The basic profile 1 of aluminum electrolytic
capacitor.
The basic principle of the basic principle of capacitor capacitor can be used in figure 1 -
1 to describe when on the metal electrodes of the two is the applied voltage, the charge will be stored according to the size of the voltage of Q = CVQ: power (
C)
V: voltage (
V)
C: electric capacity (
FC: electric capacity of capacitor, can by the electrode area S [
m2]
, medium thickness t [
m]
As well as the relative dielectric constant & epsilon;
To represent the C [
F]
= ε
0?
ε
吗?
S / tε
0: medium under the vacuum state of dielectric constant (
= 8.
85 x10 -
12 F/M)
Aluminum oxide film of relatively dielectric constant of 7 ~ 8, in order to get a larger capacitance, can increase the surface area S t to gain or reduce its thickness.
Table 1 lists the commonly used several kinds of typical medium in the capacitor of the relative dielectric constant, in many cases, the naming of capacitor is usually based on medium to determine the use of materials, such as: aluminum electrolytic capacitors, tantalum capacitors, etc.
Table 1 relative dielectric constant relative dielectric constant 10 ~ 12010 ~ 20 while aluminum electrolytic capacitor is very small, but it has a relatively large capacitance, because his through electrochemical corrosion, the surface area of the electrode foil was expanded, and it's very thin oxide film.
Figure 2 vividly describes the basic components of aluminum electrolytic capacitors.
2 capacitor equivalent circuit diagram of the equivalent circuit of capacitor can be represented by the following figure 2 R1: the resistance of the electrode and leading-out terminal R2: anodic oxide film and the electrolyte resistance R3: damage to the insulation resistance of anodic oxide film of D1: with unidirectional conductivity of anodic oxide film C1: capacity of anode foil C2: the capacity of the cathode foil L: caused by electrode and lead terminal 3 basic electrical 3 - equivalent inductance
1 electric capacity of capacitor is decided by measure the impedance of the exchange capacity presented.
Alternating current capacity varies with frequency, voltage and measuring method.
Aluminum electrolytic capacitor capacity decreases with the increase of frequency.
And frequency, the temperature at which the measurement has a certain influence on the capacity of the capacitor.
As the measured temperature drop, the capacity will be smaller.
On the other hand, direct current capacity, can be obtained by applying a dc voltage and measuring the charge, at room temperature capacity than the exchange of a bit bigger, and more superior stability characteristics.
1 -
3 -
2 Tan δ
(
The loss tangent)
In equivalent circuit, the equivalent series resistance ESR with capacitive reactance 1 / wC is called Tan & delta;
, the same as the capacitance measurement conditions.
tan δ
= RESR / (
1 / wC)
= wC RESR: RESR = the ESR (
120 Hz)
w=2π
ff=120Hztan δ
Increased with the increase of frequency measurement, along with the decline of measuring temperature increase.
Impedance (
Z)
: under the specific frequency, hinder the impedance of the alternating current through the resistor is called (
Z)
。
It is closely related to the capacity and inductance, and also has relations with the equivalent series resistance ESR.
Specific expression is as follows: including: Xc = 1 / wC = 1/2 & PI;
fCXL=wL=2π
FL: leakage current of dc capacitor medium has great effect.
However, due to the aluminum oxide film medium with electrolyte, when the applied voltage, the formation and repair of oxide film can create a very small called leakage current, just when the applied voltage, leakage current is larger, with the extension of time, the leakage flow gradually decrease and eventually remained stable.
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