What are the symbols for capacitors
Capacitors are components that can store electrical charges or electrical energy.
The simplest form of a capacitor consists of two opposing metal plates. In between there is a dielectric that does not allow an electrical connection between the metal plates. The dielectric is to be understood as an insulator.
If a voltage is applied to a capacitor, an electric field is created between the two metal plates. One plate accepts positive, the other plate negative charge carriers. The distribution of the load carriers is the same on both sides.
Capacitors differ according to the type of voltage. There are DC and AC capacitors. DC capacitors are polarized. The connections must not be mixed up. AC voltage capacitors are not polarized and may be operated with both AC and DC voltage. The rms value of the nominal AC voltage must not be exceeded.
Units and symbols
Capacity has the capital C as a symbol. It is the abbreviation for the English word Capacity. The unit of measurement is the capital F for Farad. Most capacitors are given in µF, nF or pF. The most common capacities are in this range.
Farad (F) comes from the Englishman Michael Faraday, who invented the cage of the same name and from whom the electric field theory originates. He was honored by naming the capacity.
|farad||1 F.||1 F.||100 F.|
|Millifarads||1 mF||0.001 F.||10-3 F.|
|Microfarads||1 µF||0.000001 F||10-6 F.|
|Nanofarad||1 nF||0.000000001 F||10-9 F.|
|Picofarad||1 pF||0.000000000001 F||10-12 F.|
The capacity is the property of a component to store electrical energy. The capacitor is the electronic component that has this distinctive property.
The amount of charge has the symbol Q and the unit coulomb (C). The charge consists of current times time (amps times a second). The unit C of the amount of charge must not be confused with the symbol C of the capacity.
in F (C / V)
in F (As / V)
The capacity of a capacitor is determined by its structural size.
The capacity C is all the greater
- the larger the plate surface (A)
- the smaller the plate distance (d)
- the better the dipole formation in the dielectric (the greater the relative permittivity εr)
in As / Vm = F / m
Dielectric / permittivity εr
The dielectric constant is a measure of how an insulating material influences the capacitance of a capacitor. The dielectric constant εr indicates the factor by which the capacity increases if another dielectric is used instead of a vacuum. The higher the dielectric constant, the higher the capacitance or the smaller the capacitor design.
The dielectric constant indicates by how much the dielectric is better than vacuum with εr = 1.
|dielectric||εr = ε / ε0|
|Air (0 ° C, 105 Pa)||1,000576|
|Water vapor (110 ° C, 105 Pa)||1,026|
|Air (0 ° C, 107 Pa)||1,05404|
|paper||1,2 - 4|
|Glass||5 - 7|
|porcelain||4,5 - 6,5|
|Water (10 ° C)||81,1|
|Capacitor ceramic||60 - 3000|
In practice it is irrelevant whether one refers to vacuum or air. The difference is only noticeable after the decimal point.
The dielectric strength of a capacitor is related to the dielectric. It determines the highest voltage that can be applied to the capacitor. If the voltage is exceeded, the dielectric no longer insulates. A breakdown occurs through the dielectric.
A capacitor always discharges itself. The discharge is caused by the insulation, the wiring, the capacitor coating and the dielectric. The discharge is also called capacitor loss. The polarization reversal results in a high loss, especially with alternating voltage. That is why there are special AC capacitors.
The temperature coefficient TK plays an important role in filters and resonant circuits. The capacity changes depending on the temperature. The change can be positive or negative. Ideally, the capacitance does not change with a change in temperature. Some applications require a precisely calculated capacity.
Equivalent circuit diagram of a capacitor
Every capacitor sometimes has highly undesirable properties that become noticeable as parasitic effects and have a negative impact on the capacitance.
The inductance L poses a considerable dangerESL (Equivalent Series Inductivity L), which can be between 1 and 100 nH depending on the supply line and design. For example, a winding capacitor creates a not inconsiderable inductance that is now under control. At high frequencies, this inductance is uncomfortably noticeable. In the case of resonance, the capacitor becomes an LC resonant circuit (see equivalent circuit).
In the equivalent circuit diagram, the insulation resistance of the dielectric is given by R.isol (100 GΩ ... 1 TΩ) or referred to the residual current for electrolytic capacitors as R.Leak shown. This resistance ensures the self-discharge of the charged capacitor.
Then there are capacitive reactive components XC.. Together with the ohmic active component RESR (Equivalent Series Resistance) results in a complex frequency-dependent impedance Z. It is also referred to as impedance.
The ohmic components, such as connecting wires, contact resistances and the tile coverings, are contained in the resistor RESR summarized.
|paper||100 pF ... 1µF||20 %||large||large||125 ... 1000 V||No||No|
|Metal paper||0.1 ... 50 µF||20 %||large||large||160 ... 600 V||Yes||No|
|Styroflex||2 pF ... 50 nF||20 %||small||medium||50 ... 500 V||No||No|
|Metal, plastic-||0.01 ... 0.25 µF||20 %||medium||small||300 V ... 5 kV||Yes||No|
|Metal lacquer||0.1 ... 200 µF||20 %||medium||tiny||60 ... 120 V||Yes||No|
|Ceramic||0.5 pF ... 100 nF||20 %||tiny||large||250 ... 500 V||No||No|
|Electrolyte-||0.5 ... 10000 µF||-20%...+50%||large||tiny||3 ... 650 V||Yes||Yes|
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