Capacitors play an important role in circuits such as tuning, bypassing, coupling, and filtering. It is used in the tuning circuits of transistor radios and in the coupling and bypass circuits of color televisions.
With the rapid change of electronic information technology, digital electronic products are updated more and more quickly to flat-panel TV (LCD and PDP), notebook computers, digital cameras and other products based on the production and sales of consumer electronics products continue to grow, driven by the growth of the capacitor industry.
Introduction Editor
Capacitors are components that store electricity and electrical energy (potential energy). A conductor surrounded by another conductor, or a conductor in which all the electric field lines emitted by one conductor terminate in the other conductor, is called a capacitor.
The formula for the capacitance of a parallel-plate capacitor:
Where UA-UB is the potential difference between the two parallel plates, εr is the relative dielectric constant, k is the electrostatic force constant, S is the area directly opposite the two plates, and d is the distance between the two plates. Note: The electric field in a parallel plate capacitor is a uniform electric field. [3]
Capacitance is different from capacitance. Capacitance is a fundamental physical quantity with the symbol C and the unit F (farad). [3]
General formula C = Q / U, parallel plate capacitor special formula: the electric field strength between the plates E = U/d. [3]
Capacitor main parameters edit
(1) nominal capacitance, for the sign on the capacitor capacity. However, the actual capacitance of the capacitor and
Capacitor charging process
Capacitor charging process
Nominal capacitance is a deviation from the accuracy of the level of correspondence with the allowable error. General capacitors commonly used Ⅰ, Ⅱ, Ⅲ level, electrolytic capacitors with Ⅳ, Ⅴ, Ⅵ level indicates the capacity accuracy, according to the use of selection. The capacitance value of electrolytic capacitors depends on the impedance presented when working under AC voltage, and the capacitance value will change with the change of working frequency, temperature, voltage and measurement method. The unit of capacitance is F (law). [4]
Capacitors, since they are a "container" for storing charge, have a "capacity" size. In order to measure the ability of a capacitor to store charge, the physical quantity of capacitance is determined. Capacitors must be under the action of an applied voltage in order to store charge. Different capacitors may not store the same amount of charge under voltage. Internationally standardized, to the capacitor applied 1 volt DC voltage, it can store the amount of charge, for the capacitor's capacitance (that is, the amount of electricity per unit voltage), with the letter C said. The basic unit of capacitance is the farad (F). In 1 volt dc voltage, if the capacitor stored charge for 1 coulomb, the capacitance is set at 1 farad, farad with the symbol F, 1F = 1Q/V. In practice, the capacitance of the capacitor is often much smaller than 1 farad, commonly used smaller units such as millifarads (mF), microfarads (μF), nano-farads (nF), pico-farads (pF), and so on, the relationship between: 1 microfarads equal to millionth of a farad; 1 picofarad is equal to one millionth of a microfarad, i.e.: [5]
1 farad (F)=1000 millifarad (mF); 1 millifarad (mF)=1000 microfarad (μF); 1 microfarad (μF)=1000 nanofarad (nF); 1 nano-farad (nF)=1000 picofarad (pF); i.e.: 1F=1,000,000 μF; 1 μF= 1000000pF. [5]
(2) Rated voltage, for the highest DC voltage that can be continuously added to the capacitor at the lowest ambient temperature and rated ambient temperature. If the operating voltage exceeds the capacitor's withstand voltage, the capacitor will be punctured, causing damage. In practice, the withstand voltage value will become lower as the temperature increases. [4]
(3) Insulation resistance. DC voltage applied to the capacitor, resulting in leakage current, the ratio of the two is called insulation resistance. When the capacitance is small, its value depends mainly on the surface state of the capacitor; capacity greater than 0.1μF, its value depends mainly on the medium. Usually, the larger the insulation resistance, the better. [4]
(4) Loss. Capacitor under the action of electric field, in the unit time due to the heat consumed by the energy is called loss. The loss is related to the frequency range, dielectric, conductance, and resistance of the metallic part of the capacitor. [4]
(5) frequency characteristics. As the frequency rises, the capacitance of a general capacitor shows a decreasing pattern. When the capacitor works below the resonant frequency, the performance of capacitive; when more than its resonant frequency, the performance of inductive, then it is not a capacitor but an inductor. So we must avoid capacitors working above the resonance frequency. [4]
Role editing
Capacitor
Capacitor
In a DC circuit, a capacitor is the equivalent of a circuit breaker. A capacitor is a component capable of storing an electrical charge and is one of the most commonly used electronic components. [6]
This starts with the construction of a capacitor. In its simplest form, a capacitor consists of pole plates at each end and an insulating dielectric (including air) in the center. When energized, the pole plates are charged, creating a voltage (potential difference), but because of the insulating substance in the middle, the entire capacitor is non-conductive. However, such a situation is under the precondition that the critical voltage (breakdown voltage) of the capacitor is not exceeded. We know that any substance is relatively insulating, when the voltage at the ends of the substance is increased to a certain level, the substance is conductive, and we call this voltage the breakdown voltage. Capacitors are no exception, capacitors are not insulators when they are broken down. At the middle school level, though, such voltages are not seen in circuits, so they all work below the breakdown voltage and can be looked at as insulators. [6]
But in an AC circuit, because the direction of the current changes as a function of time. And the process of charging and discharging a capacitor has a time, and at this time, a varying electric field is formed between the plates, and this field also varies as a function of time. In effect, current passes between the capacitors in the form of an electric field. [6]
The role of capacitors:
●Coupling: capacitors used in coupled circuits are called coupling capacitors, which are used in a large number of resistive-capacitive coupled amplifiers and other capacitively coupled circuits to isolate the current from the AC. [6]
●Filtering: Capacitors used in filtering circuits are called filter capacitors, and are used in power supply filtering and various filter circuits, where the filter capacitor removes signals in a certain frequency band from the total signal. [6]
●Decoupling: Capacitors used in decoupling circuits are called decoupling capacitors, and these capacitor circuits are used in DC voltage supply circuits for multistage amplifiers, where the decoupling capacitor eliminates harmful low-frequency cross-connections between each stage of the amplifier. [6]
●High-frequency cancellation: Capacitors used in high-frequency cancellation circuits are called high-frequency cancellation capacitors, and are used in audio negative feedback amplifiers in order to cancel possible high-frequency self-excitation, using such capacitor circuits to cancel possible high-frequency whistling of the amplifier. [6]
●Resonance: A capacitor used in an LC resonant circuit is called a resonant capacitor, and this capacitor circuit is required in both LC parallel and series resonant circuits. [6]
●Bypass: Capacitors used in bypass circuits are called bypass capacitors, and bypass capacitor circuits can be used in circuits where a certain band of signals needs to be removed from a signal, depending on the frequency of the signal removed, there are full-frequency domain (all AC signals) bypass capacitor circuits and high-frequency bypass capacitor circuits. [6]
●Neutralization: A capacitor used in a neutralization circuit is called a neutralization capacitor. Such neutralizing capacitor circuits are used in radio high-frequency and intermediate-frequency amplifiers, and television high-frequency amplifiers to eliminate self-excitation. [6]
●Timing: Capacitors used in timing circuits are called timing capacitors. Timing capacitor circuits are used in circuits that require time control by charging and discharging capacitors, which act to control the magnitude of the time constant. [6]
●Integral: A capacitor used in an integral circuit is called an integral capacitor. This integral capacitor circuit is used in synchronous separation circuits for potential field scanning to remove the field synchronization signal from the field composite synchronization signal. [6]
●Differential: A capacitor used in a differential circuit is called a differential capacitor. This differential capacitor circuit is used in trigger circuits in order to get a spike trigger signal to get a spike pulse trigger signal from various types of (mainly rectangular pulse) signals. [6]
●Compensation: A capacitor used in a compensation circuit is called a compensation capacitor, and this low-frequency compensation capacitor circuit is used in the bass compensation circuit of a cassette deck in order to boost the low-frequency signal in the playback signal, and in addition, there is a high-frequency compensation capacitor circuit. [6]
●Bootstrap: A capacitor used in a bootstrap circuit is called a bootstrap capacitor, and this bootstrap capacitor circuit is used in the output stage circuit of a commonly used OTL power amplifier to boost the amplitude of the signal's positive half-circle by a small amount by means of positive feedback. [6]
●Crossover: A capacitor in a crossover circuit is called a crossover capacitor, and crossover capacitor circuits are used in speaker crossover circuits in speakers to enable high-frequency speakers to operate in the high-frequency band, mid-frequency speakers to operate in the mid-frequency band, and low-frequency speakers to operate in the low-frequency band. [6]
●Load capacitance: The effective external capacitance that determines the resonant frequency of the load along with the quartz crystal resonator. The standard values of load capacitance are 16pF, 20pF, 30pF, 50pF, and 100pF. The load capacitance can be adjusted according to the specific situation, and by adjusting it, you can generally adjust the operating frequency of the resonator to the nominal value.