Modern devices and circuits use a capacitor as an important electronic component. Capacitors were started to be used in electronic devices about 250 years ago. Till today, they are designed and studied for making appliances run better. There are various factors upon which the making and uses of capacitors depend.
A capacitor is a passive electrical component that stores electrical energy in the form of an electric field. Capacitance is the effect produced by the capacitor. A capacitor is made with two conductors that are separated at a distance apart with a dielectric material. The electric plates accumulate electric charge after they are connected with an active power source. One plate of the capacitor collects a positive charge, and the other collects the negative charge.
Capacitance is the ratio of electric charge to voltage. Mathematically, capacitance is represented by:
C = Q / V
Where C = capacitance in farad
Q = electric charge in coulombs
V = voltage between the plates in volts
There are various types of capacitors depending upon usage and material. Some of the major ones, which are used mostly in electronic devices, are described below.
Electrolytic capacitors have large capacities to store energy. One of the electrodes of electrolytic capacitors are made up of a thin metal layer, and the other is made up of semi-liquid electrolyte solution in the form of jelly or paste. A thin layer of oxide acts as a dielectric material that is produced electrochemically.
The size of these capacitors is very small. They are mostly polarized with the application of a DC voltage. Therefore, they are mostly used in DC power supply circuits because of their large capacitance value. In addition, they have a low voltage rating because of their polarization.
This capacitor is made up of natural minerals. The mica capacitor uses silver as a dielectric material. There are two types of mica capacitors: silver mica and clamped. Silver mica capacitors are used by filling epoxy as a coating material to the metal electrodes. Epoxy saves the silver mica from being corroded due to the harsh environment. Clamped capacitors are not used these days due to their poor capacity. Mica capacitors are used in electronic appliances that need high-temperature resistance while working along with high electrical properties. They are very stable because of their crystalline binding.
Paper capacitors are constructed using two tin foil sheets, separated at a distance apart and filled with paper, wax or oiled paper. The sheets of foils are rolled in the shape of a cylinder. Later on, they are encapsulated with plastic layering to prevent them from tearing down. After the making of the capacitor, they are connected with an external power supply.
Earlier, the paper was used as the filling material between these capacitors. These days, the paper has been replaced by plastics. The capacitance of these paper capacitors ranges from 0.001 microfarads to 2.000 microfarads. They can resist the voltage up to 2000V.
Plastics are used as a dielectric material in film capacitors. These capacitors are very thin and are made using very complex manufacturing processes. The plastic film so produced is coated with a metal layer depending upon the usage of the film capacitor. Electrodes may also be added to prevent film capacitors from corrosion.
Different materials are used to make film capacitors present in the market, such as polypropylene, polyester, metalized film, PTE, and polystyrene. Film capacitors are differentiated based on the type of material used for the dielectrics. Therefore, dielectric materials must be chosen carefully while manufacturing a film capacitor. Nevertheless, these capacitors are of low cost and are used widely due to their stability.
Non-polarized capacitors are fitted in series or parallel configurations with the power supply in AC appliances. There are two types of non-polarized capacitors: electrolytic non-polarized capacitors and plastic foil capacitors. Electrolytic capacitors are made with two capacitors placed back to back in a series configuration. This way, they produce half the capacitance than required. These capacitors are used where AC voltage is more than required.
For example, in power factor correction networks and speaker crossover filters, where large voltages are generated, these non-polarized capacitors are used to produce half capacitance to save the appliance.
In ceramic capacitors, ceramic is used as a dielectric material. Ceramic was one of the first materials to be used as a dielectric material. Various shapes are used to make ceramic capacitors: tubular, circular, barrier-type, etc. Barrier-type ceramic capacitors are obsolete nowadays.
The two common types of ceramic capacitors used these days are ceramic disc capacitors and multilayer ceramic capacitors. The discs of the ceramic disc capacitor are coated with silver to produce large capacitance. These will have high-frequency responses because of parasitic effects like inductance and resistance. In contrast, multilayer ceramic capacitors are used widely because they are smaller and range between 1nF to 1µF.