简介
无极性电容是电容的一种。根据是否具有极性，电容可以分为有极性电容和无极性电容。
本文下面主要讲解：
- 什么是无极性电容；
- 它有什么作用？
- 如何挑选无极性电容？
- 在电解电容与无极性电容之间有什么区别？
基本概念
无极性电容的两个引脚之间不具有正负极之分，它们可以按任意顺序连接到电路中，不会造成反向电解液溢出。
无极性电容主要应用于耦合、解耦，反馈、补偿以及振荡电路中。下面图显示了一种无极性电容的外观：
基本应用
无极性电容通常应用在纯交流电路中。由于它的容量往往比较小，所以适合应用于高频滤波电路。下面给出几种无极性电容的应用例子。
1. 电火花脉冲吸收电路
应用阻容（RC）串联电路实现尖脉冲抑制电路。比如在荧光灯点亮过程中，会产生比较强的尖脉冲干扰信号，通过天线窜入收音机或者电视接收机中会产生不规则声响，或者在电视屏幕上产生亮斑，亮条纹等。这都是由于尖脉冲信号所引起的杂乱干扰信号。
在具有电感回路中，如果突然断开，在开关触点之间会产生电火花。如下图所示。当电路中的开关S突然断开，电流终止。如果电流很大的情况下，根据电感的自感效应，就会在电感两端产生很好的脉冲电压。该电压与电源电压U1叠加在一起施加在开关S两端，超过一定阈值之后，就会击穿开关接触点之间的空气形成电火花。
带有电感的电路以及电火花吸收电路
2. 工作原理
电火花引起开关触点的烧蚀和氧化，从而引起开关失效，所以需要通过吸收电路来保护开关触点。如果能够使得电路电流下降速度减弱，回路中电感所产生的感应电动势就会降低，从而避免产生电火花。
使用RC串联电路并联在电感的两端，当电路中开关关断是，电流就会通过RC进行流动，一部分电感中的磁场能量就会消耗在RC回路中的电阻上和电感内部电阻上，一部分存储在电容上。这样就避免了高压电火花的产生。
无极性电容的选择
应用无极性电容非常方便。选择具有相同规格的电容可以相互替换。
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对于电火花吸收电路中的电容容量一般相对比较小，对于容量精度要求不高，只要差不多相同的电容都可以使用。当然耐压需要留有余量；
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用于振荡电路中、延时定时电路、调谐电路中的电容则需要电容的精度误差在0.3~0.5%之内；
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根据电路要求选择不同材质的电容。纸质电容通常应用于低频电路。石英电容，或者陶瓷电容可以应用于高频电路，或者高压电路中；
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电容的耐压需要选择大于等于实际工作电压。
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高频电容不允许使用低频电容替代；
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考虑工作温度环境，需要按照实际工作环境选择不同温度等级的电容；
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如果容量或者耐压不够，可以通过串联或者并联来达到要求。
不同种类的电容
无论有极性还是无极性电容，它们都是通过充放电原理来工作的。施加在两个电极之间的电压（造成电荷积累在两个电极上的电动势）不能够突然改变。
根据应用环境和用途，选择不同材质、不同性能、不同容量以及不同结构的电容。随着科技的发展和新材料的产生，更多质优电容器会不断涌现。
不同类型的无极性电容
1. 不同的电介质
什么事电介质，就是在两个电容极板之间的绝缘物质。很多有极性电容使用电解液作为电介质。，这样就会产生比其他无极性电容在相同的体积下大得多的电容容量。
另外，有极性电容使用不同的电解物质会有不同的容量。电容的耐压也与电容材料有关系。很多无极性电容使用金属氧化薄膜或者聚酯薄膜。是否电容具有极性取决于电介质的本性是否可逆。
2. 不同的性能
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Different performance
Performance and the demand maximization is the requirement of use. If the power supply of the TV use metal oxide film capacitor as filter, and if the capacitance and voltage withstand are required to meet the filter, I’m afraid only a power supply can be installed inside the shell. Therefore, filter can only use polarity capacitor, and polarity capacitance is irreversible. Generally, the electrolytic capacitor is above 1 MF, which participates in coupling, decoupling, power supply filtering and so on. The non-polar capacitor is mostly below 1 MF, which is involved in resonance, coupling, frequency selection, current limiting and so on. Of course, there are also non-polar capacitors with large capacity and high voltage, mostly used in reactive power compensation, motor phase shifting, frequency conversion power phase shifting and other purposes. There are many kinds of non-polarized capacitors.
有极性电解电容 -
Different capacity
As I have mentioned before, capacitors of the same volume have different capacitance under different dielectric .
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Different structure
In principle, it is possible to use a capacitor of any shape in the environment without considering the point discharge. The most using electrolytic capacitors are circular, and the square type is rare. The shape of capacitors are varied, such as tubular, deformed rectangular, sheet, square, circular, combined square or circular and so on, depending on where they are used. Of course, there is also invisible ones called distributed capacitor, which must not be ignored in high frequency and intermediate frequency devices.
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Using environment and usage
Because of the internal material and structure, polarity capacitor (such as aluminum electrolysis) capacity can be very large, but its high-frequency characteristics are not good, so it is suitable for power filter and other occasions. There are also polarity capacitors of good high-frequency characteristics - tantalum electrolysis, whose price is relatively high;
Including ceramic capacitors, monolithic capacitors, polyethylene (CBB) capacitors and so on, these non polarized capacitors are small in size, low in price and good in high-frequency characteristics, but they are not suitable for the large capacity. Ceramic capacitors are generally used in high-frequency filtering, oscillation circuit.
无极性电容
The magnetic dielectric capacitors use ceramic material as meson and use silver layer on the surface as electrode. Having stable performance and small leakage, the magnetic dielectric capacitors are suitable to apply in high frequency and high voltage circuits.
Generally speaking, according to the insulating material between the two poles of capacitor. Material with large dielectric permittivity (such as ferroelectric ceramics, electrolyte) is suitable for capacitors of large capacity and small volume, whose loss is also large. Material with small dielectric permittivity (such as ceramics) has a low loss and is suitable for high frequency applications.
