composants:capacitors [mh8 Wiki]

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====== Capacitors ======

Used to store electrical charge. It is composed of two sheets of metals separated by a dielectric medium.

Capacitance is measured in Farad (F) but it is a large unit. Mostly used is pF, nF, µF or mF.

===== Types of capacitors =====

Class I capacitors have better accuracy and low volumetric efficiency whereas class III capacitors have low accuracy and high volumetric efficiency.

==== Ceramic capacitors ====

{{composants:ceramic_capacitor.jpg?300}}

Ceramic capacitors do not have any polarity. The dielectric medium is composed of a thin ceramic layer.

Ceramic capacitors don't always have their capacitance indicated. Sometimes it's just a number. You can use a chart like [[http://www.electronicsteacher.com/capacitor-chart.php|this one]] to get the capacitor value

==== Electrolytic capacitors ====

{{composants:electrolytic_capacitor.jpg?300}}

Most of the electrolyte capacitors are polarized. Electrolytic capacitors are known to have a higher volumetric efficiency. This means a small capacitor is able to hold larger amount of charges than a ceramic capacitor of the same size.

If they are connected with the wrong polarity, they may become very hot and may even explode. 

=== ESR ===

For electrolytic capacitors, the **Equivalent Series Resistance (ESR)** is an important concept. If the ESR is too high, then the current flow through the circuit would be too small. The figure below shows how the ESR (impedance) of a capacitor changes with resistance. Each curve shows different capacitance values:

{{composants:capacitor_esr.jpg?500}}

Note that for each type of capacitor, there is a frequency at which the impedance is at a minimum. This frequency is the **resonant frequency** of the capacitor. Note that as the capacitance becomes larger, the resonant frequency becomes smaller.

==== Comparison ====

  *Ceramic capacitor has two metal sheets at the terminals to store charges. The electrolytic capacitor has one metal sheet and an ionic liquid as the two terminals.

  *Electrolytic capacitors are capable of holding more charges per volume than ceramic ones.

  *Most of the electrolyte capacitors are polarized, but ceramic capacitors are never polarized.


===== Ressources =====

[[http://www.electronicsteacher.com/capacitor-chart.php|Capacitor chart]]