Functions of capacitors types of capacitors

  • Detail

The capacitor can store charge and has the function of isolating DC. When the two electrode plates of the capacitor are connected to the positive and negative electrodes of the DC power supply respectively, the positive and negative charges will gather on the two electrode plates of the capacitor and form a voltage between the two electrode plates

capacitor is almost an indispensable energy storage element in electronic circuits. It has the characteristics of blocking DC, connecting AC and preventing low frequency. It is widely used in coupling, DC isolation, bypass, filtering, tuning, energy conversion and automatic control circuits. Next, I will introduce the functions and types of capacitors

function of capacitor

capacitor has the function of isolating DC and connecting AC in the circuit, so it is often used for interstage coupling, filtering, decoupling, bypass and signal tuning. For example, in the audio circuit, how to choose and use different types of capacitors more effectively has a great impact on the improvement of audio quality. Capacitors usually play the roles of filtering, coupling, bypass, frequency division and so on. The equivalent circuit model of capacitance is shown in Figure 1, in which the equivalent series resistance (ESR) is mainly generated by the heating of electrode leads and connections; The equivalent series inductance (ESL) depends on the package type of capacitor, and the ESL of surface mount package and small SMD package is better; The leakage resistance (rleak) is closely related to the type of dielectric

principle of capacitor

this must start from the structure of capacitor. The simplest capacitor is composed of plates at both ends and insulating dielectrics (including air) in the middle. After power on, the electrode plate is charged to form a voltage (potential difference), but due to the insulating material in the middle, the whole capacitor is non-conductive. However, such a situation is under the premise that the critical voltage (breakdown voltage) of the capacitor is not exceeded

in AC circuit, the direction of current changes as a function of time. The process of capacitor charging and discharging takes time. At this time, a changing electric field is formed between the plates, and this electric field is also a function of time. In fact, current flows between capacitors in the form of a field

types of capacitors

1. Paper dielectric capacitors

use two pieces of metal foil as electrodes, clamp them in extremely thin capacitor paper, roll them into cylindrical or flat cylindrical cores, and then seal them in metal shells or insulating materials (such as fire paint, ceramics, glass glaze, etc.) shells. It is characterized by small volume and large capacity. However, the inherent inductance and loss are relatively large, so it is more suitable for low frequency

2. Mica capacitor

use metal foil or spray silver layer on mica sheet as electrode plate. After the electrode plate and mica are laminated layer by layer, it is made by die-casting in bakelite powder or sealing in epoxy resin. It is characterized by low dielectric loss, large insulation resistance and low temperature coefficient, which is suitable for high-frequency circuits

3. Ceramic capacitor

it is made of ceramic as the medium, sprayed with silver layer on both sides of the ceramic matrix, and then burned into silver film as the electrode plate. It is characterized by small size, good heat resistance, low loss, high insulation resistance, but small capacity, suitable for high-frequency circuits. Ferroelectric ceramic capacitor has large capacity, but large loss and temperature coefficient, which is suitable for low-frequency circuits

4. The structure of film capacitor is the same as that of paper capacitor, and the medium is polyester or polystyrene. Polyester film capacitor, with high dielectric constant, small volume, large capacity and good stability, is suitable for bypass capacitor. Polystyrene film capacitor, with low dielectric loss and high insulation resistance, but high temperature coefficient, can be used in high-frequency circuits

5. The structure of metallized paper capacitor is basically the same as that of paper capacitor. It is coated with a layer of metal film on the capacitor paper to replace the metal foil. It has small volume and large capacity, and is generally used in low-frequency circuits

6. Oil immersed paper capacitor

it immerses the paper capacitor in specially treated oil, which can enhance its withstand voltage. It is characterized by large capacitance, high voltage resistance, but large volume

7. Aluminum electrolytic capacitor

it is made of an aluminum cylinder as the negative pole, which is filled with liquid electrolyte and inserted with a curved aluminum strip as the positive pole. It also needs to be treated with DC voltage to form a layer of oxide film on the positive plate as the medium. It is characterized by large capacity, but large leakage, poor stability, and positive and negative polarity. It is suitable for power filtering or low-frequency circuits. When using, the positive and negative poles should not be reversed

editor's summary: This is the introduction of the function and types of capacitors. I hope it will be helpful to you. If you want to know more about it, you can pay attention to the information




Copyright © 2011 JIN SHI