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A Capacitor is a passive two-terminal electrical device consisting of two or more conducting plates separated from one another by insulating material and used for storing an electric charge, capacitors are originally known as a condenser. Aside from storing energy, a capacitor can also block the flow of direct current and permit the flow of alternating current and it can work to smooth out voltage fluctuations.
Electrical energy is stored in the capacitor between the conducting plates, with the external circuitry serving as the control mechanism for releasing the energy at the predetermined rate and time. Whatever the physical construction of the device, the amount of electric charge in coulombs (q) on the capacitor is directly proportional to the potential difference in volts (V) between plates.
Capacitance (C) is the ability to store electrical charge, either with static electricity or by an electric current exhibits capacitance. Thus Capacitance is the measure of electric charge that can be stored per unit of voltage differential between the metallic conductors. The capacitance of a capacitor also depends on the size of the plates, their closeness together, and the nature of the material between them. In other words, it is directly proportional to the area of the plates and inversely proportional to the spacing between the two plates.
The unit of the capacitance is the “Farad” but because it is too large a unit for practical work, the MicroFarad (uF, one millionth of a Farad) and the Picofarad (pF, one millionth of a microfarad) are used. The higher the value, the more electrons the capacitor can store at any one time.
SOME APPLICATION OF A CAPACITOR:
BLOCKING DC VOLTAGES – The passage of direct current can be blocked by capacitor. When this happen, a circuit designer can isolate a circuit element from a dc supply. In this application, there is a choice of dielectric, each of which will allow a certain amount of leakage current caused by a random passage of electrons through or around the dielectric.
COUPLING AND DECOUPLING – capacitor block direct current and they also seem to pass alternating current. Capacitor is charged and then discharged of current as the AC voltage alternates from one section of the circuit to another or different circuits.
BYPASSING – As both blocking and coupling functions are simultaneously done, a capacitor can separate the dc and ac components of a mixed signal. To do a bypass function, the capacitor is put in parallel with the circuit element to assure that the dc portion does not appear on the circuit element.
FREQUENCY DISCRIMINATION – the capacitor in this function is, as in coupling function, employed to discriminate between signals. It should be recalled that the higher the capacitors capacitance value, the greater the current will be at any given frequency and that for a given capacitance, the higher the frequency, the more the frequency, the more current will be passed.
TIMING – The rate of charge that flows in and out of a capacitor is directly related to the capacitance (C) and the series of resistance (R) of the circuit. Thus, the selected R and C combination, otherwise known as time constant, determines the timing or speed of response of a circuit. On application can be seen in the time-delay relay.
SMOOTHING OUT VOLTAGES – Considering that unregulated power supplies are subject to transient peak and voltage surges (which can be damaging to the circuit components), capacitors are equipped with the ability to absorb these said peaks and pass on a steady voltage to a circuit. It is widely used to clean up voltage.
ENERGY STORAGE – capacitors can also be used to accumulate electrical energy from a low energy source over a long period of time. This is done by discharging the stored energy rapidly, allowing high current to perform tasks such as heating, welding or firing photoflash bulbs.
ARC SUPPRESSION – To reduce or eliminate interference caused by the rapid opening or closing of circuits (switches and relays), capacitor-resistor and capacitor-inductor combinations are used. Such arching resulting from interrupting the current flow by such circuit radiate signal in the form of noise which can interfere with any broadcast reception. The capacitor can also prolong the life of the contacts of the switches and relays.
CAPACITOR WORKING VOLTAGE:
The working voltage or WV of a capacitor, is the maximum voltage that a capacitor can withstand before the dielectric layers in the component become damaged. At higher voltages, the current may simply arc between the plates. If a capacitor is inserted in a circuit with a higher input voltage than the indicated working voltage of the capacitor a spark may develop within the capacitor and punches through the dielectric material, leaving the component useless or shorted. As always it is a good idea to select a capacitor with a working voltage greater than the voltage in the circuit for safety.
TYPES OF CAPACITOR
he plate material in a ceramic capacitor is a silver compound that is fixed or deposited upon the surface of a dielectric. The dielectric is a ceramic form made of tantanium dioxide or a silicate compound which can be of disk or tabular shape. The overall capacitor assembly is coated with plastic material. Ceramic capacitor have a high dielectric constant that provides them with high working voltage ratings. That capacitance of these capacitors varies from 1 pF to 0.1 uF. They have a wider applications like filtering, coupling and decoupling, resonant circuit parameter and others.
PAPER CAPACITOR – It’s plates are made of aluminum or tin foil with a dielectric of paper that is impregnated (saturated) with an oil or wax compound. Such capacitors are non-polarized devices. Their capacitance range from 0.001 to 1 uf and their temperature coefficient is comparatively higher than those of the other types.
PLASTIC FILM CAPACITOR :These capacitors are manufactured from plastic films usually of the oriented crystalline type. The plastics used are thermoplastic films that have been extruded, stretched and heat treated. Moister has a little effect on the plastic films dielectric properties. This fact makes make the packaging of plastic film capacitors easier compared with other types. The electrical characteristics of these capacitors relate to the manufacturing process. There are 3 general classes of plastic film capacitors – polystyrene, polyester, and polycarbonates.
MICA CAPACITOR –several strips of metal foil, either aluminum, tin or copper, are sandwiched between thin sheets of mica which serve as the dielectric materials. Alternate strips of foil are connected to form the plate. These capacitors are found in the range of 1pF to 0.01 uF in capacitance and have a stable temperature coefficient characteristic. Its useful applications are in high frequency circuit.
ELECTROLYTIC CAPACITOR – These are capacitors whose dielectric layers are formed by an electrolytic method, and need not contain an electrolyte. The most common electrolytic capacitors are the aluminum electrolytic capacitors and tantalum electrolytic capacitors.
ALUMINUM ELECTROLYTIC CAPACITORS: consist of etched foils ( the anode and cathode foils) and paper separators rolled into a tabular form. During the assembly process, thin coating of aluminum oxide is deposited upon the surface of the anode foil and this coating becomes the dielectric material of the capacitor. The thickness of the oxide determines the working voltage rate of the capacitor which generally does not exceed 500volts.
TANTALUM ELECTROLYTIC CAPACITORS: Tantalum Capacitoruse tantalum metal foils and acid electrolytes. The oxide coating deposited upon the surface of their foils has greater dielectric constant than that of aluminum oxide. These capacitors are more rugged and have high temperature coefficient. However, their working voltage ratings are much lower compared with the first. Take note that both types of electrolytic are polarized devices that must be operated under Direct Current (DC) voltage condition. Their application ranges from consumer to entertainment.
VARIABLE CAPACITOR: This capacitor are also known as air dielectric variable (or tuning) capacitor. It consists of stationary plates (stator) and a set of a position that allows them to mesh with each other without touching. By rotating the shaft of this capacitor, the surface area directly opposite the stator plates varies, causing the capacitance to vary.