Research on Film Capacitor Classification

• Summary

In the audio circuit design, the film capacitor is a frequent visitor. Its loss angle is very low, its capacitance value is small, and its withstand voltage is relatively large. It can be used for coupling, filtering, decoupling, and other occasions.

In the application, I found that there are many types of thin film capacitors, and the focus of technical parameters is different from that of electrolytic capacitors. So I checked Wiki and datasheet from various manufacturers and made a summary here.

In general, the performance of the Thin Film Capacitor is good, but it is also divided into many types and levels, and the application scenarios are also different. The basic knowledge is detailed on the Wiki, showing the electrode/Dielectric Materials of thin film capacitors and their abbreviations:

• Electrode Material

The initial m Refers to the metal film electrode (a thin metal layer is made on the plastic film), and F refers to the metal foil electrode (a separate metal foil, not attached to the plastic film ).

Both fks and fkp use metal foil as the electrode. Theoretically, the loss angle and other parameters can be better done. However, the advantage of the metallic thin film electrode is that the capacitor size is smaller because the metal layer as the electrode is very thin.

The first letter represents the media material.

• Dielectric material

Currently, the most common MKT and mks capacitors are both metallic polyester (PET, commonly known as polyester) film capacitors.

The famous mkp is a metal polypropylene (PP) capacitor.

In addition, the fkc/MKC poly acetate (PC) capacitor, although most manufacturers have stopped production, but the inventory can also be seen, the performance is also good. The main reason for the shutdown is that PC films are no longer produced since 1990s.

Teflon capacitors are also available in some of the top-level audio coupling capacitors.

Polystyrene (PS) capacitors are common in CBB capacitors. Metal polypropylene (PPS) is mostly used for SMD film capacitors. Polyethylene naphtha capacitor pen has not been seen yet.

• Stability

The more important information is the temperature and frequency stability.

PET has poor temperature and frequency stability.

Without considering the frequency stability, PPS is the best in terms of temperature stability.

Frequency/TemperatureIn combination, PP is the best.

In addition, although the fkc/MKC capacitor has basically been discontinued, I found that when studying the fkc capacitor,The temperature stability of PC materials is also very good, or even exceeds PPAccording to WIMA:

 

Compared with PET and PP, PC is more stable in terms of electrical capacity stability, especially in the range of 0-80 degrees.

In addition, the frequency of the PC is also good:

 

The loss angle is about 10, 20,-4 at a frequency of 1 K, 10 K, and kHz, which is slightly worse than that of PP. The overall performance is similar to that of PPS. It can be used in high-frequency applications.

• Application

For the capacitors of different brands, the performance is mainly determined by materials, which has little to do with the brands.From the perspective of the loss angle, even the best pet has an order of magnitude gap with the worst pp..

The main advantage of PET capacitance is that it is cheap. Most of the prices are about half of the same type of PP, And the size is smaller than that of PP. It is suitable for power supply (energy storage), direct separation, decoupling, bypass, and other applications.

The PP capacitor is expensive, and the high-frequency performance is very good. It can be stringed in the signal path to play a coupling effect.

PC capacitors are currently scarce, mainly in stock. The stability is very good, and the high-frequency performance is good. It can be used in applications with high precision requirements such as filters.

However, the performance difference between the metallic film and the metal foil electrode is very small. The metallic film has an advantage in volume and can be used preferentially in applications.

Research on Film Capacitor Classification