Electrolytic Capacitor

What is an electrolytic capacitor?
Electrolytic capacitors have electrolyte materials that store charges inside, which are divided into positive and negative polarities, similar to batteries, and cannot be reversed. The positive electrode is a metal substrate with an oxide film, and the negative electrode is connected to the electrolyte (solid and non-solid) through a metal plate.
Nonpolar (bipolar) electrolytic capacitors use a double oxide film structure, which is similar to two polarized electrolytic capacitors with two negative poles connected. The two electrodes are connected by two metal plates (both with oxide films), and the electrolyte is in the middle of the two sets of oxide films. Polar electrolytic capacitors usually play the role of power filtering, decoupling (ǒu), signal coupling, time constant setting, and DC blocking in power circuits or intermediate frequency and low frequency circuits. Non-polar electrolytic capacitors are usually used in audio frequency divider circuits, TV S correction circuits and starting circuits for single-phase motors.

Product Introduction of Electrolytic Capacitors
The working voltage of electrolytic capacitors is 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 160V, 200V, 300V, 400V, 450V, 500V. The working temperature is -55°~+155°C (4~500V). It is characterized by large capacity, large volume, and polarity. It is generally used for filtering and rectifying in DC circuits. The most commonly used electrolytic capacitors are aluminum electrolytic capacitors and tantalum electrolytic capacitors.

Electrolytic Capacitor Characteristic Parameters
Nominal capacitance and allowable deviation
Nominal capacitance is the capacitance marked on the capacitor.
The basic unit of capacitors is farad (F), however, this unit is too large and is rarely used in field marking.
Other unit relations are as follows:
1F=1000mF
1mF=1000μF
1μF=1000nF
1nF=1000pF
The deviation between the actual capacitance of the capacitor and the nominal capacitance is called the error, and the deviation within the allowable range is called the accuracy.
Correspondence between accuracy level and allowable error: 00(01)-±1%, 0(02)-±2%, Ⅰ-±5%, Ⅱ-±10%, Ⅲ-±20%, Ⅳ-(+20% -10%), Ⅴ-(+50%-20%), Ⅵ-(+50%-30%)
Generally, capacitors are commonly used in grades I, II, and III, and electrolytic capacitors are used in grades IV, V, and VI, which are selected according to the application.

Rated voltage of electrolytic capacitor
The highest effective value of DC voltage that can be continuously applied to the capacitor at the lowest ambient temperature and the rated ambient temperature is usually marked directly on the capacitor shell. If the operating voltage exceeds the withstand voltage of the capacitor, the capacitor will break down, causing irreparable permanent damage.

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Insulation Resistance of Electrolytic Capacitors
The DC voltage is added to the capacitor and generates a leakage current. The ratio between the two is called the insulation resistance.
When the capacitance is small, it mainly depends on the surface state of the capacitance. When the capacity is >0.1uf, it mainly depends on the performance of the medium, and the larger the insulation resistance, the better.
Capacitor time constant: The time constant is introduced to properly evaluate the insulation of large-capacity capacitors, which is equal to the product of the capacitor's insulation resistance and capacity.

Loss of electrolytic capacitor
Under the action of an electric field, the energy consumed by heat in a unit time is called loss. All types of capacitors specify their allowable loss values within a certain frequency range. The loss of the capacitor is mainly caused by the dielectric loss, the conductance loss and the resistance of all metal parts of the capacitor.
Under the action of DC electric field, the loss of capacitor exists in the form of leakage conduction loss. Generally small, under the action of alternating electric field, the loss of capacitance is not only related to leakage conduction, but also related to the periodic polarization process.

Frequency Characteristics of Electrolytic Capacitors
As the frequency increases, the capacitance of a general capacitor shows a decreasing trend.
The structural characteristics of aluminum electrolytic capacitors:
The aluminum shell and rubber cover are sealed together to form an electrolytic capacitor. Compared with other types of capacitors, aluminum electrolytic capacitors show the following obvious characteristics in structure:
(1) The working medium of aluminum electrolytic capacitors is to form an extremely thin layer of aluminum oxide (Al2O3) on the surface of aluminum foil by anodic oxidation. The oxide dielectric layer and the anode of the capacitor are combined into a complete system, and the two are interdependent and cannot be independent of each other. What we usually call a capacitor, its electrodes and dielectric are independent of each other.
The core of an aluminum electrolytic capacitor is made of 4 overlapping layers of anode aluminum foil, electrolytic paper, cathode aluminum foil, and electrolytic paper;
(2) The anode of the aluminum electrolytic capacitor is an aluminum foil with an Al2O3 dielectric layer on the surface, and the cathode is not the negative foil we are used to, but the electrolyte of the capacitor.
(3) The negative foil has the function of electrical extraction in the electrolytic capacitor. Because the electrolyte used as the cathode of the electrolytic capacitor cannot be directly connected to the external circuit, an electrical path must be formed through another metal electrode and other parts of the circuit.
(4) The anode aluminum foil and cathode aluminum foil of aluminum electrolytic capacitors are usually corroded aluminum foil, and the actual surface area is much larger than its apparent surface area. This is one reason why aluminum electrolytic capacitors usually have a large capacitance. Due to the use of aluminum foil with many fine pits, liquid electrolyte is usually required to more effectively utilize its actual electrode area.
(5) Since the dielectric oxide film of aluminum electrolytic capacitors is obtained by anodic oxidation, and its thickness is proportional to the voltage applied by anodic oxidation. Therefore, in principle, the thickness of the dielectric layer of an aluminum electrolytic capacitor can be precisely controlled artificially.