What is a capacitor and its role?

Last Update Time: 2018-12-13 15:47:12

1.All kinds of capacitors are used in the electronic production, and they play different roles in the circuit. A capacitor is a container for storing charges. In theory, the capacitor has no loss to the electric energy, and the capacitor is  very common element in the electronic circuit. The capacitor is one of the most commonly used electronic components. Its general character symbol is represented by " C ".

The basic structure and symbols of the electrodeless fixed capacitor

It is mainly composed of metal electrode, dielectric layer and lead wire. Since there is an insulating dielectric layer between the two metal electrodes, the two electrodes are mutually insulated. This structural characteristic determines that the capacitor has the basic performance of " DC blocking communication ".


The  electrolytic capacitor inner part is composed of a metal electrode and an electrolyte. The polarity and voltage magnitude of the direct current are certain, so the capacitor can not be passed the polarity of alternating current and the magnitude of voltage are constantly changing, enabling the capacitor to continuously charge and discharge, forming a charging and discharging current, it is shown that the AC can be charge-discharge characteristic of the capacitor.


2.The main performance parameters of the capacitor

The capacitor has a lot of performance parameters. Here are some common parameters:


 (1) capacitance is the ability of a capacitor to store charges. Usually, the charge stored in the capacitor plus the 1V DC voltage is called the capacitance of the capacitor. The basic unit is Farah (f). The Farah unit is too large (not commonly used) because the capacity of the capacitor is usually much smaller than the capacity of 1 Fala, so the micromethod (uF) and NF (NF) are usually used, PF (PF) .

 The relation is: 1F = 1000000 micromethod F= 1000000000 nF = 1000000000000PF


 (2) voltage withstand voltage Refers to the maximum DC voltage of capacitors in a circuit for a long time, which can be sustained without breakdown. For components with the same structure, medium and capacity, the greater the pressure, the larger the volume. In the AC circuit, the voltage value of the capacitor should be greater than the peak value of the circuit voltage, otherwise it may be breakdown, and the size of the pressure is related to the dielectric material. When the voltage across the capacitor exceeds the rated voltage, the capacitor will be broken down. The voltage divider of general electrolytic capacitor is 6.3V, 10V, 16V, 25V, 50V, 160V, 250V, etc.

( 3 ) The maximum deviation range allowed by the actual capacitance and the nominal capacitance is the error. The errors are generally classified into level-3, level-1, 5 %, level-1, 10 %, and 20 %. In some cases, there is zero, which is less than 2 %. The allowable error of the precision capacitor is small, and the error of the electrolytic capacitor is large, and they adopt different error grades.

 ( 4 ) Insulation resistance insulated electric Yang is used to indicate the size of leakage. A capacitor with a small capacity, the insulation resistance is very large, in a few hundred megabytes or gigabytes of ohms. The insulation resistance of the electrolytic capacitor is generally small. Relatively speaking, the greater the insulation resistance, the better, the leakage is also small.

( 5 ) The temperature coefficient of temperature coefficient is within the range of-constant temperature, and the relative change value of capacitance is 1C per change of temperature. The smaller the temperature coefficient, the better.

( 6 ) capacitive reactance refers to the ability of a capacitor to block alternating current, the unit of which is Ω, which is indicated by Xc. Xc = 1 / 2 nfc. Among them, Xc, f frequency, unit hertz ( Hz ), c capacity, unit farad ( F ). The higher the frequency, the greater the capacity, the smaller the capacitive reactance.


3.The capacitance marking method of the capacitor is as follows.

( 1 ) Direct annotation method is to use numbers and letters to mark the specifications and models directly on the outer shell, which is mainly used on the larger capacitor . It is usually used to label capacity, pressure, error, temperature range and so on; and the letters are used to indicate the media materials, packaging forms and so on. The letter is usually divided into four parts, the first letter is usually fixed to C, indicating the capacitance; the second letter represents the dielectric material.

In some manufacturers, the " 0 " of an integer unit is often omitted, for example, in the direct marking method. 056F " means 0.056 pF; some use R to denote the decimal point, such as R47F, which means 0.47F.

( 2 ) The method of literal symbols is used to mark the main parameters of the capacitor by means of a combination of letters or numbers or both digital representation is usually represented by three digits, the first two represent valid numbers, and the third represents the number of valid digits multiplied by the screen times of 10, the unit is pF, such as " 202 " means 200pF.," 225 " means 200000 pF

When the word is " 9 ", the meaning is 1/10, and 569 indicates that 56X10-1pF = 5.6pF.

( 3 ) The color mark of the color ring is similar to the resistance of the capacitor, the unit is generally pF. For the coil or rectangular sheet and other capacitance, the first ring of the non-lead end is the first the color ring is followed by the second color ring, the third color ring, and the color ring capacitance is also divided into four or five rings, the far fifth or sixth ring, which often represent the capacitance characteristics or operating Voltage. The first, the second ( 3, 5 color ring ) ring is the effective number, and the third ( 4, 5 color ring ) ring is the number of " 0 " added behind, and the fourth ( 5.5 color ring ) ring is the error, the value of each color ring and the color ring resistance sample unit are P. In addition, if the width of a color ring is 2 or 3 times the width of the standard width, it means that it is 2 or 3 color rings of the same color.