Capacitors are almost indispensable energy storage elements in electronic circuits. They have the characteristics of blocking DC, communicating with AC, and blocking low frequencies. Widely used in coupling, blocking, bypass, filtering, tuning, energy conversion and automatic control circuits. The next small series for everyone to introduce the role of capacitors and capacitor types.
The role of the capacitor
Capacitors in the circuit have DC blocking and AC switching functions, and are therefore often used in applications such as inter-stage coupling, filtering, decoupling, bypassing, and signal tuning. For example, in an audio circuit, how to more effectively use different types of capacitors has a great influence on the improvement of the sound quality of the audio. The capacitor usually functions as a filter, a coupler, a bypass, and a frequency divider. The equivalent circuit model of the capacitor is shown in Fig. 1. Among them, the equivalent series resistance (ESR) is mainly generated by the electrode lead and connection heat generation; the equivalent series inductance (ESL) is determined by the capacitor's package type, surface mount package and The ESL of a small SMD package is better; the leakage resistance (RLEAK) is closely related to the type of dielectric.
The principle of the capacitor
This is based on the structure of the capacitor. The simplest capacitor consists of a plate at both ends and an intermediate insulating dielectric (including air). After energization, the plate is charged, forming a voltage (potential difference), but due to the intermediary of the insulating material, the entire capacitor is not conductive. However, such a situation is under the premise of not exceeding the critical voltage (breakdown voltage) of the capacitor.
In AC circuits, the direction of the current changes as a function of time. The process of charging and discharging the capacitor is time-consuming. At this time, a changing electric field is formed between the plates, and the electric field is also a function of time. In fact, the current passes through the capacitor in the form of a field.
Kind of capacitor
1, paper capacitors
Two sheets of metal foil are used as electrodes, which are sandwiched between extremely thin capacitive papers, rolled into cylindrical or flat cylindrical cores, and then sealed in shells made of metal shells or insulating materials (such as paints, ceramics, glass glaze, etc.). It is characterized by its small size and large capacity. However, there are inherently large inductances and losses, which are more suitable for low frequencies.
2. Mica capacitors
The electrode plate is made by spraying silver layer on the metal foil or on the mica plate, the electrode plate and the mica layer are stacked one on another, and then die-casted in bakelite powder or sealed in epoxy resin. It is characterized by small dielectric loss, high insulation resistance and small temperature coefficient, and is suitable for high-frequency circuits.
3, ceramic capacitors
Using ceramics as a medium, a silver layer is sprayed on both sides of the ceramic substrate, and then a silver film is fired to make a polar 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 capacitors have a large capacity, but have a large loss and temperature coefficient and are suitable for use in low-frequency circuits.
4, film capacitance
The structure and paper capacitor are the same, the medium is polyester or polystyrene. Polyester film capacitors, high dielectric constant, small size, large capacity, good stability, suitable for bypass capacitors. Polystyrene film capacitors, small dielectric loss, high insulation resistance, but large temperature coefficient, can be used for high-frequency circuits.
5, metallized paper capacitors
Structure and paper capacitance are basically the same. It is to replace the metal foil with a metal film on the capacitor paper. It is small and has a large capacity. It is generally used in low-frequency circuits.
6, oil-impregnated paper capacitor
It is a paper dielectric capacitor immersed in specially treated oil, can enhance its pressure resistance. It is characterized by large capacity, high pressure, but large in size.
7, Aluminum Electrolytic Capacitors
It is made of aluminum cylinder anode, which is filled with liquid electrolyte, made by inserting a curved strip of aluminum as a positive electrode. Also need to go through the direct current voltage treatment, make the anode film form a layer of oxide film as the medium. It is characterized by large capacity, but large leakage current, poor stability, positive and negative polarity, suitable for power supply filtering or low frequency circuits. When using, do not reverse the positive and negative poles.
Editor's summary: The role of the capacitor and the type of capacitor are introduced here, and I hope to help everyone. If you want to know more related information, you can pay attention to this website information.
Capacitive switch
