The basic principles and specifications Capacitors

The basic principles and specifications Capacitors

Capacitors are electronic components that can store electrical charges. The structure of a capacitor made of 2 pieces of metal plates separated by a dielectric material. Dielectric materials are commonly known as air vacuum, ceramic, glass and others. If both ends of the metal plate was given voltage, the positive charges will accumulate on one leg (electrode) metal and at the same time the negative charges accumulated on the metal edges of one another. The positive charge can not flow toward the negative pole and the opposite end of the negative charge can not be heading back up the positive pole, because the dielectric material separated by a non-conductive. Electric charge is "stored" as long as no conduction at the ends of the legs. In the wild, this phenomenon occurs when the capacitor charge accumulation-positive and negative charges in the clouds.

Capacitance

Capacitance is defined as the ability of a capacitor to hold charge of the electron. Coulombs in the 18th calculate that 1 coulomb = 6.25 x 1018 electrons. Then Michael Faraday made postulate that a capacitor will have a capacitance of 1 farad when a voltage 1 volt can load as many as 1 electron charge coulombs. With the formula can be written:

Q = CV ... ... ... ... .... (1)

Q = electron charge in C (coulombs)

C = the capacitance in F (farads)

V = the voltage in V (volts)

In practice the manufacture of capacitors, capacitance is calculated by knowing the area of ​​metal plate (A), distance (t) between the second metal plate (dielectric thickness) and a constant (k) dielectric material. With the formulation can be written as follows:

C = (8.85 x 10-12) (k A / t) ... (2)


Here is a sample table constants (k) of some simplified dielectric material.
Air vacuum k = 1
Aluminum oxide is k = 8
Ceramic k = 100 - 1000
Glass k = 8
Polyethylene k = 3

For the series of practical electronics, the unit of farads is very huge. Generally, the capacitor that is in the market has units of UF (10-6 M), nF (10-9 M) and pF (10-12 F). Conversion unit is important for ease of reading the amount of a capacitor. For example 0.047uF can also be read as a 47nF, 0.1nF same or another example with 100pF.


Capacitor Type

The capacitor consists of several types, depending on the dielectric material. For more simple can be divided into 3 parts, namely electrostatic capacitors, electrolytic and electrochemical.

Electrostatic Capacitor

Electrostatic capacitors are a group of capacitors that are made with a dielectric material of ceramic, film and mica. Ceramic and mica is a popular material and cheap to make small capacitance capacitors. Quantities available from pF to several UF, which is usually for a series of applications relating to high frequency. Groups including the dielectric film material is a material such as polyester (polyethylene terephthalate, or known as Mylar), polystyrene, polyprophylene, polycarbonate, metalized paper and others.

Mylar, MSM, MKT are some examples of the trademark name for the capacitor with a dielectric material film. Generally this group of capacitors is the non-polar.

Electrolytic Capacitors

Electrolytic capacitor group consisting of the capacitors dielectric materials are metal-oxide layer. Generally capacitor including this group is a polar capacitor with the + and - in the body. Why are these capacitors can have a polarity, is due to the manufacturing process uses electrolysis to form the positive pole anode and cathode negative pole.

It has long been known for some metals such as tantalum, aluminum, magnesium, titanium, niobium, zirconium and zinc (zinc) surface can be oxidized to form metal-oxide layer (oxide film). Oxidation layer is formed through a process of electrolysis, as in the process of gold plating. Metal electrode is dipped into the solution electrolit (sodium borate) and given a positive voltage (anode) and the solution given electrolit negative voltage (cathode). Oxygen in electrolyte solution apart and oxidize metal plate surface. For example, if used Aluminum, it will form a layer of aluminum-oxide (Al2O3) on the surface.

Thus successive metal plate (anode), layer-metal-oxide and the electrolyte (cathode) form a capacitor. In this layer-metal-oxide as the dielectric. From formula (2) great unknown capacitance is inversely proportional to dielectric thickness. Metal-oxide layer is very thin, and thus can be made large enough capacitance capacitors.

Due to economical and practical reasons, generally a lot of metal material used is aluminum and tantalum. The material most widely and cheaply is Aluminium. To get a broad surface, Aluminum plate material is usually rolled radially. So in a way that can be obtained large capacitance capacitors. For example 100uF, 470uF, 4700uF and others, which often also called capacitor elco.


Tantalum capacitor electrolyte material in a liquid there but there is also a solid. Called the solid electrolyte, but it is not the solution electrolit its negative electrode, but other materials are manganese-dioxide. Thus this type of capacitors can have large capacitance, but becoming more slender and petite. Also because of all the solid, then their work time (lifetime) to be more durable. Capacitors of this type also has a very small leakage current can be understood why so Tantalum capacitors become relatively expensive.


Electrochemical Capacitors

One other type of capacitor is an electrochemical capacitor. Including this type of capacitors and batteries are the batteries. In fact the battery and capacitor batteries is very good, because it has a large capacitance and leakage current (leakage current) is very small. This type of capacitors of this type are also still in development to get a large capacitance, but small and light, for example for electric cars and mobile application provider.


Reading Capacitance

In a large capacitor, the capacitance is generally written with sheer numbers. Complete with a maximum voltage value and polarity. For example, the capacitor capacitance elco clearly written for 22uF/25v.

Capacitors are tiny and small physical size is usually only read 2 (two) or 3 (three) numbers only. If there are only two digits unit is pF (pico farads). For example, a capacitor that reads two digits 47, then the capacitance is 47 pF capacitor.

If there are 3 digits, the first and second digits indicate the nominal value, while the 3rd digit is multiplier. Multipliers in accordance with nominal rates, respectively 1 = 10, 2 = 100, 3 = 1.000, 4 = 10,000 and so on. For example on ceramic capacitors written 104, the capacitance is 10 x 10,000 = 100.000pF or = 100nF. Another example of such a written 222, meaning that the capacitance of the capacitor is 22 x 100 = 2200 pF = 2.2 nF.


Working voltage (working voltage)

Working voltage is the maximum allowable voltage so that the capacitor can still work well. The electro-mania may have had capacitors that exploded due to excess voltage. For example 10uF 25V capacitor, the voltage that can be given should not exceed 25 volts dc. Generally, polar capacitors work on DC voltage and non-polar capacitor works on AC voltage.

Tolerance

As with other components, there are large nominal capacitance tolerance. The above table presents the values ​​of tolerance with codes specific numbers or letters. With the above table the user can easily know the tolerance of capacitors which usually accompany the printed face value capacitors. For example, if a written 104 X7R, then capacity is 100nF with a tolerance of + / -15%. Simultaneously dikethaui also recommended that the working temperature is between-55Co to +125 Co. (see table characteristic code)

Insulation Resistance (IR)

Although the dielectric material is a material non-conductors, but there is still a current that can pass through. That is, dielectric material also has a resistance. although its value is immense. This phenomenon is called leakage current DCL (DC Leakage Current) and the dielectric resistance is called Insulation Resistance (IR). To explain this, here is the series capacitor model.

If not given the expense, should the capacitor can store charge in perpetuity. But from the above model, known to exist resitansi dielectric IR (Insulation Resistance) is parallel to the capacitor. Insulation resistance (IR) is very large (MOhm). Consequently, of course, leakage current (DCL) is very small (UA). To obtain a large capacitance is required electrode surface area, but this will cause the smaller the dielectric resistance. Because of the IR is always inversely proportional to the capacitance (C), the characteristics of the dielectric resistance is usually also served with the amount of RC (IR x C) that its unit megaohm ohm-farads or micro-farads.