Film capacitors

A film capacitor consists of two conductive metal layers that are insulated from each other by a thin insulating layer made of a plastic film. The metal layers serve as electrodes and the insulating layer as a dielectric.

A film capacitor is constructed by placing the plastic film between the two metal layers. The metal layers are folded around the edges of the plastic film in order to mechanically stabilize the capacitor and establish the electrical connection.

The way a film capacitor works is based on the principle of electrostatic charging. When a voltage is applied to the electrodes, an electric field is created between the metal layers. The electric current cannot flow through the insulating layer, so the charge accumulates on the electrodes.

The capacitance of a film capacitor depends on the surface area of the electrodes, the distance between the electrodes and the dielectric constant of the dielectric. The larger the surface area of the electrodes and the smaller the distance between them, the greater the capacitance of the capacitor.

Film capacitors are often used in various electronic applications as they offer high capacitance and good electrical properties. They are particularly suitable for applications that require high accuracy and stability, such as in high-frequency circuits, filters or interference suppression capacitors.

There are various types of film capacitors, which differ mainly in terms of material, structure and area of application. Here are some of the most common types:

1. polyester capacitors (also called mylar capacitors): These capacitors are made of polyester films and are used for low voltage applications, such as in audio amplifiers, electronic circuits and DC suppression.

2. polypropylene capacitors: They are made of polypropylene films and are used in high frequency applications, high current circuits and audio applications due to their high stability and low losses.

3. polycarbonate capacitors: They are made of polycarbonate films and are used for applications with high quality and precision, such as oscillators, filters and measurement technology.

4. polytetrafluoroethylene (PTFE) capacitors: These capacitors are made from PTFE films and are characterized by their high temperature resistance and insulating properties. They are used in high-frequency and high-temperature applications such as satellite communications, aerospace, medical devices, etc.

5. metallized polyester capacitors: These capacitors are made of polyester films with a metal coating and are used in electronic devices such as televisions, computers, fluorescent lamps and energy-saving lamps.

6. metallized polypropylene capacitors: Similar to metallized polyester capacitors, these capacitors are made of polypropylene film with a metal coating. They are used in high voltage applications such as switching power supplies and motor applications.

This list is not exhaustive, as there are other types of film capacitors. The choice of the right type of capacitor depends on the specific requirements of the application, such as voltage, current, frequency range, ambient temperature, etc.

The performance of a film capacitor is influenced by various parameters, including

1. capacitance: The capacitance of a capacitor indicates how much charge it can store. The higher the capacitance, the more charge the capacitor can store and the more powerful it is.

2. dielectric strength: The dielectric strength of a capacitor indicates how much voltage it can withstand before it is destroyed. The higher the dielectric strength, the more powerful the capacitor.

3. dissipation factor: The dissipation factor of a capacitor indicates how much energy is lost during the charging and discharging process. A low dissipation factor means a more efficient performance of the capacitor.

4. temperature stability: The temperature stability of a capacitor indicates how well it retains its properties at different temperatures. A capacitor with good temperature stability maintains its performance even at extreme temperatures.

5. frequency dependence: Some capacitors can reduce their capacitance at high frequencies. The frequency dependence indicates how well the capacitor maintains its capacitance at different frequencies.

6. size: The size of a capacitor can also affect its performance. Smaller capacitors often have lower capacitance and dielectric strength, while larger capacitors can be more efficient.

Film capacitors have different properties and applications in high-frequency and low-frequency technology due to their design features and electrical properties.

In high-frequency technology, film capacitors are preferred due to their low losses and high stability at high frequencies. They have low series inductance and series resistance, resulting in low losses and better performance at high frequencies. Film capacitors can also handle high voltages and high capacitances in high-frequency technology.

Film capacitors are preferred in low-frequency technology due to their high reliability and long service life. They have high insulation strength and low ageing, resulting in stable performance over a long period of time. Film capacitors also have low self-inductance and are therefore well suited for low-frequency applications.

Applications of film capacitors in high-frequency technology include filters, oscillators, resonant circuits and RF amplifiers. In low-frequency technology, film capacitors are used in power supplies, audio amplifiers, low-frequency circuits and other applications where high stability and reliability are required.