Capacitance is one of the widely used electronic components in electronic equipment. It is widely used in separation, coupling, bypass, filtering, tuning loop, energy conversion, control circuit and so on. C capacitor, capacitor unit Fala (F), microfarad (uF) and Pifara (pF), 1F=10^6uF=10^12pF.
Method for naming capacitor type
The type of domestic capacitor is generally composed of four parts (not applicable to pressure sensitive, variable, vacuum capacitors). The names, materials, categories and numbers are represented in turn.
Part I: name, letter, capacitor with C.
The second part: the material, using the letter.
The third part: classification, the general use of digital representation, the individual with the letter said.
The fourth part: the serial number, using the digital representation.
A letter of product material: A-, B- tantalum and other non-polar polystyrene film, C-, D-, high frequency ceramic aluminum electrolysis, E- other materials of G- alloy and H- composite medium, I- glass glaze, J- metallized paper and L- polyester and other polar organic thin film, N-, O- glass film of niobium Q-, T-, V- low frequency ceramic paint, mica paper, mica paper, Z- Y-.
Two, the classification of capacitors
The structure is divided into three categories: Fixed capacitors, variable capacitors and fine tuning capacitors.
According to the classification of the electrolyte are: organic dielectric capacitors, inorganic dielectric capacitors, electrolytic capacitors and air dielectric capacitors, etc..
There are: high frequency bypass, low frequency bypass, filtering, tuning, high frequency coupling, low frequency coupling, small capacitor.
High frequency bypass: ceramic capacitors, mica capacitors, glass film capacitors, polyester capacitors, glass glaze capacitors.
The low-frequency bypass: paper capacitor, ceramic capacitor, electrolytic capacitors, polyester capacitors.
Filter: aluminum electrolytic capacitor, capacitor, composite paper capacitor, wet tantalum capacitors.
Tuning: ceramic capacitors, mica capacitors, glass film capacitors, polystyrene capacitors.
High frequency coupling: ceramic capacitors, mica capacitors, polystyrene capacitors.
Low frequency coupling: paper capacitor, ceramic capacitor, electrolytic capacitors, polyester capacitors, solid tantalum capacitors.
Small capacitance: Metallized paper capacitor, ceramic capacitor, electrolytic capacitors, polystyrene capacitors, solid tantalum capacitors, glass glaze capacitors, metallized polyester capacitors, polypropylene capacitors, mica capacitor.
Three, commonly used capacitors
1, aluminum electrolytic capacitors
Soaked with water or paste electrolyte in two aluminum foil intermediate winded thin oxide film for capacitor dielectric. Because the film has a one-way conductive properties, so the electrolytic capacitor has a polarity. Large capacity, large error tolerance ripple current capacity, the flow is not suitable for ordinary electric leakage; in the application of high frequency and low temperature, should not be used at frequencies above 25kHz low pass, signal coupling, power filter.
2, tantalum electrolytic capacitors
Tantalum sintered as cathode, temperature characteristics, frequency characteristics and use of solid manganese dioxide * electrolyte are better than ordinary electrolytic capacitors, especially small leakage current, good storage capacity, long service life, small error, small volume and unit volume can product the capacitor voltage tolerance to pulsating current the difference, if damaged easily in short circuit state high * ultra small parts.
3, thin film capacitor
The similar structure with the paper capacitor, but with polyester, polystyrene and other plastic materials made of low loss dielectric frequency characteristics, dielectric loss can not be made into a large capacity, low heat tolerance filter, integral, oscillation and timing circuit
4, ceramic capacitor
Through type or post type ceramic capacitor, an electrode which is mounting screw. The lead inductance is small, the frequency characteristic is good, the dielectric loss is small, and the temperature compensation effect can not be made into a large capacity, and the vibration can cause the change of capacity, especially for the high frequency bypass.
5, single stone capacitor
(multilayer ceramic capacitor) in a plurality of ceramic film coated with electrode material on the billet pitch after superposition, a circle formed one indivisible whole, outside use resin encapsulation and small volume, large capacity, high reliable and high temperature type capacitors, monolithic capacitors with high low frequency the dielectric constant also has stable performance, small size, high capacity Q value error noise bypass, filter, integral, oscillating circuit.
6, paper capacitor
Generally use two aluminum foil as the electrode, in the middle with a thickness of 0.008 ~ 0.012mm of the capacitor paper separated by overlapping winding. The manufacturing process is simple, the price is cheap, can get a large amount of capacity.
Generally in low frequency circuits, usually can not be higher than the frequency of 3 ~ 4MHz on the use of. The pressure of oil immersed capacitor than ordinary paper capacitor, good stability, suitable for high voltage circuit.
7, fine tuning capacitor
The capacitance can be adjusted in a small range, and can be fixed to a certain capacitance value after adjusting.
Ceramic capacitor has high Q value, and small size, usually can be divided into cylindrical tube and disc type two.
8, mica and polystyrene media are usually used in spring, the structure is simple, but the stability is poor.
Wire wound ceramic capacitor is removed to change the "outer" wire electrode capacitance, so the capacity can only become small, not suitable for repeated debugging in the occasion to use.
9, ceramic capacitor
With high dielectric constant ceramic capacitor on a titanium oxide, barium titanate is extruded into round tube, disc or disc as the medium, and the sintering method of silver plating on ceramics as electrode made. It is divided into high frequency and low frequency of two kinds of ceramic ceramic.
A capacitor with a small positive capacitance temperature coefficient is used for a high stability oscillation circuit, as a circuit capacitor and a pad capacitor. Low frequency ceramic capacitor is limited to a relatively low frequency circuit for bypass or DC blocking, or loss of stability and less demanding situations, including the "high frequency". This capacitor should not be used in the pulse circuit, because they are easy to be impulse voltage breakdown. High frequency ceramic capacitors for high frequency circuit.
Mica capacitor structure, can be divided into foil and silver type. Silver electrode directly on mica by vacuum evaporation or sintering method on silver plated layer, due to the elimination of the air gap, the temperature coefficient is reduced, stability is better than high capacitor foil. The frequency characteristic is good, the Q value is high, the temperature coefficient is small cannot make the large capacity to be widely applied in the high frequency electric appliance, and can be used as the standard capacitor.
10, glass glaze capacitor consists of a mixture of concentration suitable for special spraying into thin film and media, with a layer of silver electrode formed by sintering "monolith" structure performance can be comparable with the mica capacitor, can tolerate a variety of climate and environment, generally available at a temperature of 200 DEG C or higher rated work. The working voltage is 500V, the loss of 0.0005 ~ 0.008 TG.
Four, the main characteristics of the capacitor parameters:
1, nominal capacitance and allowable deviation
The nominal capacitance is the capacitance of the mark on the capacitor.
The deviation between the actual capacity of the capacitor and the nominal capacitance is referred to as the error, and the range of the allowable deviation is called the precision.
Precision grade and allowable error relationship: 00 + 1% (01) - (02) - 0, + 2%, + 5%, I - II - + 10%, + 20%, III - IV - (+20%-10%), V, VI - (+50%-20%) - (+50%-30%).
The general capacitor common I, II and III, IV, V, VI for electrolytic capacitor, based on the use of selected.
2, rated voltage
At the lowest temperature and the rated ambient temperature can be continuously and the highest DC voltage on the capacitor value, usually directly marked on the capacitor shell, if the working voltage of capacitor over voltage, capacitor breakdown, causing permanent damage can not be repaired.
3, insulation resistance
The DC voltage is added to the capacitor, and the leakage current is generated. The ratio of the two is called the insulation resistance.
When the capacitor is smaller, mainly depends on the surface state of the capacitor, the capacity of the 0.1uF, mainly depends on the performance of the medium, the smaller the insulation resistance, the better.
Capacitance time constant: the time constant is introduced for the proper evaluation of the insulation of the bulk capacitor, and the product of the insulation resistance and capacitance of the capacitor is equal to that of the capacitor.
Under the action of electric field, the energy consumed by the heat in the unit time is called the loss. Various types of capacitors are required to allow for a loss in a certain frequency range, the loss of the capacitor is mainly caused by the dielectric loss, the loss of electrical conductivity, and the resistance of all metal parts of the capacitor.
In the DC electric field, there is, the loss of the capacitor to the leakage loss form is generally small, under alternating electric field, the capacitance loss is not only related with the leakage, but also with the process of establishing the relevant periodic polarization.
5, frequency characteristics
With the increase of frequency, the capacitance of the average capacitor presents the law of decreasing.
Five, capacitor capacity marking
1, direct standard method
With numbers and unit symbols directly. Such as 01uF said 0.01 micro method, some capacitors with "R" to represent the decimal point, such as R56 said 0.56 micro method.
2, character symbol method
A combination of numbers and characters to represent the capacity. Such as P10 said 0.1pF, 1p0 said 1pF, 6P8 said 6.8pF, 2u2 said 2.2uF.
3, color method
The main parameters of the capacitor are represented by the color ring or the color point. The color method is identical with the resistor capacitor.
Capacitor deviation symbol: +100%-0--H, +100%-10%--R, +50%-10%--T, +30%-10%--Q, +50%-20%--S, +80%-20%--Z.