Basic summary of aluminum electrolytic capacitor

1-1. Basic Principles of Capacitors The basic principle of a capacitor can be described using Figure 1-1. Original Position Original Position When a voltage is applied to two metal electrodes facing each other, the charge is stored according to the voltage. The original position
Q=CV

Fig. 1-1 Original position
Q: Power (C) Original Position
V: voltage (V) original position
C: Capacity (F

C: The capacitance of the capacitor, which can be represented by the electrode area S [m2], the dielectric thickness t [m], and the relative permittivity ε

C[F] = ε0·ε·S/t Original position ε0: Dielectric constant of medium under vacuum (=8.85x10-12 F/M) Original position Original position The relative permittivity of aluminum oxide film is 7~ 8, In order to obtain a larger capacitance, it can be obtained by increasing the surface area S or decreasing its thickness t. Original position The original position Table 1-1 lists the relative dielectric constants of several typical media commonly used in capacitors. In many cases, the name of the capacitor is usually determined by the material used in the media, for example: aluminum electrolysis. Capacitors, tantalum capacitors, etc.

Table 1-1

Although the Aluminum Electrolytic Capacitor is very small, it has a relatively large capacitance because the surface area of the electrode foil is enlarged after electrochemical etching, and its dielectric oxide film is very thin. Original Position Figure 1-2 shows the basic composition of an aluminum Electrolytic capacitor.

Original location

Figure 1-2

Original Position 1-2 Capacitor Equivalent Circuit Original Position Original Position Capacitor Equivalent Circuit Diagram The following figure 2 shows the original position

figure 2

R1: The resistance of the electrodes and terminals
R2: Anodic Oxidation Film and Electrolyte Resistance Original Position
R3: Insulation Resistance of Damaged Anodized Film Original Position
D1: Anodized Film with Unidirectional Conductivity Original Position
C1: Anode Foil Capacity Original Position
C2: Cathode Foil Capacity Original Position
L : equivalent inductance caused by electrodes and lead terminals

1-3 Basic Electrical Properties Original Position Original Position 1-3-1 Electrical Capacity Original Position Original Position The capacitor is determined by the impedance exhibited when measuring the AC capacity. AC capacitance changes with frequency, voltage, and measurement methods. The capacity of Aluminum Electrolytic Capacitors decreases with increasing frequency.

As with frequency, the temperature at the time of measurement has a certain influence on the capacity of the capacitor. As the measured temperature drops, the capacitance becomes smaller.

On the other hand, the DC capacity can be obtained by measuring the charge by applying a DC voltage. At room temperature, the capacity is slightly larger than that of AC, and it has superior stability characteristics.

1-3-2 Tan δ (loss tangent) Original Position Original Position In the equivalent circuit, the ratio of series equivalent resistance ESR to capacitive reactance 1/wC is called Tan δ. The measurement conditions are the same as the capacitance.

Original location Original location
Tan δ = RESR / (1/wC) = wC RESR Original position where: RESR = ESR (120 Hz) Original position
w=2πf Original position
f=120Hz Original position
The tan δ becomes larger as the measurement frequency increases, and increases as the measurement temperature decreases. Original Position Impedance (Z): Original Position Original Position At a specific frequency, the impedance that blocks the flow of alternating current is the so-called impedance (Z). It is closely related to the capacity and inductance, and also related to the equivalent series resistance ESR. The specific expression is as follows:

Where: Xc=1/ wC=1/ 2πfC Original position
XL = wL = 2πfL Original Position Leakage Current: Original Position Original Position The dielectric of the capacitor has a significant impediment to direct current. However, since the aluminum oxide film is impregnated with an electrolyte, when the voltage is applied, a small current called a leakage current is generated when the oxide film is reformed and repaired. When the voltage is applied, the leakage current is large. As time goes by, the leakage current will gradually decrease and remain stable over time.

Original position leakage current characteristics map

Test temperature and voltage have a great influence on leakage current. Leakage current increases with temperature and voltage