Capacitor Applications, Uses & Usage

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

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.

A wide variety of different capacitors is available to meet a variety of capacitor applications and capacitor uses. Choosing the right one is key to the performance of the circuit..

Factors associated with capacitor choice

When choosing a particular type of capacitor, there are many factors that determine the best choice. Some of the major capacitor parameters are detailed below:

  • Value range available:   Certain capacitors are available in certain ranges and this often limits the capacitor choice. Determining the ranges available may guide some initial decisions on the choice for a given capacitor application.
  • Working voltage:   Another major factor determining the capacitor choice and application is the working voltage. Some capacitors, such as tantalum ones, tend to be available in lower voltages, whereas others like ceramic capacitors have a much wide operating range. Looking at the working voltage needed may have an impact on the capacitor usage and choice.
  • Polarisation:   capacitors like electrolytic and tantalum capacitors are polarised and can only operate with a voltage in one direction across them. This may impact the choice of capacitor is voltages in either direction are needed for the particular use in mind.
  • Tolerance:   For some coupling and decoupling applications the exact value of the capacitor is not critical. However in some circuits and applications such as filters and oscillators the value of the capacitor may be critical. For these applications close tolerance capacitors may need to be chosen.
  • Temperature coefficient:   Some capacitors vary considerably with temperature. Some, like silver mica or some forms of ceramic are vary little with temperature and are therefore suitable for applications in oscillators and filters.
  • Leakage current:   In some applications, there is a need to a high level of insulation cross the capacitor. For other applications this may not be so important. Electrolytic capacitors have poor leakage performance levels and this should be included in any decisions made.
  • Cost:   In many capacitor applications cost can be a driving issue. Today, even many high performance capacitors can be obtained for relatively low cost in surface mount packages. Silver mica, glass and other specialised types with exceedingly high levels of performance can be very costly, but these are not normally required for most applications.

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. This incorporates many of the different capacitor parameters from available ranges to performance, tolerance, etc. However when making a choice of capacitor for a particular use, then its performance should be investigated for the given application.

Table of capacitor uses and applications
Capacitor Application Suitable types with reasons details & comments

Power supply smoothing applications
  • Aluminium electrolytic   High capacity and high ripple current capability **

Audio frequency coupling uses
  • 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 capacitor applications
  • 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 applications
  • 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 circuit uses
  • 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.

By Ian Poole

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