Capacitor Tutorial Includes:
Capacitor uses Capacitor types Electrolytic capacitor Ceramic capacitor Tantalum capacitor Film capacitors Silver mica capacitor Super capacitor SMD capacitor Specifications & parameters How to buy capacitors - hints & tips Capacitor codes & markings Conversion table
Capacitors are used in virtually every electronics circuit that is built today. Capacitors are manufactured in their millions each day, but there are several different capacitor types that are available.
Each type of capacitor has its own advantages and disadvantages can be used in different applications.
Accordingly it is necessary to know a little about each capacitor type so that the correct one can be chosen for any given use or application.
There are very many different capacitor types that can be bought and used in electronics circuits.
While the list below gives some of the major capacitor types, not all can be listed and described and there are some less well used or less common types that can be seen. However it does include most of the major capacitor types.
- Ceramic capacitor: As the name indicates, this type of capacitor gains its name from the fact that it uses a ceramic dielectric. This gives the many properties including a low loss factor, and a reasonable level of stability, but this depends upon the exact type of ceramic used. Ceramic dielectrics do not give as high a level of capacitance per unit volume as some types of capacitor and as a result ceramic capacitors typically range in value from a few picofarads up to values around 0.1 µF.
For leaded components, disc ceramic capacitors are widely used. This type of ceramic capacitor is extensively for applications like decoupling and coupling applications. More highly specified capacitors, especially used in surface mount types of capacitor often have specific types of ceramic dielectric specified. The more commonly seen types include:
- COG: Normally used for low values of capacitance. It has a low dielectric constant, but gives a high level of stability.
- X7R: Used for higher capacitance levels as it has a much higher dielectric constant than COG, but a lower stability.
- Z5U: Used for even higher values of capacitance, but has a lower stability than either COG or X7R.
- Electrolytic capacitor: This type of capacitor is the most popular leaded type for values greater than about 1 microfarad, having the one of the highest levels of capacitance for a given volume. This type of capacitor is constructed using two thin films of aluminium foil, one layer being covered with an oxide layer as an insulator. An electrolyte-soaked paper sheet is placed between them and then the two plates are wound around on one another and then placed into a can.
Electrolytic capacitors are polarised, i.e. they can only be placed one way round in the circuit. If they are connected incorrectly they can be damaged, and in some extreme instances they can explode. Care should also be taken not to exceed the rated working voltage. Normally they should be operated well below this value.
This capacitor type has 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. They do not operate well at high frequencies and are typically not used for frequencies above 50 - 100 kHz. . . . . Read more about electrolytic capacitors.
- Plastic film capacitors: There are two main formats for the construction of plastic film capacitors:
- Metallised film: In this type of film capacitor the plastic film has a very thin layer of metallisation deposited into the film. This metallisation is connected to the relevant connection on one side of the capacitor or the other.
- Film foil: This form of film capacitor has two metal foil electrodes that are separated by the plastic film. The terminals are connected to the end-faces of the electrodes by means of welding or soldering.
Normally they are non-polar. In general they are good general-purpose capacitors that may be used for a variety of purposes, although their high frequency performance is not usually as good as that of the ceramic types. Some of the more common types include:
- Mylar - Can introduce noise when used in applications where there is vibration.
- Polycarbonate - Moderate level of loss which can increase with frequency. Very high insulation resistance.
- Polyester - Moderate level of loss which can increase with frequency. Very high insulation resistance.
- Polystyrene - tend to be very low loss but bulky. Have a temperature coefficient of around -150 ppm / C
- Tantalum: 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 electrolytics and instead of using a film of oxide on aluminium they us a film of oxide on tantalum. They 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, tantalums 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. . . . . Read more about tantalum capacitors.
- Silver Mica: Silver mica capacitors are manufactured by plating silver electrodes directly on to the mica film dielectric. To achieve the required capacitance, several layers are used. Wires for the connections are added and then the whole assembly is encapsulated. The values of silver mica capacitors range in value from a few picofarads up to two or three thousand picofarads.
This type of capacitor is not as widely used these days. However they 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. . . . . Read more about silver mica capacitors.
- Supercap Super capacitors with capacitance levels of a Farad or more are now becoming more commonplace. These super capacitors are generally used for applications like memory hold up and the like.
They are too large for use in most circuits and their frequency response is limited, but they make ideal hold up capacitors, being able to provide residual current and voltage to retain memory for periods when power may be removed. . . . . Read more about super capacitors.
Capacitor types overview
It can be seen from even the selection of the most commonly used types of capacitor, that many forms are available. Each has its own advantages and disadvantages, and if the right one is chosen for each job, then it can perform very well in a circuit. It is for this reason when building circuits that it is important to use the right type of capacitor. If the wrong sort is used, then its performance many not be to the standard needed for the circuit.
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