Mica capacitance

The electrode plate is made of metal foil or silver layer sprayed on mica sheet. The electrode plate and mica are laminated one layer at a time and then die cast in formica powder or sealed in epoxy resin. It is characterized by small dielectric loss, large insulation resistance, small temperature coefficient, suitable for high frequency circuit.

Ceramic capacitance

Using ceramic as medium, silver layer is sprayed on both sides of ceramic matrix, and then burnt into silver film as plate. It is characterized by small size, good heat resistance, small loss, high insulation resistance, but small capacity, suitable for high frequency circuit. Ferroelectric ceramics are suitable for low frequency circuit because of their large capacitance and high loss and temperature coefficient.

Paper capacitor

The electrodes are made of two metal foils, sandwiched in extremely thin capacitor paper, rolled into cylindrical or flat cylindrical cores, and then sealed in a metal shell or insulating material (such as lacquer, ceramic, glass glaze, etc.) shell. It is characterized by smaller volume, capacity can be made larger. But the inherent inductance and loss are relatively large, suitable for low frequency.

Thin film capacitance

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

Metallized paper capacitor

Structure and paper capacitor is basically the same. It is a capacitor paper covered with a layer of metal film instead of metal foil, small volume, large capacity, generally used in low-frequency circuits.

Semi-variable capacitance

Also called trimmer capacitor. It's made of two or more small pieces of metal shrapnel with medium between them. Adjust by changing the distance or area between the two pieces. Its medium has air, ceramics, mica, film and so on.

Oil impregnated paper capacitor

It is the paper capacitor dipped in specially treated oil, can enhance its voltage. It is characterized by large capacitance, high voltage, but large volume.

Aluminum electrolytic capacitor

It is made of an aluminum cylinder with a liquid electrolyte in it and inserted into a curved aluminum strip for a positive electrode. It also needs to be processed by DC voltage to form an oxide film on the positive electrode plate as a medium. It is characterized by large capacity, but large leakage, poor stability, positive and negative polarity, suitable for power filter or low frequency circuit. When in use, do not connect the positive and negative terminals.

Tantalum and niobium electrolytic capacitors

It is made of tantalum or niobium metal as a positive electrode, dilute sulfuric acid and other liquids as a negative electrode, with tantalum or niobium surface generated oxide film as a medium. It is characterized by small volume, large capacity, stable performance, long life, large insulation resistance, good temperature characteristics. Used in demanding equipment.

Variable capacitance

It consists of a group of fixed pieces and a group of moving pieces, and its capacity can be continuously changed with the rotation of the moving pieces. The two groups of variable capacitors assembled together coaxial rotation, called double connection. Variable capacitance medium has air and polystyrene two kinds. Variable capacitance of air medium has large volume and small loss, and is often used in vacuum tube radio. Polystyrene dielectric variable capacitor made of sealed, small size, used in transistor radio.

NPO(COG): The electrical performance is the most stable, basically does not change with the temperature, voltage and time change surface, suitable for high frequency circuit to seek high stability;

X7R(2X1): The electrical performance is stable, and the performance does not change significantly when the temperature, voltage and time change. It is suitable for direct separation, coupling, bypass and frequency discrimination circuits that do not require high capacity stability. Because X7R is a strong dielectric, capacitors with larger capacity than NPO dielectric can be made on the surface.

Y5V (2F4) (Z5U) : with low and high dielectric constant, it is often used in the production of large capacity capacitors with large specific capacity and high nominal capacity, but its capacity stability is worse than X7R, and its capacity and loss are more sensitive to temperature, voltage and other test conditions.

Three, the role of capacitance

1. Dc isolation: The function is to prevent the passage of DC and allow AC to pass.

2. Bypass (decoupling) : Provides a low impedance path for certain parallel components in an AC circuit.

3. Coupling: Acts as a connection between two circuits, allowing AC signals to pass through and be transmitted to the next circuit

4. Filtering: This is very important for DIY. The capacitors on the graphics cards are basically used for this purpose.

5. Temperature compensation: for the influence of other components on the temperature adaptability is not enough, and compensation, improve the stability of the circuit.

6. Timing: A capacitor is used in conjunction with a resistor to determine the time constant of a circuit.

7. Tuning: Systematic tuning of frequency-dependent circuits, such as cell phones, radios, and television sets.

8. Rectifying: Turning on or off the semi-closed conductor switch element at a predetermined time.

9. Energy storage: To store electrical energy for release when it is needed. Such as camera flash, heating equipment, etc. (Some capacitors are now close to the level of lithium-ion batteries, storing enough energy to power a mobile phone for a day.