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What are the Film Capacitor and Its Application?

Author: Apogeeweb Date: 12 Jan 2021  344

Features and Applications of Film Capacitors

Ⅰ Introduction

One of those imperative passive electrical components that are present in a large range of circuits is capacitors. If you are a DIY enthusiast who is enthusiastic about electronic circuits, it is a must to understand the condenser types to use them correctly in suitable circuits. We help you decode and understand the uses of one of the most common types of capacitors are called the film capacitors here in this article. The fundamentals of capacitors, their forms and when to use them, have already been discussed. Notice that Film Capacitors are known by several names, Polyester Capacitors and Mylar Capacitor are some common ones, all of them, in general, are covered in this article.

 

Capacitors can generally be divided into two broad categories: polarized and nonpolarized. Due to its flexibility and low cost, the film capacitor is a form of non-polarized capacitor and is very common. Read on to learn more about a film condenser: what a film condenser is, how it is made, and what makes it so famous. Let's start with this little passive gadget with a brief introduction.

Catalog

Ⅰ Introduction

Ⅱ Definition of Film Capacitors

Ⅲ A Variety of Capacitors

Ⅳ Brief History of Film Capacitors

Ⅴ Types of Film Capacitors and Their Applications

  5.1 Film/Foil Capacitors

  5.2 Metalized Film Capacitors

Ⅵ Features and Applications of Film Capacitors

Ⅶ How is Film Capacitor different from Electrolytic Capacitor and Ceramic Capacitor?

Ⅷ Construction of Film Capacitor

Ⅸ FAQ

Ⅱ Definition of Film Capacitors

The film capacitor is a non-polarized capacitor and thin plastic films are used to produce its dielectric. These plastic films are often metalized and are available under the name of 'metalized condenser' on the market. Such capacitors are also often referred to as plastic capacitors or metalized capacitors. A Thin Film Capacitor is nothing but a plastic film with bipolar capacitors as their dielectric. To form a roll or a candy-like rectangular shape, these films are either metalized or just put in layers. Polypropylene(PP) /Polyethylene terephthalate (PET)/ Polytetrafluoroethylene(PTFE)/Polyphenylene Sulfide (PET) are the dielectrics widely used (PPS)

 

The primary benefit of using a film capacitor is that it has a very low distortion factor and excellent frequency features. The wide variety of plastic film used for various film condensers makes them flexible. These capacitors often do not wear off easily and are ideal for applications such as coupling/decoupling circuits, ADC, audio circuits, and many more for high voltage and high-frequency applications. Bypass and decoupling capacitors, which are popular applications for condensers, have also been addressed previously.

Ⅲ A Variety of Capacitors

We need to understand the context behind the common words Film Capacitor, Polyester Capacitor, Mylar Capacitor, and Polypropylene Capacitor before we continue with our post. There are several types of film capacitors depending on the type of dielectric plastic material used in the capacitor, one of which is the most widely used polyester condenser and polypropylene condenser.

 

Often known as Polyester Film Capacitors, the polyester capacitor has a dielectric material made of a polymer named polyethylene terephthalate (PET). This is why often this capacitor is referred to as the PET Film Capacitor. There are several Polyester Capacitor manufacturers, of which Hostaphan is the leading one. The Polyester Capacitor is also often called a Mylar Capacitor to address the vendor term. Below, a typical Mylar capacitor is shown.

Polyester-Film-Capacitor

Another type of film capacitor in which the dielectric material is made of polymer caller polypropylene (PP), is the polypropylene film capacitor, hence the name Polypropylene Film Capacitor or PP Film Capacitor. Below is a typical polypropylene capacitor.

polypropylene capacitor

Similarly, depending on the type of polymer used for the dielectric, there are more than 10 different types of film capacitors, the properties of which vary slightly, but the overall functionality and application almost remain the same. We will get into the specifics later, but let's dive into history before that.

Ⅳ Brief History of Film Capacitors

Paper capacitors were used in the decoupling circuits before film capacitors came into the picture. Impregnated paper that was placed with metal strips and rolled into cylindrical forms was used by paper condensers. Since these capacitors had paper as a dielectric, however, they were not only likely to be vulnerable to environmental defects and were very voluminous in size. Scientists have therefore started to look for a solution that would mitigate these problems.

 

It was at a time when the plastic industry was booming and scientists discovered how long-term stability in terms of its electrical parameters was given by the use of complex plastic films as a dielectric. As multilayers of paper were replaced by only a few sheets of plastic, it also helped to reduce the bulk. As technology progressed, thinner plastics with high reliability decreased the size of these capacitors.

Ⅴ Types of Film Capacitors and Their Applications

The plastic industry saw growth in the production of thinner and more robust goods soon after the first film capacitor was introduced. Different kinds of plastic film capacitors have been used as a dielectric to accommodate various circuit applications over the years. There are several film condensers in which the plastic films are actually put between the aluminum foils and there are others in which the plastic film is metalized by a phase in which the metal is coated on the film itself. In general, based on construction, film capacitors can be divided narrowly into two groups. Notice that only the construction is based on the classification.

5.1 Film/Foil Capacitors

The film/foil capacitor, as the name implies, uses plastic films as a dielectric and is mounted within two layers of aluminum foil electrodes. These interleaved layers are so organized that they do not touch each other with the metallic layers. Such capacitors can be either non-inductive or inductive.

Foil Capacitors

In such a way that the aluminum foils are located in the middle of the two films, an inductive film foil capacitor is wound. The aluminum foils are not directly attached but through a leading wire that carries the entire winding. A pictorial representation of it is shown in Figure 1.

Inductive-Film-Foil-Capacitor

In a non-inductive fill foil capacitor, the aluminum foils are arranged in such a way that each foil is positioned to a certain degree out of the films, such as that shown in Figure 2.

Non-Inductive-Film-Foil-Capacitor

Plastic Film Capacitor Characteristics:

• High insulation resistance

• Good capacitance stability

• High efficiency even at high frequency

• Dielectric used: Polypropelene(PP)/ Polyethylene terephthalate (PET)/Polytetrafluoroethylene(PTFE)

Plastic Film Capacitor Application

The film/foil capacitor application depends on the type of dielectric used. For coupling, decoupling, and bypassing, PET Film/foil capacitors are great. PP Film/Foil (PP) capacitors are a good choice for use in circuits requiring high switching frequencies, such as resonant and oscillator circuits, power supplies, etc.

5.2 Metalized Film Capacitors

The primary distinction between a film foil capacitor and a metalized capacitor is that the metallic electrodes are fused into either side of the dielectric plastic in the latter instead of layering. While it raises the cost and also adds a step in the production process, it has greater reliability and smaller dimensions than in a film foil condenser. To get the desired capacitance value, the thickness of the plastic film can be as low as 0.6μm.

Metalized film capacitors

Metalized Film Capacitor Characteristics:

• Self-healing property: This property helps the capacitor to repair itself if the electrodes are exposed to each other instead of being short-circuited. This increases the capacitor reliability

• Compact in dimension and form

• Polypropylene(PP)/polyethylene terephthalate(PET)/ polytetrafluoroethylene(PTFE)/ polyphenylene sulfide Dielectric used: polypropylene(PP)/polyethylene terephthalate (PET) (PPS)

Metalized Film Capacitor Application:

In electronic control circuits, including DC link circuits, pulse circuits, switching circuits, etc., metallic film capacitors are commonly used.  In decoupling and filtering applications, the low power metalized film capacitor finds use.

Ⅵ Features and Applications of Film Capacitors

The film capacitors often provide other features, in addition to the normal use of condensers to accumulate electrical charges. In high-frequency circuits, their bipolar nature and exceptional frequency characteristics make them famous. The standard capacitance value for these capacitors, in general, ranges from 1nF to 30muF. These small passive parts can have a voltage level of as low as 50 V and as high as 2 kV, so they can be used in a wide variety of applications.

 

One of the fascinating facts is that various types of plastic film are used by these film capacitors as a dielectric. In general, each type of film provides a condenser with different temperature and frequency characteristics. Therefore, one can select the best solution for their needs in their circuits with the correct choice of the dielectric. For example, the PP film capacitor would be the best choice if you are looking for a film capacitor to be mounted in a circuit intended for high-power/high-frequency applications, such as induction heaters, for example.

 

A comparison of the frequency and temperature characteristics of 4 different plastic film dielectrics, namely PP, PPS, PEN, and PET, is shown in the figure below. The only difference is the dielectric material between these capacitors and you will note the shift in temperature and frequency is very obvious.

Plastic-Film-Dielectric-Characteristics

Among other aspects, film capacitors are mainly known for their low dissipation factor, stable capacitance, and high insulation resistance, such as negative temperature and high-reliability characteristics. Hence, for a wide range of applications, they are common choices. These film capacitors generate optimum output from simple sample/hold circuits for ADCs, oscillatory circuits, timers, to finding a position in the coupling/decoupling units of high-end electronic power circuits.

 

Over the past few decades, these capacitors have replaced the use of ceramic and electrolyte capacitors in many circuits in automotive and industrial applications. For some applications, let's compare the film capacitor with the other common capacitors and get to know what makes them a better option.

Ⅶ How is Film Capacitor different from Electrolytic Capacitor and Ceramic Capacitor?

The first difference between these three capacitors that is quite obvious is the type of dielectric used and their construction. While film capacitors use thin sheets of plastic film, ceramic capacitors, like the dielectric, use sheets made of ceramic material. In nature, both of them are bipolar. On the other hand, electrolytic capacitors have oxides that act as dielectrics and are polar.

 

The differences in their production and dielectrics have an enormous impact on their results. As discussed above, a wide variety of capacitance values are available for plastic film/metalized film capacitors. Ceramic capacitors, on the other hand, are only ideal for circuits that have low requirements for capacitance. For specific applications such as analog signal processing and audio circuits, due to the low distortion factor they offer, film capacitors are preferred over ceramic capacitors. Ceramic capacitors also tend to have high nonlinearities at high capacitances that affect the performance of the circuits.

 

Capacitors with high capacitance and a low cost are favored for applications such as coupling/decoupling circuits. Both electrolytic and film capacitors are also good choices to choose from. The ESR (Equivalent Series Resistance) and ESL (Equivalent Series Inductance) value of the capacitor is another major factor that is considered when designing such circuits. As already discussed, in contrast to electrolytic capacitors, film capacitors have a stronger ESR and ESL performance and a much lower distortion factor and are thus favored over aluminum electrolytic capacitors.

 

Also, if the aging time between these three capacitors is compared, film capacitors appear to avoid the wearing out process between them for the longest time. For high voltage and high-frequency applications, this makes them a safer option.

Ⅷ Construction of Film Capacitor

The generic method of development for these capacitors begins with the removal of a thin layer of plastic film. This film's thickness determines the capacitance value. Since the capacitance value increases with a decrease in the gap between the electrodes, the higher capacitance value is thus indicated by the lower film thickness. The standard capacitance value for these capacitors, in general, ranges from 1nF to 30muF.

 

Once the film is removed according to the desired capacitance value and the breakdown voltage, either aluminum or zinc is metalized and rolled over to form a' mother roll.' The films are only interlaced between sheets of aluminum foil to form the roll in the case of a film/foil capacitor. A flow diagram of the different steps involved in producing a metalized film capacitor is shown in the figure below.

Capacitor-Manufacturing-Process

This roll is then manipulated to accommodate the capacitor size and the desired electrical characteristics by several processes such as slitting, winding and flattening. The projecting electrodes are subjected to a metalizing process called 'Schoopage' until the capacitor obtains its desired shape and size. To create a protective coating on the electrodes, liquefied metals such as zinc, aluminum, or tin are used here. To burn away any existing defects on the electrode surface, the lateral ends of the winding are then sprayed with compressed air and then exposed to a voltage.

 

Since the capacitors can be easily influenced by moisture, silicone oil, or some other insulating fluid is impregnated with the winding. Finally, this winding is prepared to be soldered to the capacitor's metallic terminals. The capacitor is subjected to a final round of protection coating until soldered, where its body is dipped into a protected coating or potted on the outer casing.

Ⅸ FAQ

1. What is a film capacitor?

A film capacitor is a plastic capacitor that is used to construct the dielectric and aluminum or zinc is used to construct the electrodes of the capacitor.

 

2. Can film capacitors explode when overloaded (like electrolytic)?

If the overvoltage is very large you can damage them, eventually burn them, as with any electronic component you abuse. But IMHO explosion of film capacitors is not very likely. The danger when dealing with liquid electrolytic capacitors is that the electrolyte is acid, and if they explode they can cause severe injuries, for instance in the eyes.

 

When they are 'abused' with over-voltage or with high reverse voltage (they are polarized, remember…) the pressure inside increases and they eventually explode. To avoid the pressure increases too much, they have 'escape valves' in the same way as high-pressure kitchen boilers have. In the capacitors those escape valves are thin 'weakened spots' in the plastic cover or there are cross-shaped grooves in the aluminum. 

 

3. What is a film capacitor used for?

Film capacitors can also be used in a more conventional way as voltage smoothing capacitors, filters, audio crossovers. They can be used to store energy and release it in a high-current pulse when needed. High-current electrical pulses are used to power pulsed lasers or generate lightning discharges.

 

4. What is the preferred application of a film capacitor?

For particular applications like analog signal processing and audio circuits, film capacitors are preferred over ceramic capacitors due to the low distortion factor which they offer. Also at high capacitances, ceramic capacitors tend to have high nonlinearities which affect the performance of the circuits.

 

5. How do you determine the polarity of a film capacitor?

Based on the height of the capacitor leads we can identify which is negative polarity and which is positive polarity. Capacitor whose terminal is longer is a positive polarity terminal or an anode and the capacitor whose terminal is shorter is a negative polarity or cathode.

 

6. What is an electrolytic or film capacitor?

While the active part of electrolytic capacitors, the so-called wound cell, consists of aluminum (anode and cathode foil), paper, and electrolyte, the film capacitor is made of metal-coated plastic film that builds its electrodes.

 

7. Can I replace the film capacitor with ceramic?

Yes, they are interchangeable, but ceramic disc capacitors are considerably more nonlinear in their voltage and frequency response compared to film capacitors. Ceramic caps can also be microphonic.

 

8. How do you use a film capacitor?

Most power capacitors, the largest capacitors made, generally use polypropylene film as the dielectric. PP film capacitors are used for high-frequency high-power applications such as induction heating, pulsed power energy discharge applications, and AC capacitors for electrical distribution.

 

9. How long do film capacitors last?

The MKP1848 film capacitor has a life quoted as 100000 hrs at 70 degC. The life of a Rubycon BXC series wet electrolytic capacitor is quoted as 12000 hrs at 105degC. By way of the '10 degree rule', we can say that the lifetime of the Rubycon electrolytic capacitor at 70 degC would be 96000 hrs.

 

10. Do film capacitors degrade?

The degradation of metalized film capacitors is a concern in applications exposed to high humidity environments. The metalized electrode layer in metalized film capacitors is very thin, typically less than 50 nm, which is susceptible to corrosion due to the ingress of atmospheric moisture.

Ordering & Quality

Photo Mfr. Part # Company Description Package PDF Qty Pricing
(USD)
T491B476K010AT T491B476K010AT Company:KEMET Remark:Tantalum Capacitors - Solid SMD 10V 47UF 1311 10% ESR=1 Ohms Package:N/A
N/A
In Stock:On Order
Inquiry
Price:
1+: $0.57000
10+: $0.31300
100+: $0.22000
500+: $0.20200
1000+: $0.17200
2000+: $0.13700
10000+: $0.13300
24000+: $0.12900
50000+: $0.12500
Inquiry
T491X476K035AT T491X476K035AT Company:KEMET Remark:Tantalum Capacitors - Solid SMD 35V 47uF 2917 10% ESR=600mOhms Package:N/A
N/A
In Stock:On Order
Inquiry
Price:
1+: $2.65000
10+: $2.05000
100+: $1.62000
500+: $1.08000
1000+: $0.96900
2500+: $0.90000
10000+: $0.86500
Inquiry
C0603X104K5RACTU C0603X104K5RACTU Company:KEMET Remark:Multilayer Ceramic Capacitors MLCC - SMD/SMT 50V 0.1uF 0603 X7R 0.1 Package:N/A
N/A
In Stock:On Order
Inquiry
Price:
1+: $0.19000
10+: $0.07700
100+: $0.06500
500+: $0.04400
1000+: $0.03900
4000+: $0.03300
8000+: $0.02900
24000+: $0.02800
48000+: $0.02700
Inquiry
EEU-FC1J101 EEU-FC1J101 Company:Panasonic Remark:Aluminum Electrolytic Capacitors - Radial Leaded 100uF 63V Package:N/A
N/A
In Stock:On Order
Inquiry
Price:
1+: $0.51000
10+: $0.39000
2500+: $0.13200
Inquiry

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