Capacitors

Capacity is measured in glossary#Farad.

Capacity is calculated as follows:


\begin{flalign}
& C = \epsilon r \frac{A}{4\pi d} &&\\\
\\
& \epsilon r = \text{Dielectrics relative permittivity} &&\\
& A = \text{Amount of Area the plates overlap} &&\\
& d = \text{Distance between plates} &&\\
\end{flalign}

Important Metrics

Size Larger Capacity \approx Larger Size

Charge How much charge a capacitor is currently storing depends on the potential difference between its plates


\begin{flalign}
&Q = C*V &&\\\
\\
&Q = Charge \\
&C = \textit{Capacitance (Constant Value)}\\
&V = Voltage\\
\end{flalign}

Voltage The current that is flowing through a capacitor is the derivative of voltage

Charging Current

The charging current through a capacitor is proportional to the rate of change in voltage through it.

The formular for calculating the current flowing through a capacitor is following

Note: only for linearly rising/falling voltages (not AC)


i = C\frac{dv}{dt}

Capacitance The amount of charge a capacitor can store

Maximum Voltage Each capacitor has a maximum voltage that can be dropped across it.

Leakage Current Capacitors are not perfect, and leak some current across the terminals.

Equivalent series Resistance (ESR) The terminals are not 100% conductive, so the will have some very small resistance, (usually less than 0.01\ohm)

Tolerance The capacity is not always exact, the tolerance describes how much it could vary, usually about \mp 1\% to \mp 20\%

Ceramic Capacitors

least expansive
relative small usually < 10\micro F
low current leakage and ESR
best for high frequency coupling

Aluminium and Tantalum Electrolytic

Usually polarized
Capacity usuially 1\micro F - 1mF
Good for high voltage

Super Capacitors

Usually can handle only low voltage
Capacity in the range of farads

Film Capacitor

usually low ESR

Mica Capacitor

Can work in hot environments > 200\deg
Low ESR
High Precision
High Cost

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