dielectric absorption is different, the dielectric constant is large, in a small volume can be integrated with a large capacity, but the dielectric absorption is very serious.

Electrolytic capacitor

Electrolytic capacitors are usually made of metal foil (aluminum/tantalum) as the positive electrode, and the insulating oxide layer of metal foil (aluminum oxide/tantalum pentaoxide) as the dielectric.The negative electrode of an aluminum electrolytic capacitor consists of a thin paper/film or an electrolyte polymer impregnated with an electrolyte solution (liquid electrolyte);The negative electrode of tantalum electrolytic capacitor is usually manganese dioxide.Electrolytic capacitors get their name because they use electrolytes as the negative electrode (note the difference between dielectric and electrolyte).

Type of electrolytic capacitor

According to analysis and statistics, electrolytic capacitor packaging types are mainly divided into the following 10 categories:

1.According to the structure of three categories: fixed capacitors, variable capacitors and trimmer capacitors.

2.Classification by electrolyte: organic dielectric capacitor, inorganic dielectric capacitor, electrolytic capacitor, electrothermal capacitor and air dielectric capacitor.

3, according to the purposes are: high frequency bypass, low frequency bypass, filtering, tuning, high frequency coupling, low frequency coupling, small capacitor.

4.According to the different manufacturing materials can be divided into: porcelain dielectric capacitor, polyester capacitor, electrolytic capacitor, tantalum capacitor, and advanced polypropylene capacitor and so on

5.High frequency bypass: ceramic capacitor, mica capacitor, glass film capacitor, polyester capacitor, glass glaze capacitor.

6.Low-frequency bypass: paper capacitor, ceramic capacitor, aluminum electrolytic capacitor, polyester capacitor.

7. Filtering: aluminum electrolytic capacitor, paper capacitor, composite paper capacitor and liquid tantalum capacitor.

8.Tuning: ceramic capacitor, mica capacitor, glass film capacitor, polystyrene capacitor.

9.Low coupling: paper capacitor, ceramic capacitor, aluminum electrolytic capacitor, polyester capacitor, solid tantalum capacitor.

10.Small capacitors: metallized paper capacitors, ceramic capacitors, aluminum electrolytic capacitors, polystyrene capacitors, solid tantalum capacitors, glass glaze capacitors, metallized polyester capacitors, polypropylene capacitors, mica capacitors.

Analysis of characteristic structure of electrolytic capacitor

Electrolytic capacitor is a capacitor, can be divided into two types, nonpolar and polar, metal foil as the anode (aluminum or tantalum), and the positive close to metal oxide film (alumina or tantalum pentoxide) is a dielectric, the cathode by conductive material, electrolyte, electrolyte can be either liquid or solid) and other materials, because of the electrolyte is a key part of the cathode, electrolytic capacitor hence the name.At the same time, the positive and negative of the electrolytic capacitor shall not be misconnected.

I. electrolytic capacitor structure:

Aluminum electrolytic capacitor is a polar capacitor, its positive plate with aluminum foil, dip it in the electrolyte for anodizing treatment, aluminum foil surface will produce a layer of aluminum oxide film, its thickness is generally 0.02-0.03 m.The oxide film is the insulating medium between positive and negative plates.The negative electrode of the capacitor is composed of electrolyte, which is generally composed of boric acid, ammonia water and ethylene glycol.In order to facilitate the manufacture of capacitors, the electrolyte solution is usually impregnated on a special paper, and then a piece of raw aluminum and the paper soaked in electrolyte solution are bonded together, so that it can be more convenient to lead out the negative electrode in the raw aluminum foil strip.

As shown in the figure.Winding the positive and negative electrodes according to their central axes constitutes the core of an aluminum electrolytic capacitor, which is then encapsulated in an aluminum shell to form an aluminum electrolytic capacitor.In order to keep the electrolyte solution from leaking and drying, the mouth of the aluminum shell of the electrolytic capacitor package is sealed with a rubber plug.In order to obtain larger capacitance and smaller volume, the side of the positive electrode aluminum foil is chemically etched to form a convex and concave surface, which increases the surface area of the electrode and thereby increases the capacitance.The reason why aluminum electrolytic capacitor has polarity is that the alumina film on the positive electrode plate has unidirectional conductivity. Only when the positive pole of the capacitor is connected to the positive pole of the power supply and the negative pole of the power supply is connected to the negative pole can the alumina film play the role of insulating medium.If the polarity of the aluminum electrolytic capacitor is reversed, the aluminum oxide film will become a conductor. The electrolytic capacitor will not only fail to play a role, but also have a large current through, causing overheating and damage to the capacitor.In order to prevent the accidental explosion of aluminum electrolytic capacitors in use, the end face of aluminum shell package is generally used to suppress the mechanical weak link of the directional slot. Once the internal pressure of the capacitor is too high, the groove of the weak link will crack for pressure relief and explosion protection.

Although aluminum electrolytic capacitor has polarity, it can also be made into non-polar electrolytic capacitor if new method is adopted in structure and technology.

Ii. Features of electrolytic capacitor

Electrolytic capacitors feature 1: the capacitance per unit volume is very large, dozens to hundreds of times larger than other types of capacitors.

Electrolytic capacitor characteristics 2: rated capacity can be very large, can easily be tens of thousands of f or even a few f (but not with double layer capacitance ratio).

Electrolytic capacitors feature three: the price is overwhelming advantage over other types, because the components of the electrolytic capacitors are common industrial materials, such as aluminum and so on.The equipment for manufacturing electrolytic capacitors is also common industrial equipment, which can be mass produced at a relatively low cost.Common Japanese electrolytic capacitors in Nippon chemie - con (kingbox), Rubycon (ruby), represented by sets of series capacitors with LELON (set), CAPXON (CAPXON) as the representative, the port of electrolytic capacitor with SAMXON (his), KFSON (Kang Fusong) as the representative, domestic to TH (huayugroup), and Chang (huawei), Xunda (da) and so on, Europe and the United States, represented by ELEBASIC, KENDEIL, EVERALPHA.