Electrolytic capacitors are commonly known as polarized capacitors, in which the anode has more positive voltage than the cathode. They are used in filtering applications, low-pass filters, audio amplifier circuits and more. Metals such as aluminum, tantalum, niobium, and manganese form an oxide layer during the electrochemical process, which prevents current flow in one direction, but allows current flow in the opposite direction. This phenomenon was first observed in 1857 by the German physicist and chemist Johann Heinrich Buff (1805–1878). In 1875, French researcher and founder Eugene Ducretet was the first to realize this idea and invented the term "valve metal" for these.　　Electrolytic capacitors are mainly used when a small volume of high charge storage is required. In an electrolytic capacitor, the liquid electrolyte serves as one of the electrodes (mainly as the cathode). In order to better understand the concept of electrolytic capacitors. A capacitor is an electronic device that stores electrical charge. It consists of two conductive plates separated by an insulating material called a dielectric. Different types of insulating materials are used to construct the dielectric according to the application. The conductive plate of a capacitor is a good conductor of electricity. Therefore, they are easy to let current through. On the other hand, dielectrics or materials are poor conductors of electricity. Therefore, it does not allow current to pass.

1. Features

(1) The capacitance per unit volume is very large, tens to hundreds of times larger than other types of capacitors.

(2) The rated capacity can be very large, and it can easily be tens of thousands of μf or even a few f (but not comparable to the electric double layer capacitance).

(3) The price has an overwhelming advantage over other types, because the constituent materials of 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 produced on a large scale with relatively low cost.

2. Working principle

The dielectric of a polar electrolytic capacitor is an oxide film, which is similar to the PN junction in a transistor and has unidirectional conductivity. When the positive pin of the electrolytic capacitor is connected to a high potential and the negative pin to a low potential, the oxide film is in a blocking state, as if the PN junction is in a reverse bias state, the current between the positive and negative substrates is small, and the electrolytic capacitor is normal Work.

When the negative pin is connected to a high potential and the positive pin is connected to a low potential, the oxide film is in a state of flow, just like the forward conduction of a PN junction, the current between the two plates is very large, and the function of the capacitance will be lost. Pay attention to this If the positive and negative terminals of the capacitor are connected reversely, it will stop working and the machine will not work.

The polarity of the capacitor is due to the internal structure. There is a PN junction inside it. Only when a reverse voltage is applied to this PN junction, a polarized electrolytic capacitor can work normally.

3. Effect

(1) Filtering function. In the power circuit, the rectifier circuit turns AC into pulsating DC, and a larger capacity electrolytic capacitor is connected after the rectifier circuit, and its charge and discharge characteristics are used to make the rectified pulsating DC voltage change Into a relatively stable DC voltage.

In practice, in order to prevent the supply voltage of each part of the circuit from changing due to load changes, electrolytic capacitors of tens to hundreds of microfarads are generally connected to the output end of the power supply and the power input end of the load. Since large-capacity electrolytic capacitors generally have a certain inductance and cannot effectively filter out high-frequency and pulse interference signals, a capacitor with a capacity of 0.001--0.lpF is connected in parallel at both ends to filter out high-frequency And pulse interference.

(2) Coupling: In the process of low-frequency signal transmission and amplification, in order to prevent the static operating points of the front and rear two stages of circuits from interacting with each other, capacitive coupling is often used. In order to prevent excessive loss of low-frequency components in the rhyme of the signal, electrolytic capacitors with larger capacity are generally used.

(Summarized by Easybom: https://www.easybom.com )