Capacitor MarkingsCapacitors are often marked with codes to show the value, tolerance and material. This is particularly true for small types such as ceramic disc or polystyrene where there is little space for full markings.

Value Codes:

The capacitance value is often marked using a 3 digit code. This works in the same way as resistor coding but using numbers instead of colours. The first 2 numbers give the value and the last number is the multiplier. These give the value in Picofarads (pF), e.g. code 103 = 1 0 000pF (=0.01uF - see Capacitance Conversion Table). Alternatively the value may be marked directly, for example 2n2 is 2.2 Nanofarads (nF).

Tolerance Code:

A single letter is often used to indicate the tolerance of the component. These can be translated using the following table:

Tolerance Code Tolerance

C +/- 0.25pF

D +/- 0.5pF

F +/- 1%

G +/- 2%

J +/- 5%

K +/- 10%

M +/- 20%

Z - 20% +80%

Material Code:

The dielectric material is often marked in abbreviated form. The table below shows the meaning of these abbreviations.

Marking Material

MKT Metallised Polyester (PETP)

MKC Metallised Polycarbonate

KT Polyester Film / Foil

KS Polystyrene Film / Foil

KP Polypropylene Film / Foil

MKP Metallised Polypropylene

Capacitor types- an overview, information or tutorial about the different capacitor types looking at different types of capacitor and their construction, specifications and parameters.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

Electronic capacitors are one of the most widely used electronic components. These electronic capacitors only allow alternating or changing signals to pass through them, and as a result they find applications in many different areas of electronic circuit design. There are a wide variety of types of capacitor including electrolytic, ceramic, tantalum, plastic, sliver mica, and many more. Each capacitor type has its own advantages and disadvantages can be used in different applications.

The choice of the correct capacitor type can have a major impact on any circuit. The differences between the different types of capacitor can mean that the circuit may not work correctly if the correct type of capacitor is not used. Accordingly a summary of the different types of capacitor is given below, and further descriptions of a variety of capacitor types can

be reached through the related articles menu on the left hand side of the page below the main menu.

Capacitor construction

In essence the construction of an electronic capacitor is very simple, although in practice a lot of research and development has been put into capacitor technology. The basic electronics components consist of two plates that are insulated from one another. In between them there is an insulating medium known as the dielectric. The value of the electronic capacitor is dependent upon the area of the plates, the distance between them and the dielectric constant of the material or dielectric between them. The greater the area of the plates, the closer they are together and the greater the value of the dielectric constant the greater the value of capacitance.

Today, electronic capacitors are able to provide relatively high levels of capacitance within components that occupy a small volume. This is achieved in a number of ways. One is to have several sets of plates, and another is to place the plates very close to one another, having a thin layer of dielectric placed between them. In addition to this special insulating dielectric materials have been developed to enable high levels of capacitance to be achieved.

The method of construction of these electronic components is also important. In some capacitors the plates may be flat, and normally these capacitors will have rectangular, or more exactly cuboid shapes. Some will be tubular and in these capacitors the plates will be wound round on each other. The reasons for these types of construction are normally dependent upon the way in which the capacitors must be manufactured. The final stage in the construction of an electronic capacitor is to place it in a protective casing. In some instances it may be dipped in an insulating coating, in others it may be contained within a metal can.

Some capacitors types are what are termed polar or polarised. When this is the case the electronic capacitor has a positive and a negative connection and it must be placed in circuit so that the voltage across it is in a particular sense. If the voltage is incorrectly placed across the component then it may be damaged. Fortunately many capacitors, and in particular low value ones are non-polar and can be placed in circuit either way round.

Although there is a large variety that are available the most commonly used are ceramic, plastic film types, electrolytic and tantalum. These names refer to the type of dielectric that is used within the capacitor.

Ceramic capacitor

Ceramic capacitors are normally used for radio frequency and some audio applications. Ceramic capacitors range in value from figures as low as a few picofarads to around 0.1 microfarads. In view of their wide range and suitability for RF applications they are used for coupling and decoupling applications in particular. Here these ceramic capacitors are by far

the most commonly used type being cheap and reliable and their loss factor is particularly low although this is dependent on the exact dielectric in use. Their stability and tolerance is not nearly as good as silver mica types, but their cost is much less. In view of their constructional properties, these capacitors are widely used both in leaded and surface mount formats.

There are a number of dielectrics that can be used with ceramic capacitors. For low values a dielectric designated "C0G" is normally used. This has the lowest dielectric constant but gives the highest stability and lowest loss. Where higher values are required in a given size, a dielectric with a higher dielectric constant must be used. Types with designations X7R and for higher values, Z5U are used, however their stability and loss are not as good as the capacitors made with C0G dielectric. Read more about the ceramic capacitor

Electrolytic capacitor

Electrolytic capacitors are the most popular type for values greater than about 1 microfarad. Electrolytic capacitors are constructed using a thin film of oxide on an aluminium foil. An electrolyte is used to make contact with the other plate. The two plates are wound around on one another and then placed into a can that is often aluminium.

Electrolytic capacitors are polarised, and care should be taken to ensure they are placed in circuit the correct way round. If they are connected incorrectly they can be damaged, and in some extreme instances they can explode.

Electrolytic capacitors have a wide tolerance. Typically the value of the component may be stated with a tolerance of -50% +100%. Despite this they are widely used in audio applications as coupling capacitors, and in smoothing applications for power supplies.

Electrolytic capacitors are available in both leaded and surface mount formats. The surface mount electrolytic capacitors are available in rectangular packages whereas the leaded versions are normally contained in a tubular aluminium can, each end being marked to show its polarity. Read more about the electrolytic capacitor

Tantalum capacitor

Ordinary aluminium electrolytic capacitors are rather large for many uses. In applications where size is of importance tantalum capacitors may be used. These are much smaller than the aluminium electrolytic capacitors and instead of using a film of oxide on aluminium they us a film of oxide on tantalum. Tantalum capacitors do not normally have high working voltages, 35V is normally the maximum, and some even have values of only a volt or so.

Like electrolytic capacitors, tantalum capacitors are also polarised and they are very intolerant of being reverse biased, often exploding when placed under stress. However their small size makes them very attractive for many applications. They are available in both leaded and surface mount formats. Read more about the tantalum capacitor

Silver Mica Capacitor

Silver mica capacitors are not as widely used these days as they used to be. However these electronic components can still be obtained and are used where stability of value is of the utmost importance and where low loss is required. In view of this one of their

major uses is within the tuned elements of circuits like oscillators, or within filters.

Values are normally in the range between a few picofarads up to two or possibly three thousand picofarads.

For this type of capacitor the silver electrodes are plated directly on to the mica dielectric. Again several layers are used to achieve the required capacitance. Wires for the connections are added and then the whole assembly is encapsulated. Read more about the silver mica capacitor

Polystyrene Film Capacitor

Polystyrene capacitors are a relatively cheap form of capacitor. They are tubular in shape resulting from the fact that the plate / dielectric sandwich is rolled together. This adds some inductance and means that they are only suitable for relatively low frequency circuits, typically up to a few hundred kHz. In view of their relatively good tolerance levels they can be used in filter circuits, etc where values are of importance. They are generally only available as leaded electronics components.

Polyester Film Capacitor

Polyester film capacitors are used where cost is a consideration as they do not offer a high tolerance. Many polyester film capacitors have a tolerance of 5% or 10%, which is adequate for many applications. They are generally only available as leaded electronics components.

Metallised Polyester Film Capacitor

This type of capacitor is a essentially a form of polyester film capacitor where the polyester films themselves are metallised. The advantage of using this process is that because their

electrodes are thin, the overall capacitor can be contained within a relatively small package. The metallised polyester film capacitors are generally only available as leaded electronics components.

Polycarbonate capacitor

Polycarbonate capacitors have earned a place as a reliable form of capacitor for use in a number of applications where performance is critical. The polycarbonate film is very stable and this enables high tolerance capacitors to be made which will hold their capacitance value over time. In addition they have a low dissipation factor, and they remain stable over a wide temperature range, many being specified from -55C to +125C.

In 2000 the Bauer Corporation announced they would be ceasing manufacture of the raw dielectric. As a result many of the manufacturers of polycarbonate ceased production. Fortunately there are a few smaller manufacturers of these capacitors, so they can still be obtained. Read more about the polycarbonate capacitor

Polypropylene Capacitor

The polypropylene is sometimes used when a higher tolerance is necessary than polyester capacitors offer. As the name implies, this capacitor uses a polypropylene film for the dielectric. One of the advantages of the capacitor is that there is very little change of capacitance with time and voltage applied. They are also used for low frequencies, with 100 kHz or so being the upper limit. They are generally only available as leaded electronics components.

Summary of capacitor types

The table below gives and overview of the main characteristics of the various types of capacitor.

Capacitor types

Capacitance range

AccuracyTemperature

stabilityLeakage Comments & details

Electrolytic 0.1 µF - ~1 F V poor V poor Poor

Polarised capacitor - widely used in power supplies for smoothing, and bypass where accuracy, etc is not required.

Ceramic 10 pF - 1 µF Variable Variable Average Exact performance of capacitor depends to a

large extent on the ceramic used.

Tantalum0.1 µF - 500 µF

Poor Poor PoorPolarised capacitor - very high capacitance density.

Silver mica1 pF - 3000 pF

Good Good Good

Rather expensive and large - not widely used these days except when small value accurate capacitors are needed.

Polyester (Mylar)

0.001 µF - 50 µF

Good Poor GoodInexpensive, and popular for non-demanding applications.

Polystyrene 10 pF - 1 µF V good Good V goodHigh quality, often used in filters and the like where accuracy is needed.

Polycarbonate100 pF - 20 µF

V good V good Good

Used in many high tolerance and hash environmental conditions. Supply now restricted.

Polypropylene100pF - 50 µF

V good Good V goodHigh performance and low dielectric absorption.

Teflon 100 pF - 1 µF V good V v goodV v good

High performance - lowest dielectric absorption.

Glass10 pF - 1000 pF

Good Good V good

Excellent for very harsh environments while offering good stability. Very expensive.

Porcelain100 pF - 0.1 µF

Good Good Good Good long term stability

Vacuum and air

1 pF - 10 000 pF

Often used as variable capacitors in transmitters as a result of their very high voltage capability.

Summary

There is a huge number of different capacitor types and they are one of the most widely used electronic components. While different capacitors may have the same value, each different type of capacitor has its own properties and this will make this particular electronic capacitor suitable for a particular application. If the wrong type of capacitor is used, then it can make a circuit function incorrectly. As a result, choosing an electronic capacitor for a circuit means making more than the value calculations. Choosing the correct capacitor type is equally important.

Capacitor applications, uses and usage

- notes on capacitor applications, uses and usage, capacitor choice - which type to use in a particular application, circuit or function.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

The choice of capacitor for a particular application or use is of paramount importance. Even if the correct value is chosen for a particular capacitor application or capacitor use, the selection of the correct type is of equal importance.

In some instances one form of capacitor may work very well, but another capacitor type may cause the circuit to not work at all. It is therefore critical that the capacitor use or capacitor application is matched to the type or form of capacitor used.

Table of capacitor uses and applications

The most suitable way to summarise the various types of capacitor and the applications for which these electronic capacitors are suited is in a table.

Application Suitable types with reasons details & comments

Power supply smoothing

Aluminium electrolytic High capacity and high ripple current capability **

Application Suitable types with reasons details & comments

Audio frequency coupling

Aluminium Electrolytic: High capacitance Tantalum: High capacitance and small size Polyester / polycarbonate : Cheap, but values not as high as

those available with electrolytics

RF coupling

Ceramic COG: Small, cheap and low loss Ceramic X7R: Small and cheap but higher loss than COG,

although high capacitance per volume Polystyrene: Very low loss, but larger and more expensive

than ceramic

RF decoupling

Ceramic COG: Small, low loss, but values limited to around 1000 pF max.

Ceramic X7R: Small, low loss, higher values available than for COG types

Tuned circuits

Silver mica: Close tolerance, low loss and stable, but high cost

Ceramic COG: Close tolerance, low loss, although not as good as silver mica

** Care must be taken to ensure that the ripple current rating of the capacitor meets the requirements of the capacitor application.

This table gives the typical capacitor applications or capacitor uses for areas where particular capacitors be used. However it is necessary to look at the exact requirements for any capacitor application in a circuit, and choose the capacitor according to the needs and specifications available.

Summary

The capacitor choice is an integral part of the design of an electronics circuit. Using the correct type for a particular capacitor application is often as important as the choice of value. A variety of considerations for the particular capacitor use of application should be included - stability, value range, series resistance, ripple current and more. Each of these parameters has an impact on the choice of capacitor to be used.

Aluminium Electrolytic capacitors- an overview, information or tutorial about the basics of the aluminium electrolytic capacitor: its construction, properties and the uses of the electrolytic capacitor.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

Today electrolytic capacitors or as they are more correctly termed, aluminium electrolytic capacitors are used in huge quantities. They are very cost effective and able to provide a larger capacitance per volume than other types of capacitor. This gives them very many uses in circuits where high currents or low frequencies are involved. Aluminium electrolytic capacitors are typically used most in applications such as audio amplifiers of all types (hi-fi to mobile phones) and in power supply circuits.

Like any other capacitor, it is necessary to understand the advantages and limitations of these capacitors to enable them to be used most effectively.

Electrolytic capacitor development

The electrolytic capacitor has been in use for many years. Its history can be traced back to the very early days or radio around the time when the first broadcasts of entertainment were being made. At the time, valve wireless sets were very expensive, and they had to run from batteries. However with the development of the indirectly heated valve or vacuum tube it became possible to use AC mains power. While it was fine for the heaters to run from an AC supply, the anode supply needed to be rectified and smoothed to prevent mains hum appearing on the audio. In order to be able to use a capacitor that was not too large Julius Lilienfield who was heavily involved in developing wireless sets for domestic use was able to develop the electrolytic capacitor, allowing a component with sufficiently high capacitance but reasonable size to be used in the wireless sets of the day.

Construction of electrolytic capacitors

The plates of an electrolytic capacitor are constructed from conducting aluminium foil. As a result they can be made very thin and they are also flexible so that they can be packaged easily at the end of the production process. The two plates, or foils are slightly different. One is coated with an insulating oxide layer, and a paper spacer soaked in electrolyte is placed between them. The foil insulated by the oxide layer is the anode while the liquid electrolyte and the second foil act as cathode.

In order to package them the two aluminium foils with the electrolyte soaked paper are rolled together to form a cylinder, and they are placed into an aluminium can. In this

way the electrolytic capacitor is compact while being robust as a result of the protection afforded by the can.

There are two geometries that are used for the connection leads or tags. One is to use axial leads, one coming from each circular face of the cylinder. The other alternative is to use two radial leads or tags, both of which come from the same face of the cylinder.

The lead styles give rise to the descriptions used for the overall capacitors. Descriptions of axial and radial will be seen in the component references.

Electrolytic capacitor properties

There are a number of parameters of importance beyond the basic capacitance and capacitive reactance when using electrolytic capacitors. When designing circuits using electrolytic capacitors it is necessary to take these additional parameters into consideration for some designs, and to be aware of them when using electrolytic capacitors.

1. ESR Equivalent series resistance:   Electrolytic capacitors are often used in circuits where current levels are relatively high. Also under some circumstances and current sourced from them needs to have a low source impedance, for example when the capacitor is being used in a power supply circuit as a reservoir capacitor. Under these conditions it is necessary to consult the manufacturers datasheets to discover whether the electrolytic capacitor chosen will meet the requirements for the circuit. If the ESR is high, then it will not be able to deliver the required amount of current in the circuit, without a voltage drop resulting from the ESR which will be seen as a source resistance.

2. Frequency response:   One of the problems with electrolytic capacitors is that they have a limited frequency response. It is found that their ESR rises with frequency and this generally limits their use to frequencies below about 100 kHz. This is particularly true for large capacitors, and even the smaller electrolytic capacitors should not be relied upon at high frequencies. To gain exact details it is necessary to consult the manufacturers data for a given part.

3. Leakage:   Although electrolytic capacitors have much higher levels of capacitance for a given volume than most other capacitor technologies, they can also have a higher level of leakage. This is not a problem for most applications, such as when they are used in power supplies. However under some circumstances they are not suitable. For example they should not be used around the input circuitry of an operational amplifier. Here even a small amount of leakage can cause problems because of the high input impedance levels of the op-amp. It is also worth noting that the levels of leakage are considerably higher in the reverse direction.

4. Ripple current:   When using electrolytic capacitors in high current applications such as the reservoir capacitor of a power supply, it is necessary to consider the ripple current it is likely to experience. Capacitors have a maximum ripple current they can supply. Above this they can become too hot which will reduce their life. In extreme cases it can cause the capacitor to fail. Accordingly it is necessary to calculate the expected ripple current and check that it is within the manufacturers maximum ratings.

5. Tolerance:   Electrolytic capacitors have a very wide tolerance. Typically this may be -50% + 100%. This is not normally a problem in applications such as decoupling or power supply smoothing, etc. However they should not be used in circuits where the exact value is of importance.

Polarisation

Unlike many other types of capacitor, electrolytic capacitors are polarised and must be connected within a circuit so that they only see a voltage across them in a particular way. The capacitors themselves are marked so that polarity can easily be seen. In addition to this it is common for the can of the capacitor to be connected to the negative terminal.

It is absolutely necessary to ensure that any electrolytic capacitors are connected within a circuit with the correct polarity. A reverse bias voltage will cause the centre oxide layer forming the dielectric to be destroyed as a result of electrochemical reduction. If this occurs a short circuit will appear and excessive current can cause the capacitor to become very hot. If this occurs the component may leak the electrolyte, but under some circumstances they can explode. As this is not uncommon, it is very wise to take precautions and ensure the capacitor is fitted correctly, especially in applications where high current capability exists.

Electrolytic capacitors rating and anticipated life

Great care should be taken not to exceed the rated working voltage of an electrolytic capacitor. Normally they should be operated well below their stated working value. Also in power supply applications significant amounts of current may be drawn from them. Accordingly electrolytic capacitors intended for these applications have a ripple current rating which should also not be exceeded. If it is, then the electronic component may become excessively hot and fail. It is also worth noting that these components have a limited life. It can be as little as 1000 hours at the maximum rating. This may be considerably extended if the component is run well below its maximum rating.

Electrolytic SMD capacitors

Electrolytic capacitors are now being used increasingly in SMD designs. Their very high levels of capacitance combined with their low cost make them particularly useful in many areas. Originally they were not used in particularly high quantities because they were not able to withstand some of the soldering processes. Now improved capacitor design along with the use of reflow techniques instead of wave soldering enables electrolytic capacitors to be used more widely in surface mount format.

Often SMD electrolytic capacitors are marked with the value and working voltage. There are two basic methods used. One is to include their value in microfarads (m F), and another is to use a code. Using the first method a marking of 33 6V would indicate a 33 F capacitor with a working voltage of 6 volts. An alternative code system employs a letter followed by three figures. The letter indicates the working voltage as defined in the table below and the three figures indicate the capacitance on picofarads. As with many other marking systems the first two figures give the significant figures and the third, the multiplier. In this case a marking of G106 would indicate a working voltage of 4 volts and a capacitance of 10 times 10^6 picofarads. This works out to be 10 F

Letter Voltagee 2.5G 4J 6.3A 10C 16D 20E 25V 35H 50

Voltage codes for SMD electrolytic capacitors

Reforming aluminium electrolytic capacitors

It may be necessary to re-form electrolytic capacitors that have not been sued for six months or more. The electrolytic action tends to remove the oxide layer from the anode and this needs to be re-formed. Under these circumstances it is not wise to apply the full voltage as the leakage current will be high and may lead to large amounts of heat being dissipated in the capacitor which can in some instances bring about its destruction.

To reform the capacitor, the normal method is to apply the working voltage for the capacitor through a resistor of around 1.5 k ohms, or possibly less for lower voltage capacitors. (NB ensure that it has sufficient power rating to handle the capacitor in question). This should be applied for an hour or more until the leakage current drops to an acceptable value and the voltage directly on the capacitor reaches the applied value, i.e. virtually no current is flowing through the resistor. This voltage should then be continued to be applied for a further hour. The capacitor can then be slowly discharged through a suitable resistor so that the retained charge does not cause damage.

Electrolytic capacitor overview

Aluminium electrolytic capacitors have many advantages offering a very high capacitance density. Therefore electrolytic capacitors are able to offer high levels of capacitance in very small packages. Now that electrolytic capacitors are available in surface mount packages, their use is assured for many years to come.

Ceramic capacitors- an overview, information or tutorial about the basics of the ceramic capacitor: its construction, technical information, properties and the uses of the ceramic capacitor.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

Ceramic capacitors are one of the most widely used forms of capacitor used in electronics equipment these days. Ceramic capacitors have also been used for many years, being found in valve or tube circuits dating from the 1930s.

Today ceramic capacitors area available in a variety of formats ranging from leaded components to surface mount technology, SMT varieties. As leaded versions disc ceramic capacitors are widely available, and as SMT devices, ceramic capacitors are available in all the common formats. As such these ceramic capacitors are used in virtually every type of electronics equipment.

The actual performance of the ceramic capacitors is highly dependent upon the dielectric used. Using modern dielectrics, very high values are available, but it is also necessary to check parameters such as the temperature coefficient and tolerance. Different levels of performance are often governed by the dielectric used, and therefore it is necessary to choose the type of dielectric in the ceramic capacitor.

Ceramic capacitors range in value from figures as low as a few picofarads to around 0.1 microfarads. In view of the wide range and suitability for RF applications they are used for coupling and decoupling applications in particular. Here they are by far the most commonly used type being cheap and reliable and the loss factor is particularly low although this is dependent on the exact dielectric in use.

Ceramic capacitor basics

Ceramic capacitors are the workhorses of the capacitor world these days. Ceramic capacitors are used in millions as a result of a combination of their cost and performance. There is a wide variety of dielectrics that can be used as described below, but as the name of the ceramic capacitor suggests, they are all ceramic in nature.

In order to ensure that sufficient levels of capacitance can be obtained within a single capacitor package, ceramic capacitors, like types of capacitor have multiple layers. This increases the level of capacitance to enable the required values of capacitance to be achieved.

Ceramic capacitors are available now in three main types although other styles are available:

leaded disc ceramic capacitors for through hole mounting which are resin coated multilayer surface mount chip ceramic capacitors Specialist microwave bare leadless disc ceramic capacitors that are designed to sit in a

slot in the PCB and are soldered in place

Although it is possible to obtain other types of ceramic capacitor, these are the main types that can be found today. Of these the surface mount variety is used in the greatest quantities by far because of the manufacturing methods used these days for electronic equipment.

Ceramic dielectrics

Ceramic capacitors have a variety of different ceramic dielectrics as the basis of the capacitor. Ceramic dielectrics are made from a variety of forms of ceramic dielectric. The exact formulas of the different ceramics used in ceramic capacitors vary from one manufacturer to another but common compounds include titanium dioxide, strontium titanate, and barium titanate.

In view of the wide variation of ceramics used in capacitors the EIA (Electronic Industries Alliance) classifies ceramics into groups. In general the lower the group or class the better the

overall characteristics, but this is usually at the expense of size. Types within each class define the working temperature range, temperature drift, tolerance, etc.

1. Class 1:   Class 1 ceramic capacitors are the most stable forms of ceramic capacitor with respect to temperature. They have an almost linear characteristic and their properties are almost independent of frequency within normal bounds.

The common compounds used as the dielectrics are magnesium titanate for a positive temperature coefficient, or calcium titanate for capacitors with a negative temperature coefficient. Using combinations of these and other compounds it is possible to obtain a dielectric constant of between 5 and 150. Also temperature coefficients of between +40 and -5000 ppm/C may be obtained.

Class 1 capacitors also offer the best performance with respect to dissipation factor. This can be important in many applications. A typical figure may be 0.15%. It is also possible to obtain very high accuracy (~1%) class 1 capacitors rather than the more usual 5% or 10% tolerance versions. The highest accuracy class 1 capacitors are designated C0G or NP0.

2. Class 2:   Class 2 capacitors offer better performance with respect to volumetric efficiency, but this is at the cost of lower accuracy and stability. As a result they are normally used for decoupling, coupling and bypass applications where accuracy is not of prime importance. A typical class 2 capacitor may change capacitance by 15% or so over a -50C to +85C temperature range and it may have a dissipation factor of 2.5%. It will have average to poor accuracy (from 10% down to +20/-80%). Howeer for many applications these figures would not present a problem.

3. Class 3:   Class 3 ceramic capacitors offer a still high volumetric efficiency, but again this is at the expense of poor accuracy and stability and a low dissipation factor. They are also not normally able to withstand high voltages. The dielectric used is often barium titanate that has a dielectric constant of up to about 1250.A typical class 3 capacitor will change its capacitance by -22% to +50% over a temperature range of +10C to +55C. It may also have a dissipation factor of around 3 to 5%. It will have a fairly poor accuracy (commonly, 20%, or -20/+80%). As a result, class 3 ceramic capacitors are typically used as decoupling or in other power supply applications where accuracy is not an issue. However they must not be used in applications where spikes are present as these may damage the capacitor if they exceed the rated voltage.

EIA temperature coefficient codes

In order that the performance of ceramic capacitors can be standardised and easily defined, a set of codes has been defined by the EIA (Electrical Industries Association). These codes

enable ceramic capacitor performance to be defined in an easily managed way. The codes are different, though for class 1 and class 2 ceramic capacitors.

Class 1 capacitor codes:Less common is the EIA code for temperature compensated capacitors. This comprises a three character code:

1. The first character is a letter which gives the significant figure of the change in capacitance over temperature in ppm/C

2. The second character is numeric and gives the multiplier

3. The third character is a letter and gives the maximum error in ppm/C

The table below details what each of the EAI codes means.

First character(letter)

significant figures

Second character(digit)

Multiplier

Third character(letter)

toleranceC 0.0 0 -1 G +/-30B 0.3 1 -10 H +/-60L 0.8 2 -100 J +/-120A 0.9 3 -1000 K +/-250M 1.0 4 +1 L +/-500P 1.5 6 +10 M +/-1000R 2.2 7 +100 N +/-2500S 3.3 8 +1000T 4.7V 5.6U 7.5

As an example, one common type of class 1 capacitor is a C0G and this will have 0 drift, with an error of �30PPM/C.

Class 2 capacitor codesIn order to define the class of temperature coefficient of a particular capacitor, a three letter code designated by the EIA is used. For non-temperature-compensating capacitors this EIA code comprises of three characters:

1. The first character is a letter. This gives the low-end operating temperature.

2. The second is numeric and this provides the high-end operating temperature.

3. The third character is a letter which gives capacitance change over that temperature range.

The table below details what each of the EAI codes means.

First character(letter)

low temperature

Second character(digit)

high temperature

Third character(letter)change

X -55C (-67F) 2 +45C (+113F) D +/-3.3%Y -30C (-22F) 4 +65 (+149F) E +/-4.7%Z +10C (+50F) 5 +85 (+185F) F +/-7.5%

6 +105 (+221F) P +/-10%7 +125 (+257F) R +/-15%

S +/-22%T +22% / -33%U +22% / -56%V +22% / -82%

Two very common examples of class 2 ceramic capacitors are the X7R capacitor which will operate from -55�C to +125�C with a capacitance change of up to �15%, and the Z5U capacitor which will operate from +10�C to +85�C with a capacitance change of up to +22% to -56%.

SMD / SMT ceramic capacitors

The vast majority of ceramic capacitors that are used today are in the form of surface mount technology devices. Millions of these ceramic capacitors are used every day in every form of mass produced electronics equipment.

SMD / SMT ceramic capacitors are shaped in the form of a rectangular block or cuboid. The capacitor itself consists of the ceramic dielectric in which a number of interleaved precious metal electrodes are contained. This structure gives rise to a high capacitance per unit volume. The inner electrodes are connected to the two terminations, either by silver palladium (AgPd) alloy in the ratio 65 : 35, or silver dipped with a barrier layer of plated nickel and finally covered with a layer of plated tin (NiSn).

Care must be taken when soldering these capacitors. If heat is applied for too long, then the terminations can be damaged. Fortunately modern versions are far more robust than much older capacitors which used to suffer from metalisation if heat was applied for too long. Despite this care should be taken, especially if these components are being soldered manually. Normally production methods using infra-red reflow with carefully controlled heat profiles is to be recommended.

SMT / SMC ceramic capacitors are normally contained within standard package sizes. These have various designations as described in the table below:

Package designationSize

(mm)Size

(inches)1812 4.6 � 3.0 0.18 � 0.121206 3.0 � 1.5 0.12 � 0.060805 2.0 � 1.3 0.08 � 0.05)0603 1.5 � 0.8 0.06 � 0.030402 1.0 � 0.5 0.04 � 0.020201 0.6 � 0.3 0.02 � 0.01

Capacitor package designations

It can be noted that the package designation is derived from the package size in 0.01 inch increments.

Wired ceramic capacitors

While the majority of ceramic capacitors that are used are in the form of SMT or SMD components, large quantities of wired components are still used. A large proportion of the wired ceramic capacitors are in the form of disc ceramic capacitors. As the name suggests these electronic components are shaped in the form of a disc.

Ceramic capacitor summary

Ceramic capacitors are one of the most convenient and cost effective forms of capacitor to use. They are cheap, reliable and offer very high levels of performance. In terms of their use in surface mount technology, ceramic capacitors are able to provide the small sizes require, while retaining sufficient levels of capacitance. To enable all these requirements to be fulfilled significant levels of development have been required, and despite the fact that they are produced in billions, ceramic capacitor technology is highly advanced and new developments are being made all the time.

Tantalum capacitors- an overview, information or tutorial about the basics of the tantalum capacitor: its construction, properties and the uses of tantalum capacitors.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

Tantalum capacitors are widely used in electronics design these days. Tantalum capacitors offer a form of capacitor that provides a very high capacity density. As a result this form of capacitor has found widespread use in many areas of electronics. In view of its size and the attainable levels of capacitance, these capacitors are widely used in many mass produced items of electronics equipment.

The tantalum capacitor is similar to the electrolytic capacitor, but using tantalum within the construction of the capacitor it is able to offer extremely high levels of capacitance for any given volume. As such tantalum capacitors are widely used in electronics equipment where there is a need for small size and a high level of capacitance. In view of its advantages, the tantalum capacitor is used in large volumes within the electronics manufacturing industry.

Types of tantalum capacitor

While tantalum capacitors are widely used, it is not so well known that there are three types of tantalum capacitor that are available:

Tantalum foil electrolytic capacitor:   The tantalum foil capacitor was introduced around 1950. It was developed to provide a more reliable form of electrolytic capacitor without the shelf life limitations of the aluminium electrolytic capacitor. It was able to be developed as a result of the availability of high purity tantalum foils and wires. Initially plain foil variants were introduced, but this was quickly followed by etched variants.

The purity of the materials used plays a major part in determining the leakage current of this type of tantalum capacitor.

These tantalum capacitors have a higher capacitance density than their aluminium electrolytic counterparts. They can often operate at temperatures up to about 120C and therefore they are often used in equipment used in extreme conditions.

Tantalum capacitors with porous anode and liquid electrolyte:   This form of tantalum capacitor is also known as the wet tantalum capacitor and it was the first form to be introduced. It still offers the best space factor.

A variety of electrolytes can be used within this form of tantalum capacitor. Those using sulphuric acid as the electrolyte have excellent electrical characteristics and the maximum working voltages that are manufactured tend to be a maximum of about 70 volts.

Basically this type of capacitor consists of a sintered porous anode of tantalum power. This is housed in a silver or silver plated container. The porous anode is made by pressing high purity tantalum power into a cylindrical body and then sintering in a vacuum at about 2000C.

These wet tantalum capacitors are very much more expensive than their newer brothers and as a result they are not as widely used.

Tantalum capacitors with porous anode and solid electrolyte:   This variant of the tantalum capacitor family is also known as the solid tantalum, and it is the variety that is most commonly used. Many millions of them are sued each day, and they can be found in many items of consumer and commercial electronic equipment.

The capacitor was developed by the Bell Telephone Laboratories by using a porous anode and then replacing the liquid electrolyte with a solid semiconductor. This overcome the problem od requiring a vent that is common to all other forms of electrolytic capacitor.

These capacitors are superior to electrolytic capacitors in many ways exhibiting excellent temperature and frequency characteristics. They are also smaller than their aluminium electrolytic counterparts. However they are not able to handle high levels of current or voltage spikes. They are also damaged almost instantaneously by reverse polarity - usually exploding quite nicely.

Leaded tantalum capacitors

The most common form of leaded tantalum capacitors in use today are the "solid" tantalum capacitors. They offer particularly small package sizes and as a result they have been widely used in many areas of electronics.

Leaded tantalum capacitors (solid tantalum variety) are generally small and encapsulated in epoxy to prevent damage. The capacitor marking may be written directly onto the encapsulation as figures, although many used a colour coding system.

Warning: - In view of the nature of these capacitors, great care should be taken not to stress these capacitors. The polarity should not be reversed, nor should they be exposed to over-voltage conditions - even spikes. If they are exposed to these conditions then they may fail,

sometimes exploding.

Tantalum SMD capacitors

Tantalum SMD capacitors are widely used to provide levels of capacitance that are higher than those that can be achieved when using ceramic capacitors. The capacitor technology that is used within SMD tantalum capacitors is based on the solid tantalum capacitor technology. This is robust and enables very small capacitors to be made.

For many years tantalum capacitors were used in SMD applications because electrolytic capacitors were not able to survive the high temperatures of the soldering process. Now that electrolytic capacitor technology has been developed to withstand the soldering process, these capacitors are now also widely used. Despite this, the other advantages of tantalum capacitors are employed in many circuits, and they are still used in vast quantities.

As a result of the different construction and requirements for tantalum SMT capacitors, there are some different packages that are used for them. These conform to EIA specifications.

Package designationSize

(mm)EIA designation

Size A 3.2 x 1.6 x 1.6 EIA 3216-18Size B 3.5 x 2.8 x 1.9 EIA 3528-21Size C 6.0 x 3.2 x 2.2 EIA 6032-28Size D 7.3 x 4.3 x 2.4 EIA 7343-31Size D 7.3 x 4.3 x 4.1 EIA 7343-43

Tantalum capacitor advantages and disadvantages

tantalum capacitors offer many advantages over other types of capacitor. This has meant that their use has risen considerably over the years, and now they are widely used in all forms of electronics equipment. The advantages of tantalum capacitors can be summarised:

Volumetric efficiency:   Tantalum capacitors offer a very high level of volumetric efficiency - much greater than many other types. In particular they are better than electrolytic capacitors which are their main rival.

Good frequency characteristics:   The frequency response of tantalum capacitors is superior to that of electrolytic capacitors. This means that they are more suitable for use in a number of applications where electrolytics could not be used.

High reliability:   Tantalum capacitors are more reliable than many other forms of capacitor. Provided they are operated within their ratings they are able to provide an almost unlimited life. Their use is not time limited as in the case of electrolytic capacitors.

Wide operating temperature range:   Tantalum capacitors are able to operate over a very wide temperature range. They are often specified for operating over the range -55C to +125C. This makes them an ideal choice for use in equipment for use in harsh environmental conditions.

Compatibility with modern production methods:   Modern production techniques often expose components to high temperatures during soldering as the whole assembly is heated by infra-red heat. Using conventional leaded components only the board surface was heated and the amount of heat conducted by the leads was usually insufficient to damage the components. Tantalum capacitors are able to withstand the temperatures of SMT production and are there fore ideal for use in many new electronics designs.

Tantalum capacitors have a number of disadvantages, and these need to be considered when using them in new designs.

Low ripple current ratings:   It is hardly surprising in view of their size, that tantalum capacitors do not have a high ripple current rating. They should not normally be used in areas that require any levels of current to be passed.

Not tolerant to reverse or excess voltage:   Tantalum capacitors do not like reverse or excess voltage. Even spikes can destroy them. If they are exposed to excess or reverse voltages then they can explode.

More expensive than other types:   Tantalum capacitors are more expensive than many other forms of capacitor. As a result their cost should be considered during the design phase as the other benefits may outweigh any increased costs.

Tantalum capacitor summary

Tantalum capacitors are a particularly useful form of capacitor. They offer a high capacity density, and provided they are operated within their ratings, they offer a high degree of reliability. Also they lend themselves to surface mount technology and in this guise tantalum capacitors are used in vast quantities each day.

Polycarbonate capacitors- an overview, tutorial about the basics of the polycarbonate capacitor or polycarbonate film capacitor: its construction, properties and general data and information.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

The polycarbonate capacitor has been available for many years. The polycarbonate dielectric material is very stable having a high tolerance and can operate over a temperature of range of typically -55�C to +125�C without de-rating. Additionally the insulation resistance and dissipation factor are good and the dielectric constant means that polycarbonate capacitors are a reasonable size for their capacitance.

While polycarbonate capacitors have been widely used within many electronics circuits and found favour with many electronics design centres, they are not as widely used these days. The Bayer Corporation which manufactures the majority of polycarbonate announced in 2000 that it was to discontinue production of the dielectric film used in these capacitors. Although many saw this as the end of polycarbonate capacitors, there are still some smaller sources of the dielectric material and some capacitors are still made. However many are cautious about using polycarbonate capacitors in new electronics designs as there are fewer suppliers, and relying on a single source for the long term supply of an electronics component is not wise.

Polycarbonate dielectric

Polycarbonates are a group of thermoplastic polymers which find uses in many areas of industry as they are easily moulded and thermoformed. They also posses a number of useful features in that they are temperature resistant impact resistant (virtually bullet-roof). They can also be used for vandal-proof glazing.

Polycarbonate is also used in capacitors as a dielectric. Polycarbonate is very stable, offering the possibility of high tolerance capacitors that can be used over a wide temperature range, and shows little sign of ageing.

The basic electrical properties of polycarbonate are summarised below:

Parameter ValueDielectric constant 3.2

Dissipative factor0.0007 @ 50Hz0.001 at 1MHz

Volume resistivity 10-17 ohm cmDielectric strength 38 kV / mmWater absorption 0.16%

Polycarbonate capacitor construction

Polycarbonate dielectric capacitors are typically manufactured in an extended foil format. Metallized electrodes are then used to make the connections. This dielectric is made from a solvent casting process and performs best as a metallized construction. Metallized types feature vapour deposited metal electrodes and give significant size savings, a definite plus in precision applications. In addition, they feature self-healing. Self-healing removes a fault or short circuit by vaporizing the electrode in the region of the short and restores the capacitor to useful life, thereby greatly extending the lifetime of the capacitor.

Polycarbonate capacitor encapsulation

The encapsulation of the polycarbonate capacitor is important, and a variety of different types can be used. Typically the capacitor may be contained within an epoxy moulded encapsulation, but other popular alternatives include a metal enclosure or preformed box assembly.

It is important to choose the encapsulation required for the particular environment in which the capacitor will be used because the polycarbonate dielectric is sensitive to moisture which can be absorbed as seen by the figures given in the electrical properties section. This water absorption in the polycarbonate dielectric will naturally change some of the electrical properties.

Polycarbonate capacitor applications and use

Polycarbonate capacitors have been used in a wide variety of applications because of the superior performance offered. Typically they are used in applications where precision capacitors are needed (less than �5%). They are generally used in electronics circuits such as filters, as well as for timing and precision coupling applications.

Polycarbonate capacitors can also be used for AC applications. They are sometimes found in switching power supplies. Care must be taken when using them in these applications. Although the dissipation factor is low, the current must be restricted to prevent them from overheating, although they can tolerate temperature better than many other types of capacitor.

Polycarbonate capacitor replacements

With polycarbonate capacitors being less widely available these days since the Bayer Corporation ceased production of polycarbonate in a form suitable for use as a dielectric, a number of alternative types of capacitor have been sought, especially for use in some military applications where capacitors to a given standard need to be used. A variety of types can be used as almost direct replacements:

Polyethylene napthalate (PEN)

Polyphenylene sulphide (PPS) Polyimide (PI) Polytetrafluoroethylene (PTFE

Of these polyphenylene sulphide, PPS is being widely used in many areas as an almost direct replacement.

Polyphenylene sulphide, PPS has many of the same characteristics of polycarbonate and can be often be used as a direct replacement. It has gaining a variety of MIL standards and as such it is being used in many high specification applications. PPS has been found to have a superior temperature performance both in terms of the temperature range applicable and the temperature coefficient.

It is found that polyphenylene sulphide, PPS and polycarbonate have the almost the same dielectric constant. This means that the size of equivalent capacitors will be virtually the same, making replacement in existing designs much easier. Unfortunately not all capacitors will be able to be made exactly the same size because PPS and polycarbonate are not available in the same thicknesses.

Polycarbonate capacitor summary

Polycarbonate capacitors have been in use for many years. Since the introduction of polycarbonate as a dielectric in 1958, they have been used as a precision capacitor in many forms of electronics circuit. Although the Bayer Corporation as the main supplier of polycarbonate has ceased its production for use as a dielectric in capacitors, some are still available as a few companies are still able to produce these capacitors. However it would be anticipated that other forms of capacitor would now be used as alternatives in new designs.

Silver Mica Capacitor- an overview or tutorial about the basics of the silver mica capacitor, its construction, properties and the uses of silver mica capacitors particularly in RF circuits.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

Silver mica capacitors have been widely used as high performance capacitors over the years. Although silver mica capacitors are not as widely used, these days, nevertheless they are still available and used in a variety of applications where their particular properties are needed.

Silver mica capacitors are able to provide very high levels of accuracy, stability and low loss. As a result silver mica capacitors found many uses in radio frequency applications, particular for oscillator and filter circuits where their stability, accuracy and low loss (leading to high Q) were needed. Although not as widely used these days, they can still be obtained and are used where stability of value is of the utmost importance and where low loss is required.

Two main reason for the decline in the use of silver mica capacitors is their size, resulting from the materials used and their construction. The cost of silver mica capacitors is higher than many other types that can often be used these days.

Silver mica capacitor properties

The reason for the continued use of silver mica capacitors is the fact that they can offer very high levels of performance, better in many areas than any other type of capacitor. However in many applications, other more modern technologies provide levels of performance that meets the needs for that particular requirement.

The particular properties of the silver mica capacitor are summarised below:

High accuracy:   Silver mica capacitors can be obtained with tolerance figures of +/- 1%. This is much better than virtually every other form of capacitor available today.

Temperature co-efficient:   The temperature co-efficient of silver mica capacitors is much better than most other types of capacitor. The temperature coefficient is positive and is normally in the region 35 to 75 ppm / C, with +50 ppm / C being an average value

Value range:   Values for silver mica capacitors are normally in the range between a few picofarads up to two or possibly three thousand picofarads.

Low capacitance variation with voltage :   Silver mica capacitors exhibit very little voltage dependence.

High Q :   Silver mica capacitors have very high levels of Q and conversely small power factors. These are both almost independent of frequency.

Although silver mica capacitors have a high tolerance and low temperature co-efficient they are known to jump in value on occasions.

Mica dielectric

The mica dielectric obviously forms the basis for silver mica capacitors. Its properties govern the performance of the silver mica capacitor. It was also one of the first dielectric materials to be used for capacitors in the early days or wireless because of its combination of stability and general physical and mechanical attributes.

Although there are several different forms of mica, they all have very similar properties. They are fundamentally very stable both mechanically and chemically, enabling the capacitors manufactured with mica to exhibit similar properties. The material has a dielectric constant ranging from around 5 to 7.

It is also found that the crystalline structure of mica has binding forces that are different in different planes. In one plane they are strong, but weak in the perpendicular plane. This gives it a layered structure and enables it to be spilt along the lines of the weak bond into very thin flat sheets. The sheets used in capacitor manufacture are from less than about 0.025 to 0.1 mm.

Natural mica has to be carefully selected because some samples do contain impurities including, iron, sodium, ferric oxide, and lithium. This introduces some variability into any mica that might be used for capacitor manufacture and therefore it must be carefully inspected and classified. This is one of the reasons why silver mica capacitors are more expensive than other types which have less manual intervention.

Mica is chemically very stable and chemically inert. Mica does not react with oil, water, many acids alkalis, and solvents. As a result of this, ageing does not occur to any major degree, and the variations of water vapour in the atmosphere do not cause undue variations in the overall capacitor performance.

Although more costly than other dielectrics, mica is an ideal form of dielectric for very high performance capacitors such as silver mica capacitors. A summary of the properties of mica are given below:

Parameter ValueDielectric constant 6Dielectric strength 10 000 volts per mil

Construction

For silver mica capacitors the silver electrodes are now plated directly on to the mica dielectric, although originally thin sheets of silver foil were placed between the mica dielectric. Again several layers are used to achieve the required capacitance. Wires for the connections are added and then the whole silver mica capacitor assembly is encapsulated to provide protection.

Today a ceramic encapsulation is used, although early versions, used in some valve or vacuum tube radios can be seen to have a form of wax encapsulation. This was effective for the day in protecting the capacitor from moisture, but when warmed, the wax melted, and often these capacitors had little wax on them from the warm environment of a vacuum tube or valve radio.

Silver mica capacitor summary

Silver mica capacitors are not widely used these days, although they can be seen in some specialist applications. Silver mica capacitors still offer levels of performance that cannot be equally by most other forms of capacitor. As such they are still available and used in a variety of applications where particularly high levels of performance are needed.

Glass capacitors- an overview or tutorial about the basics of the glass capacitor, its construction, properties and the uses of glass dielectric capacitors particularly in RF circuits.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

Glass capacitors are used where the ultimate performance is required for RF circuits. Glass dielectric capacitors offer very high levels of performance, although their cost is high when compared to many other forms of capacitor. Typically a glass capacitor will have a relatively low capacitance value. The values of glass capacitors may range between a fraction of a picofarad up to two to here thousand picofarads. As such these capacitors are used mainly in radio frequency circuit design.

While the performance of glass capacitors is exceedingly high, this is also usually reflected in the cost - it can run into many pounds or dollars for each component. As such glass dielectric capacitors are reserved only for the most exacting RF requirements, often on low volume products where cost is not such an issues as it is in high volume products. The supply of glass capacitors is also limited to a small number of manufacturers and suppliers, and the capacitors may not be available ex-stock.

Glass capacitor advantages and characteristics

Glass capacitors offer several advantages over types of capacitor. In particular glass capacitors are applicable for very high performance RF applications:

Low temperature coefficient:   Glass capacitors have a low temperature coefficient. Figures of just over 100 ppm / C are often obtained for these capacitors.

No hysteresis:   Some forms of capacitor exhibit hysteresis in their temperature characteristic. This is not the case for glass capacitors which follow the same temperature / capacitance when the temperature is rising and falling.

Zero ageing rate:   Many electronics components change their value with age as chemical reactions take place within the component. Glass capacitors do not exhibit this effect and retain their original value over long periods of time.

No piezo-electric noise :   Some capacitors exhibit the piezo-electric effect to a small degree. This can result in effects such as microphony on oscillators. Where this could be a problem, the use of glass capacitors could help solve the problem.

Extremely low loss / High Q:   Glass capacitors are very low loss as there is virtually no dielectric loss. This enables very high Q circuits to be built using them. provided the other components (e.g. inductors) are not lossy.

Large RF current capability:   Some capacitors are not able to withstand large values of current. This is not the case for glass capacitors which are suitable for use in RF high power amplifiers, etc.

High operating temperature capability :   Glass dielectric capacitors are able to operate at very high temperatures. Many are able to operate at temperatures up to about 200C without fear of damage or performance shortfall.

Glass capacitor construction

The construction of glass dielectric capacitors is relatively straightforward to understand. The capacitor consists of three basic elements: the glass dielectric, aluminium electrodes and the encapsulation. However the assembly of the glass capacitors is undertaken in a manner that ensures the required performance is obtained.

As the capacitance between two plates is not always sufficient to provide the required level of performance, the majority of capacitors use a multiplayer construction to provide several layers of plates with interspersed dielectric to give the required capacitance.

Although the glass plates are always flat, and tubular forms of construction are not applicable, the glass capacitors are usually available with leads emanating in either a radial or axial form. Essentially the leads either exit the encapsulation at the side or the end.

Glass capacitor applications

Glass capacitors can find applications in many areas as a result of their performance characteristics. They do tend to be specialist components and are normally fairly costly.

Circuits exposed to temperature extremes:   With the tolerance to a wide range of temperatures, both high and low, some circuits that may be exposed to very harsh environmental conditions may choose to use glass capacitors. Not only can they withstand high and low temperatures, but they do not change value at these extremes by a great amount. Accordingly remote sensors may choose to use glass capacitors.

Applications requiring a high Q circuit:   Many circuits including oscillators and filters may require high Q components to give the required performance. Filters will be able to attain their required bandwidth, and for oscillators there are a number advantages including improvement of phase noise performance, reduction in drift and reduction of spurious oscillations.

Low microphony requirements:   It may be expedient to use glass capacitors in circuits where microphony may be a problem. RF oscillators including those found in phase locked loops and PLL synthesizers may benefit from their use.

High power amplifiers:   The high current capability of glass capacitors may enable their use in RF power amplifiers where other forms of capacitor would not be suitable.

High tolerance areas:   In many areas such as filters or free running oscillators the high tolerance and precision accompanied by the low temperature coefficient may be required to maintain the tolerances within a precision circuit.

Glass capacitor summary

Glass dielectric capacitors are viewed as specialist capacitors, but in view of their properties, they offer real advantages in many applications over all other forms of capacitor. Their combination of robustness and high tolerance is a rare combination that sets them above all other forms of component. It is only their size and cost that limits their use. However where these two issues are not critical, then glass a glass capacitor may solve a problem in a circuit that may otherwise not work properly in the particular environment in which it may need to operate.

Polystyrene capacitor

- summary and notes on the polystyrene capacitor or polystyrene capacitor detailing its properties, advantages and disadvantages.

This overview of the different types of capacitor is split into several pages:

[1] Capacitor types [2] Capacitor uses and applications [3] Electrolytic capacitor overview [4] Ceramic capacitor [5] Tantalum capacitor [6] Polycarbonate capacitor [7] Silver mica capacitor [8] Glass dielectric capacitor [9] Polystyrene capacitor

Polystyrene capacitors are used within a limited number of applications. Polystyrene capacitor construction does not lend itself to surface mount technology and accordingly polystyrene capacitors tend to be used for leaded applications.

As a result of their construction and limited use, polystyrene capacitors are not widely sued these days and can be difficult to source.

Polystyrene capacitor properties

Polystyrene capacitors are not widely available these days, however they still find applications within audio circles. This is as a result of their electrical characteristics which lend them to these applications.

The polystyrene capacitors provide a number of electrical characteristics which make them suitable for a number of applications. These capacitors provide high insulation, low leakage, low dielectric absorption, low distortion and excellent temperature stability.

In view of their properties, polystyrene capacitors can often be used in place of silver mica or ceramic disc capacitors.

Polystyrene capacitor advantages and disadvantages

While the polystyrene capacitor has many advantages it also has a number of disadvantages as well.

Polystyrene capacitor advantagesPolystyrene capacitor

disadvantages High insulation Low leakage Low dielectric absorption Low distortion (audio enthusiasts

like them because of this) Good temperature stability

Technology does not lend itself to SMT

Not heat resistance - polystyrene melts

Very limited availability

Polystyrene dielectric properties

The dielectric used within polystyrene capacitors has a number of properties which enable them to have excellent properties for many applications.

Property DetailsDielectric constant 2.5 - 2.6Dielectric strength 19.7 MV/m

Loss tangent0.0001 @ 100 MHz0.00033 @ 3 GHz

Polystyrene capacitor summary

While polystyrene capacitors may offer excellent performance, they should not be considered for new designs. Polystyrene capacitors are relatively large for the capacitance they offer and in addition to this polystyrene capacitors are not available in surface mount technology. This means that their future use will be very limited and suppliers and manufacturers will become less.