Capacitor

Capacitor – a fundamental passive electronic component (next to Inductor and Resistor), which is made of at least two electrical conductors (plates) and a dielectric separating them (the insulator).  After applying voltage to the plates, the gathering of the electric charge begins.
Depending on the construction, parameters and the type of system in which capacitors are applied, they can collect energy, engage (energy transfer), filter and block the signals. Filters and RC timers took its name from the combination of Resistor and Capacitor in one single system – and similarly in the RLC system Resistor and Capacitor were used but with the addition of the Coil.

Fig. 1. Capacitor Symbol

The capacity of a capacitor (the amount of charge that capacitor can store) is expressed in Farads [F]. Despite the fact that 1 Farad is a large unit, the commonly produced capacitors are with capacitance values of pico [pF], nano [nF] and micro [µF] farads.

C – capacitance of the capacitor [F – Farad]
Q – electric charge on one plate [C–Coulomb]
V– voltage between plates [V–Volt]

Capacitors – Division

• electrolytic – they operate only at low frequencies, have considerable capacity and the amount of leakage,
• ceramic – usually operate at high frequencies, trimmers, which are variable-capacitance capacitors, are also made of this material,
• polymer – (plastic) – they are suitable for the operation at high currents and characterized by high voltage resistance.

Capacitor – Main technical parameters

• Rated capacity – the value provided by the manufacturer, it determines the capacity of this element,
• Capacitance tolerance – it’s given in percentage [%], the maximum deviation of the actual value of the item from its nominal value,
• Rated voltage – the maximum permisible voltage value for the corresponding component, it’s generally given as the sum of the voltage and the peak value of the alternating voltage,
• Test voltage – the voltage value that the capacitor is able to “withstand” in a short time,
• Temperature coefficient of capacitance (TCC)- it describes the maximum change in capacitance in the given range of temperatures,
• Leakage – responsible for self-discharge of the capacitor, dependent on the insulation resistance,
• Resistance to voltage pulses – described the optimal frequency of charging and discharging the capacitor,
• Capacitor dissipation factor (tan δ) – it is dependent from the temperature and frequency, the higher value, the worse quality of the capacitor.

Capacitors – Series and Parallel connections

As it is in the case of both inductors and resistors, capacitors can be connected in parallel and in series.

Series connection:

Fig. 2.Capacitors connected in series

Capacity of capacitors connected in series (unlike the resistors) can be described by the following formula:

Parallel connection

Capacitance of capacitors connected in parallel are given by the formula:

The electric charge of capacitors connected in parallel are the sum of the charges gathered on them – as the relation above indicates.

Fig. 3. Capacitor Parallel Connection