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notes/Resources/electricity/passive-components/capacitors.md
2022-04-15 14:51:51 +02:00

2.1 KiB

Capacitors

Capacity is measured in Resources/electricity/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