The difference and usage between polar capacitance and non-polar capacitance

Capacitors generally have no polarity. With the development of science and technology and the exploration of new materials, more high-quality and diversified capacitors will emerge, such as polar capacitors and non-polar capacitors. Although the principle of polar capacitance and non-polar capacitance is the same, they are different from the different media, performance, capacity and structure, resulting in different use environments and purposes. This article introduces the similarities and differences between the two and whether they can replace each other from eight points.

1. Same principle

(1) Both store and release charges;

(2) The voltage on the electrode plate (here the electromotive force of charge accumulation is called voltage) cannot be sudden changed.

(3) The difference lies in different media, different performance, different capacity and different structure, resulting in different use environments and purposes.

On the other hand, according to the needs of production practice, people have manufactured various functional capacitors to meet the normal operation of various electrical appliances and the operation of new equipment. With the development of science and technology and the discovery of new materials, more high-quality and diversified capacitors will continue to emerge.

The difference and usage between polar capacitance and non-polar capacitance

2. Different concepts

Polar capacitance refers to the capacitance of electrolytic capacitor, which is composed of two electrodes formed by the aluminum foil of anode and the electrolyte of cathode, and a layer of aluminum oxide film produced on the aluminum foil of anode as the dielectric.

A non-polar capacitor is a capacitor without the positive and negative poles of the polar power supply. The two electrodes of the non-polar capacitor can be connected in the circuit at will.

3. Different media

What is media? To put it bluntly, it is the material between the two plates of the capacitor. Most of the polar capacitors use electrolyte as the dielectric material. Usually, the capacitance with the same volume has large capacity. In addition, the capacity of the same volume of the polar capacitor produced by different electrolyte materials and processes will also be different. Moreover, there is a close relationship between pressure resistance and the use of dielectric materials. There are also many non-polar capacitor dielectric materials, most of which are metal oxide film, polyester, etc. The reversible or irreversible performance of the medium determines the use environment of polar and non-polar capacitors.

4. Different performance

Performance is the requirement of use, and demand maximization is the requirement of use. If a metal oxide film capacitor is used for filtering in the power supply part of the TV set, the capacity and withstand voltage of the capacitor required for filtering should be met. I'm afraid only one power supply can be installed in the enclosure. Therefore, as a filter, only polar capacitance can be used, which is irreversible. That is to say, the positive pole must be connected to the high potential terminal and the negative pole must be connected to the low potential terminal. Generally, the electrolytic capacitor is more than 1 microfarad, which is used for coupling, decoupling, power filter, etc. Most of the non-polar capacitors are less than 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 for reactive power compensation of electric power, phase shift of motor, frequency conversion power shift and other purposes. There are many kinds of non-polar capacitors, which will not be described one by one.

5. Different capacities

As mentioned earlier, capacitor media of the same volume have different capacities, so I won't repeat them one by one.

6. Different structure

In principle, without considering the tip discharge, any shape of capacitor required by the use environment can be used. The electrolytic capacitor (with polarity) usually used is round, and the square type is rarely used. The shape of the nonpolar capacitor varies greatly. Like tube shape, deformed rectangle shape, sheet shape, square shape, round shape, combined square shape and round shape, etc., depending on where it is used. Of course, there is also invisible. Here, invisible refers to distributed capacitance. The distributed capacitance cannot be ignored in high-frequency and intermediate frequency devices.

7. Use environment and purpose

Because of the relationship between its internal material and structure, the capacity of the polar capacitor (such as aluminum electrolysis) can be very large, but its high-frequency characteristics are not good, so it is suitable for power filter and other occasions, but there is also a polar capacitor with good high-frequency characteristics - tantalum electrolysis, which is relatively high in price;

The non-polar capacitor has small size, low price and good high-frequency characteristics, but it is not suitable for large capacity. For example, ceramic chip capacitors, monolithic capacitors, polyethylene (CBB) capacitors, etc., ceramic chip capacitors are generally used in high-frequency filtering and oscillation circuits.

Magnetic dielectric capacitor is a capacitor with ceramic material as the meson and silver layer as the electrode on the surface. The magnetic dielectric capacitor has stable performance. The loss and leakage are very small, which is suitable for application in high-frequency and high-voltage circuits.

Generally speaking, the insulating materials between the two poles of the capacitor with large dielectric constant (such as ferroelectric ceramics and electrolyte) are suitable for making large-capacity and small-volume capacitors, but the loss is also large. Low dielectric constant (such as ceramic) loss, suitable for high-frequency applications.

8. Can they be replaced

The ideal capacitance is originally non-polar. But in practice, in order to obtain large capacity, some special materials and structures are used, which leads to the fact that some of the actual capacitance is polar. Common polar capacitors include aluminum electrolytic capacitor, tantalum electrolytic capacitor, etc. Electrolytic capacitors are generally of relatively large capacity. If we want to make a large-capacity non-polar capacitor, it is not so easy, and the volume will become large. This is why there are so many polar capacitors in the actual circuit - because it is relatively small, and because the voltage in such a circuit has only one direction, the polar capacitor can be used. We use a polar capacitor to avoid its disadvantages and take advantage of its advantages. We can understand that a polar capacitor is actually a capacitor that can only be used in one voltage direction. The non-polar capacitor can be used in both voltage directions. Therefore, from the point of voltage direction alone, non-polar capacitance is better than polar capacitance.