Types of Capacitors


Introduction

There are different types of capacitors available in the present days. They each vary in their characteristics and applications. Because each have their own advantages and disadvantages. Few types of capacitors can charge up to higher voltages such as electrolytic capacitors. So they can be used in high voltage power correction and smoothing circuits. Some capacitors have very low leakage rates and others have very high leakage rates. Mainly these factors determine how and in what application a type capacitor is used.

The differences between the different types of capacitors are generally made with according to the dielectric material which is used between the metal plates. Like resistors, the capacitors are also available in different types in the present markets, which allow us to vary their capacitance value to use in frequency timing type circuits.

In general small capacitors are constructed with ceramic materials and these are sealed by dipping them in to an epoxy region. Capacitors are playing an important role in electronic and electrical circuits. Some of the various types of capacitors are given below.

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Dielectric Capacitor

Variable types of dielectric capacitors are generally available in the market. These dielectric capacitors are mainly used in transistor radios, tuning receivers and transmitters. The multi-plate air- spaced capacitors are the variable dielectric type capacitors. They contain a set of fixed plates and a set of movable plates which move in between the fixed plates.

The overall capacitance values (C) for this type of capacitors are determined according to the position of the moving metal plates with respect to the fixed metal plates. In this design when two sets of metal plates are fully meshed together then the capacitance value is generally at maximum value. High voltage type tuning capacitors have large air-gaps or spaces between the plates with relatively large break down voltages in order of kilo volts. For this reason these dielectric capacitors are very useful in tuning circuits.

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Variable Capacitor Symbols

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The symbols for the variable type and trimmer type capacitors are shown in the above figure. A variable type capacitor is a capacitor in which we can vary the capacitance value mechanically or electronically. Generally these variable types of capacitors are used in LC circuits, to set the resonance frequency. Like variable type capacitors the preset type variable capacitors are also available, they are called ‘Trimmers’. These trimmer capacitors are non- polarized and these are also very small devices in structure. The capacitance value for these capacitors is adjusted or pre-set to a particular value which is required for the application with the use of small screwdrivers and also these values are generally less or equal to the 500pF.

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Film Capacitor

Film capacitors are the most commonly used type of capacitors among all types of capacitors which have the difference in their dielectric properties. Film capacitors are the capacitors with an insulating plastic film as its dielectric and these are non-polarized capacitors. The dielectric materials for these capacitors are existed in the form of a thin layer which is provided with metallic electrodes and it is wounded in to a cylindrical winding. The both electrodes of film capacitors may be zinc or metalized aluminum.

The main advantage of film capacitor is direct connection between its internal construction and its electrodes on both ends of the winding. This direct contact with electrodes causes to keep all current paths to become short. This design behaves like a large number of individual capacitors connected in parallel. And also this type of capacitors structure results in low ohmic losses and the low parasitic inductances. These film capacitors are used in AC power applications and also used in the high frequency applications.

Some of the examples of plastic films which are used as dielectric for the film capacitors are Polypropylene, Polyethylene naphthalate, Polyester, Polyphenylene sulfide and Polytetrafluoroethylene. Film type capacitors are in the market with capacitance value ranges from 5pF to 100uF .Film Film capacitors also available in different shapes and different styles which includes:

  • Wrap & Fill (Oval and Round) type: In this type the capacitor ends are sealed with epoxy and the capacitor is wrapped in a tight plastic tape.
  • Epoxy Case (Rectangular & Round): In this type capacitors are encased in a moulded plastic shell and it is filled with epoxy.
  • Metal Hermetically Sealed (Rectangular & Round): These types of capacitors are encased in a metal tube or can, and sealed with epoxy.

In present days the above all case style capacitors are available in both the types Radial and Axial Leads. The main advantage of the plastic film capacitors is that, they operate well and good at high temperatures when compared to other paper types. These capacitors have small tolerance, high reliability and also they have very long service life. Examples of film type capacitors are cylindrical film, rectangular metalized film and foil film types. They are given below.

Axial Lead Type:
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Radial Lead Type:
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Foil Type Film Capcitors

These film types of capacitors require much thicker dielectric material in order to avoid the punctures and tears in the dielectric film. Hence these are suited for low capacitance value and large sizes.

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Film Power Capacitors

Film power capacitors are also called as Power film capacitors. The construction techniques and materials which are used for large power film capacitors are usually similar to those of the ordinary film capacitors. However these capacitors with high power ratings are used in the applications of power systems and electrical installations.

Power film capacitors are used in variety of applications. These capacitors serve as snubbing or damping capacitors when connected a resistor in series with it. These are also used in close tuned or low detuned filter circuits for filtering the harmonics and also used as pulse discharge capacitors.

Power Film Capacitor
Image Resource Link: en.wikipedia.org/wiki/Film_capacitor

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Ceramic Capacitors

Ceramic capacitors are also called as “Disc-capacitors”. Like electrolytic, these are also the mostly used type of capacitors. A ceramic capacitor is constructed with two or more alternating layers of ceramic and a metal. Here the ceramic acts as its dielectric and metal acts as its electrodes. These ceramic capacitors are non-polarized fixed type capacitors. Generally the electrical behavior of the ceramic material can be divided into two classes related to its stability. They are given and explained below.

  • Class 1: ceramic capacitors with high stability and low losses for compensating the influence of temperature in resonant circuit applications.
  • Class 2: These types of capacitors offer high volumetric efficiency for buffer by pass and coupling applications.

Ceramic types of capacitors are normally having a 3-digit number coded on their body to identify the capacitance value generally in pico-farads (pF). In that the first two digits are used to indicate the capacitors value and the third digit indicates the number of zeros to be added. For example a ceramic capacitor with the markings 153 would indicate 15 and 3 zero’s in pico-farads which is equivalent to15, 000 pF or 15nF.

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Polypropylene Capacitor

Polypropylene capacitor is one of the many varieties of film type capacitors. Polypropylene capacitors are the capacitors that have a polypropylene film as their dielectric. Polypropylene capacitors are available within the capacitance ranges from 100pf to 10µF.

The main feature of Polypropylene Capacitor is high working voltages up to 3000V. This feature makes polypropylene (pp) capacitors useful in circuits in which operating voltages are typically very high, such as power amplifiers particularly valve amplifiers, power supply circuits and TV circuits. Polypropylene capacitors are used when a better tolerance is needed than what a polyester capacitor can provide.

Polypropylene capacitors are also used in coupling and storage applications due to their high isolation resistance values. And also they have stable capacitance values for frequencies below 100 KHZ. These polypropylene capacitors are used in the applications where we need to perform the tasks of noise suppression, coupling, filtering timing, blocking, bypassing, and handling pulses.

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Polycarbonate Capacitor

Polycarbonate capacitors are the capacitors that have a polycarbonate material as its dielectric. These types of capacitors are available within the capacitance range of 100pF to 10µF and have the working voltages up to 400V DC. These polycarbonate capacitors can operate with a temperature range of -55°C to +125°C without de-rating. These capacitors have very good temperature coefficients, due to these reason polycarbonate capacitors are preferable. These capacitors are not used in the high-precision applications because of their high tolerance levels of 5% to 10%. The polycarbonate capacitors are also used for AC applications. Sometimes they are also found in switching power supplies.

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Silver Mica Capacitor

Silver Mica Capacitors are capacitors that are made from depositing a thin layer of silver on a mica material as its dielectric. The reason for the use of silver mica capacitors is that their high performances compared to any other type of capacitors.

Silver mica capacitors can be obtained with the tolerance of +/- 1%. This is much better than any other type of capacitor which is available in today’s market. The temperature co-efficient of silver mica capacitors is much better than other types of capacitors. And this value is positive and it is normally in the region of 35 to 75 ppm / C, with an average value of +50 ppm / C. Capacitance values for silver mica capacitors are normally in the range between a few pico-farads to 3300 pico -farads. Silver mica capacitors have very high levels of Q and also have small power factors. The silver mica capacitors have the voltage range between 100V to 1000V.

Silver mica capacitors are used in RF oscillators. The silver mica capacitors are not used in coupling and decoupling applications because of their high cost. Due to their size, cost and also the improvements in other types of capacitors these are not used nowadays.

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Electrolytic Capacitors

Electrolytic Capacitors are generally used in the applications where very large capacitance values are required. The electrolytic capacitors have a metallic anode covered with an oxidized layer generally used as its dielectric. Another electrode of a capacitor is a non-solid or solid electrolyte. Most of the electrolytic capacitors are polarized. These capacitors are categorized according to their dielectric material.

Mainly these are categorized in to three classes, they are given as

  • Aluminum electrolytic capacitors: Here aluminum acts as its dielectric.
  • Tantalum electrolytic capacitors: Here tantalum pent oxide acts as its dielectric.
  • Niobium electrolytic capacitors: Here niobium pent oxide acts as its dielectric.

Usually the permittivity of tantalum pent oxide is almost three times greater than the permittivity of aluminum dioxide, but this permittivity determines only the dimensions. Generally three types of electrolytes are used. They are as follows:

  • Non solid (wet or liquid): These capacitors have the conductivity nearly 10ms/cm and these are available with low cost.
  • Solid manganese oxide: These capacitors have the conductivity nearly 100ms/cm and also have high quality and stability.
  • Solid conductive polymer: These type of capacitors have conductivity approximately 10000 ms/cm and also the ESR values of <10mΩ.

Electrolytic Capacitors are generally used in direct (DC) power supply circuits. These are also used in the applications of coupling and decoupling to reduce ripple voltage, due to their large capacitance values and their small size. One of the main disadvantages of electrolytic capacitors is their low voltage ratings.

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Electrolytic Capacitor Diagram

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Aluminum Electrolytic Capacitors

Aluminum Capacitors are capacitors that are made of oxide film on aluminum foils with a strip of absorbent paper between them which is soaked in an electrolyte solution and all these design can be sealed in a can. Basically there are two types of Aluminum Electrolytic Capacitors they are plain foil type and etched foil type. Plain foil type electrolytic capacitors are mainly used as smoothening capacitors in power supply circuits while etched foil type capacitors used in coupling DC blocking and by pass circuits.

Electrolytic aluminum capacitors cover the capacitance range of 1uF to 47000uF and large tolerance of 20%. The working voltage ratings range up to 500V. These are cheaper and easily available in the market.

The capacitance value and voltage ratings are either printed in uF’s or coded by a letter followed by three digits. These three digits represent the capacitance value in pF where first two digits represent the number and the third one is the multiplier digit.

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Tantalum Electrolytic Capacitors

Tantalum Capacitors are capacitors that are made of tantalum pent oxide as its dielectric material. Tantalum electrolytic capacitors are also polarized capacitors like aluminum capacitors. Tantalum electrolytic capacitors are obtained in both the types of wet (foil) and dry (solid). The second terminal of tantalum electrolytic capacitors is smaller than the terminal of equivalent aluminum capacitors and that terminal is made with manganese dioxide.

The main advantage of Tantalum Electrolytic Capacitors over aluminum capacitors is that they are more stable, lighter and smaller. They have capacitance values range from 47nF to 470uF and maximum working voltage up to 50V.These are costlier than aluminum electrolytes.

The properties of the tantalum oxide dielectric are low leakage current and better capacitance stability. These properties of tantalum oxide dielectric cause to use them in blocking, by-passing, decoupling, filtering and timing applications. And also these properties are much better than the dielectric of aluminum oxide.

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Super Capacitors

The super- capacitor is also known as ultra-capacitor or electric double-layer capacitor. These capacitors are made with a thin electrolyte separator which is flanked with activated carbon ions. It differs from a regular capacitor, the capacitance value of a super capacitor is very high and it is in order of milli farads with the voltage ranges of 2.3V to 2.75V.

Super capacitors are categorized into three types based on their electrode design they are

  • Double-layer capacitors: These capacitors have carbon electrodes or their derivatives.
  • Pseudo capacitors: These capacitors have metal oxide or conducting polymer electrodes.
  • Hybrid capacitors: These capacitors have asymmetric electrodes.

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Super capacitors are mainly used in the applications, where very high number of charge/discharge cycles is needed, where long lifetime is required and where the large amount of power is needed within a short time. The typical applications range of super capacitors are from milliamp current and milli-watts of power with a duration of few minutes to several amps current and several kilo watts power within a shorter period. These super capacitors are generally used as temporary power source, as a replacement of batteries.

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