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Capacitor uses - essential tips about where to use the different types of capacitor

Capacitor types - information about the different types of capacitor

Capacitor types

- a tutorial, overview or summary of the different types of capacitor that are available.

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 has its own advantages and disadvantages can be used in different applications, and 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.

Capacitor attributes
Capacitors can be used in a variety of different ways in electronics circuits. Although their mode of operation remains exactly the same, they can be used to provide a variety of different circuit functions:

• Coupling capacitor   to allow AC signals to pass from one section of a circuit to another while blocking any DC components.



• Decoupling capacitor   to remove any AC signals that may be on a DC bias point or power rail.



• Smoothing capacitor   This is effectively the same as a decoupling capacitor, but the term is normally used in conjunction with a power supply.



• Timing element &nbps; In this application a capacitor can be used with a resistor or inductor in a resonant or time dependent circuit. In this function the capacitor may appear in a filter, oscillator tuned circuit, or in a timing element for a circuit such as an astable, the time it takes to charge and discharge determining the operation of the circuit



• Etc.   there are many other ways in which capacitors can be used.

In addition to the function within a circuit, there is also the frequency of operation that is of importance. Some capacitors operate better at low frequencies, whereas others are better at high or radio frequencies.

Capacitor types
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, noot 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.

1. Ceramic
   As the name indicates, ceramic capacitors gains their name from the fact that they use 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 and as a result ceramic capacitors typically range in value from a few picofarads up to values around 0.1 uF.
   
   There is a variety of types of dielectrics, the more common forms are:
   
   
   • 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 elvels 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.
   
   
   
2. Electrolytic
   The electrolytic capacitor is the most popular type for values greater than about 1 microfarad, having the one of the highest levels of capacitance for a given volume. It 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.
   
   These 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.
   
   These 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. They do not operate well at high frequencies and are typically not used for frequencies above 50 - 100 kHz.



3. Plastic film capacitors
   There is a number of different types of plastic film capacitors. Polycarbonate, polyester and polystyrene are some of the most common. Each has its own properties, allowing them to be used in specific applications. Their values may range anywhere from several picofarads to a few microfarads dependent upon the actual type. 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
   
   
   
4. 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.
   
   Silver mica capacitors are not as widely used these days as they used to be. 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.



5. 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.

Summary
It can be seen from even the selection of the most commonly used capacitors, that many types 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. If the wrong sort is used, then its performance many not be to the standard needed for the circuit.