Film Capacitors

Film capacitor (Film Capacitor(Metal Oxide Varistor)) is also known as plastic film capacitor (Plastic Film Capacitor). To the plastic film as a dielectric.

Description:

The capacitor according to different media, many of its kind, for example: electrolytic capacitors, paper capacitors, film capacitors, ceramic capacitors, mica capacitors, air capacitance. But the most frequently used in audio equipment, undoubtedly electrolytic capacitors and film capacitors (Film). Most of the electrolytic capacitors are used in a lot of places that need power capacity, for example, the main power supply filter capacitor part, in addition to filtering, and also cater to store electrical energy. While the film capacitors are widely used in the bypass to the cross-connected, power supply noise of the analog signal (anti-cross-linked) and other places.

Structure and classification:

The film capacitor When the electrode based on a metal foil, and polyethylene ethyl acrylate, polypropylene, poly stupid plastic film such as vinyl or a polycarbonate, from the overlap of the ends, wound into a cylindrical structure of a capacitor. Accordance with the type of plastic film and are respectively known as poly ethyl capacitance (also known as Mylar capacitor), polypropylene (also known as PP capacitors), polystyrene capacitance the (called PS capacitor) and poly carbonate capacitance.

A typical schematic diagram on the film capacitor.

Features:

Film capacitors has many excellent features, it is an excellent performance of the capacitor. Reciprocity as follows: polarity, insulation resistance is high, excellent frequency characteristics (wide frequency response), and the dielectric loss is very small. Based on the above advantages, the thin film capacitor is large-scale use in the analog circuitry. Especially in the part of the signal cross-connection, you must use good frequency characteristics, low dielectric loss capacitor in order to ensure that the signal transmission, without too much distortion occurs.

Its structure and the same paper dielectric capacitors, the medium is such as polyester or polystyrene. Polyester film capacitors, high dielectric constant, small size, large capacity, better stability, suitable as a bypass capacitor. Polystyrene film capacitors, dielectric loss, high insulation resistance, temperature coefficient, can be used for high-frequency circuits.

Among all of the plastic film capacitor, the capacitance characteristics of polypropylene (PP) capacitor and polystyrene (PS) is most significant, of course, both the price of the capacitor is also relatively high. Audio equipment in recent years, however, in order to enhance the sound quality of the parts and materials used has become more and more advanced, the price is not the most important factor, so in recent years, PP capacitors and PS capacitors are used in the frequency and quantity of audio equipment Yulai higher. Readers can often see a certain brand of equipment, known how much a certain brand-name PP quality capacitor or PS quality capacitors, as the sound quality endorsement truth in this.

Feature Summary: capacity range of film capacitors for 3pF-0.1uF, DC working voltage of 63-500V, suitable for high-frequency, low frequency, leakage resistance is greater than 10,000 Ω.

Edit this paragraph metalized film capacitors

Usually a thin film capacitor of its production method is wound together made of a metal such as aluminum foil as an electrode and a plastic film overlap. But another film capacitors and have a manufacturing method, called metallized film (Metallized Film), its production method is to vacuum deposition on a thin layer of metal on a plastic film as an electrode. So omit the foil thickness of the electrode, reduced the volume of the capacity of the capacitor unit, and so the film capacitor is more easily made compact, large capacity capacitor. Common MKP capacitors, metallized polypropylene film capacitors (Metailized Polypropylene Film Capacitor) on behalf of said MKT Metallized Polyester capacitor (Metailized Polyester) said on behalf of(Metal Oxide Varistor).

The metallized film capacitor using a film polyethylene ethyl acrylate, polypropylene, polycarbonate, etc., in addition to the wound-type, there are also stacked type. This type of metalized film capacitors has a so-called I recover the role (Self Healing Action), which assumes a tiny part of the fragile quality of electricity sector and cause a short circuit, caused by a short circuit around the electrode metal part of the electrode, or short-circuit current due to the electrostatic energy of the capacitor brought, and lead to the dissolution of the larger area integration evaporated to recover the insulation, the capacitor again returning to the role of the capacitor.

Metallized film capacitor features:

Metallized film capacitor that is in the surface of the polyester film of the vapor-deposited layer of metal film instead of the metal foil as the electrode, because the thickness of the metal film layer is much smaller than the thickness of the metal foil, so the wound volume than the metal foil capacitance is much smaller. The biggest advantage of metalized film capacitors is a "self-healing" features. The so-called self-healing properties is if the thin film dielectric because at some point in the presence of defects, and in the over-voltage under the action of a short-circuit breakdown, and the breakdown point metal layer may be in the arc under the action of an instant melting evaporated forming a small non-metallic area , the capacitance of the two pole pieces are re-insulated from each other and can continue to work, thus greatly improving the reliability of the work of the capacitor. Analysis principle, metalized film capacitors should not short-circuit failure mode, and metal foil capacitor there will be a lot of short-circuit failure phenomenon. Although the metal film capacitors great advantages as described above, but compared with the metal foil capacitor, there are the following two disadvantages:

First, the capacity stability than a foil type capacitor, which is due to the metallized capacitor in the long working conditions prone capacity loss and after healing may lead to reduced capacity, therefore, as an oscillation circuit with the capacity stability demanding. should be used in the metal foil capacitor better.

Another major drawback to withstand a large current capacity is poor, which is weaker a lot due to the metalized film layer to be thinner than the metal foils, the ability to carry large currents. To improve this shortcoming of the metallized film capacitors, metalized film capacitors in high-current products in the manufacturing process has been improved, the major improvements in ways 1) to do double-sided metallized film electrode; 2) increase the metallization layer thickness; 3) the end face of the metal welding process improvements to reduce the contact resistance.

  

Edit the market segment of the film capacitor application status(Metal Oxide Varistor)

Film capacitors used in electronics, household appliances, telecommunications, electric power, railway electrification, hybrid cars, wind power, solar power and other industries, the stable development of these industries, and promote the growth of the thin film capacitor market.

With the technical level of development, electronics, home appliances, communications and other industries replacement cycles are getting shorter, and thin-film capacitors with good electrical performance and high reliability electronic components promote these industries are upgrading an integral [1]. With digital, information technology, network construction further development and national increase in power grid construction, the electrified railway construction, energy-efficient lighting, hybrid cars and other inputs as well as consumer electronics products in the next few years to upgrade, film capacitor market demand further presents the trend of rapid growth.

According to the China Electronic Components Industry Association statistics, it is expected that in 2010, the global film capacitor market will be 15 to 20% of the speed of rapid growth, film capacitor market growth will drive the rapid growth of the market of polypropylene electronic film(Metal Oxide Varistor).