98 lines
2.1 KiB
Markdown
98 lines
2.1 KiB
Markdown
# Capacitors
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Capacity is measured in [[glossary#Farad|Farads]].
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Capacity is calculated as follows:
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$$
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\begin{flalign}
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& C = \epsilon r \frac{A}{4\pi d} &&\\\
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\\
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& \epsilon r = \text{Dielectrics relative permittivity} &&\\
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& A = \text{Amount of Area the plates overlap} &&\\
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& d = \text{Distance between plates} &&\\
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\end{flalign}
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$$
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### Important Metrics
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**Size**
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Larger Capacity $\approx$ Larger Size
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**Charge**
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How much charge a capacitor is currently storing depends on the potential difference between its plates
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$$
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\begin{flalign}
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&Q = C*V &&\\\
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\\
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&Q = Charge \\
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&C = \textit{Capacitance (Constant Value)}\\
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&V = Voltage\\
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\end{flalign}
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$$
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**Voltage**
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The current that is flowing through a capacitor is the derivative of voltage
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**Charging Current**
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The charging current through a capacitor is proportional to the rate of change in voltage through it.
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The formular for calculating the current flowing through a capacitor is following
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*Note: only for linearly rising/falling voltages (not AC)*
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$$
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i = C\frac{dv}{dt}
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$$
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**Capacitance**
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The amount of charge a capacitor can store
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**Maximum Voltage**
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Each capacitor has a maximum voltage that can be dropped across it.
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**Leakage Current**
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Capacitors are not perfect, and leak some current across the terminals.
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**Equivalent series Resistance (ESR)**
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The terminals are not 100% conductive, so the will have some very small resistance, (usually less than $0.01\ohm$)
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**Tolerance**
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The capacity is not always exact, the tolerance describes how much it could vary, usually about $\mp 1\%$ to $\mp 20\%$
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## Ceramic Capacitors
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- least expansive
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- relative small usually $< 10\micro F$
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- low current leakage and ESR
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- best for high frequency coupling
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## Aluminium and Tantalum Electrolytic
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- Usually polarized
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- Capacity usuially $1\micro F - 1mF$
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- Good for high voltage
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## Super Capacitors
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- Usually can handle only low voltage
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- Capacity in the range of farads
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## Film Capacitor
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- usually low ESR
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## Mica Capacitor
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- Can work in hot environments > $200\deg$
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- Low ESR
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- High Precision
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- High Cost
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