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The difference between polarized capacitors and non-polarized capacitors in performance, principle and structure

Date: 2024-07-19
Polarized capacitors refer to capacitors such as electrolytic capacitors. They are composed of two electrodes, the aluminum foil at the anode and the electrolyte at the cathode, and a layer of aluminum oxide film on the anode aluminum foil as the dielectric. Due to this structure, it has polarity. When the capacitor is connected in the positive direction, the aluminum oxide film will remain stable due to the electrochemical reaction. When it is connected in the reverse direction, the aluminum oxide layer will become thinner, making the capacitor easy to be broken down and damaged. Therefore, the polarity of electrolytic capacitors must be paid attention to in the circuit. Ordinary capacitors are non-polar. You can also connect two electrolytic capacitors in series to form a non-polarized electrolytic capacitor.

1. The principle is the same.
(1) Both store and release charges;
(2) The voltage on the plate (here the electromotive force of accumulated charge is called voltage) cannot change suddenly.

(3) The difference lies in the different media, performance, capacity, and structure, resulting in different usage environments and uses. On the other hand, people have experimentally manufactured capacitors with various functions to meet the normal operation of various electrical appliances and the operation of new equipment according to the needs of production practice. With the development of science and technology and the discovery of new materials, better and more diversified capacitors will continue to emerge.

2. Different dielectrics.

What is a dielectric? To put it bluntly, it is the material between the two plates of a capacitor. Most polar capacitors use electrolytes as dielectric materials, and usually the same volume of capacitors has a larger capacity. In addition, the capacity of polar capacitors with the same volume manufactured by different electrolyte materials and processes will also be different. Another thing is that the withstand voltage is closely related to the use of dielectric materials. There are also many dielectric materials for non-polar capacitors, most of which use metal oxide films, polyester, etc. The reversible or irreversible properties of the dielectric determine the use environment of polar and non-polar capacitors.

3. Different performance.

Performance is the requirement for use, and maximizing demand is the requirement for use. If a metal oxide film capacitor is used for filtering in the power supply part of a TV, and the capacitor capacity and withstand voltage required for filtering must be achieved. I'm afraid that only a power supply can be installed in the casing. Therefore, only polarized capacitors can be used for filtering, and polarized capacitors are irreversible. That is to say, the positive pole must be connected to the high potential end, and the negative pole must be connected to the low potential end. Generally, electrolytic capacitors are above 1 microfarad, and are used for coupling, decoupling, power supply filtering, etc. Non-polarized capacitors are mostly below 1 microfarad, and participate in resonance, coupling, frequency selection, current limiting, etc. Of course, there are also large-capacity and high-voltage ones, which are mostly used in power reactive power compensation, motor phase shifting, variable frequency power supply phase shifting, etc. There are many types of non-polarized capacitors, and I will not go into details one by one.

4. Different capacity.

It has been mentioned before that capacitors of the same volume have different capacities with different dielectrics, so I will not go into details one by one.

5. Different structures. In principle, without considering the tip discharge, any shape of capacitor required by the use environment can be used. The commonly used electrolytic capacitors (polarized capacitors) are round, and square ones are rarely used. Non-polarized capacitors have a variety of shapes. Like tube type, deformed rectangle, sheet type, square type, round type, combined square type and round type, etc., see where it is used. Of course, there are invisible ones, and the invisible here refers to distributed capacitance. Distributed capacitance must not be ignored in high-frequency and medium-frequency devices.

The function is the same. The main difference is in capacity. Affected by the material structure, the capacity of non-polar capacitors is generally small, generally below 10uF, while the capacity of polar capacitors is generally larger. For example, when filtering the power supply, you have to use large-capacity polar capacitors.

A basic principle of circuit design is to require designers to fully understand and master the components in reality. The components used should be standard parts and universal parts as much as possible, and preferably the most common models on the market (the better the universality of the components, the easier it is to purchase, the larger the supplier's output, and the lower the procurement cost).

Decoupling is only one of the functions of capacitors. Capacitors have other functions. Different types of capacitors have very different characteristics and usages. The capacitor on the schematic diagram is just a symbol. There are many skills behind it. This aspect is closely related to experience. It is impossible to achieve quick success, and it can only be accumulated slowly through practice.
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