A capacitor is an electronic component used to store electrical charge. It is separated by an insulating medium between two conductors, creating an electric field. When a voltage is applied across a capacitor, charge builds up in the electric field between the conductors, causing the capacitor to accumulate charge.

 

Charges will move under force in the electric field. When there is a medium between conductors, it will hinder the movement of charges and make charges accumulate on the conductors, resulting in the accumulation and storage of charges. The amount of stored charges is called capacitance.

 

Capacitance refers to the ability to hold an electric charge. Any electrostatic field is composed of many capacitors, where there is an electrostatic field, there is a capacitance, and the capacitance is described by the electrostatic field.

 

Capacitance is a physical quantity that expresses the ability of a capacitor to hold charges. Physically speaking, capacitance is a static charge storage medium, and the charge may exist permanently. This is its characteristic, and it has a wide range of uses. It is an indispensable electronic component in the field of electronics and electricity.

 

The ratio of the amount Q carried by the capacitor to the voltage U between the two poles of the capacitor is called the capacitance of the capacitor. In circuitry, given a potential difference, the ability of a capacitor to store charge, called capacitance, is denoted as C. Using the International System of Units, the unit of capacitance is farad, marked as F.

 

Ⅰ. The basic principle of capacitance

 

The basic principle of capacitance is to store charge based on the electric field between two conductors. When a capacitor is connected to a power source and a voltage is applied, an electric field is formed inside the capacitor.

 

A capacitor consists of two metal conductors, usually parallel metal plates, separated by an insulating material. The terminals where the conductors are connected to the power source are called the plates of the capacitor. Insulating materials prevent the direct flow of charge between conductors, but allow electric fields to pass.

 

When a voltage is applied from a power source, i.e. a voltage difference is applied between the two plates of a capacitor, an electric field develops in the insulating material. An electric field causes free electrons on a conductor to move and accumulate charge on the surface of the conductor. A positive charge builds up on one plate and a negative charge builds up on the other plate.

 

Capacitors slowly discharge when power is disconnected or when the capacitor is connected to other components. Charges in the electric field will start to flow until the charges on the two plates are completely released. This process is called discharging the capacitor.

 

Ⅱ. Capacitance calculation formula

For a capacitor, if the potential difference between the two stages is 1 volt with 1 bank of electricity, the capacitance of this capacitor is 1F, that is: C=Q/U. But the size of the capacitance is not determined by Q (charged quantity) or U (voltage), that is, the formula for determining the capacitance is: C=εrS/4πkd. Among them, εr is the relative permittivity, S is the facing area of the capacitor plate, d is the distance of the capacitor plate, and k is the electrostatic force constant. Common parallel plate capacitors have a capacitance of C=εS/d (ε is the dielectric constant of the medium between the plates, ε=εrε0, ε0=1/4πk, S is the area of the plates, and d is the distance between the plates).

 

Definition formula:

 

Ⅲ. Types of Capacitors

 

1.Electrolytic Capacitor: An electrolytic capacitor uses an electrolyte as a dielectric, which contains an electrolyte. They usually have very high capacitance values and are suitable for applications requiring large capacitance, such as power supply filtering and coupling capacitors. Electrolytic capacitors have polarity and need to be connected correctly to avoid damage.

 

2.Variable Capacitor: Tuning capacitors have the characteristic of adjustable capacitance value, and usually consist of a set of rotatable or movable plates. They are widely used in applications such as tuning circuits, radio frequency circuits and radios.

 

3.Film Capacitor: Plastic capacitors use plastic film as a dielectric, and metal electrodes are usually evaporated on the film. They have high temperature stability and durability and are suitable for high frequency and high temperature applications.Film Capacitors

 

4.Ceramic Capacitor: Ceramic capacitors use ceramic materials as dielectrics. They have advantages in small size, cheap price and high frequency application. Ceramic capacitors can be used in noise filtering, decoupling and timing circuits, etc.Ceramic Capacitors

 

5. Metal Film Capacitor: Metal film capacitors use metal film as the dielectric, usually by evaporating metal on plastic or metal foil. They have high precision and stability and can be used in precision circuits, audio applications and filter circuits, etc.

 

6.Multilayer Ceramic Capacitor, MLCC: Ceramic multilayer capacitor is a special kind of ceramic capacitor, which is composed of multiple thin ceramic sheets with metal electrodes in the middle. They are widely used in electronic equipment and feature high capacity, small size, and low cost.

 

7. Non-polar variable capacitor: The rotatable moving piece is a ceramic sheet coated with a metal film on the surface, and the fixed piece is a ceramic bottom coated with a metal film; the moving piece is a coaxial metal piece, and the fixed piece is an organic film as a medium. The advantage is that it is easy to produce and has low technical content. The disadvantage is that it is large in size and small in capacity. The non-polar variable capacitor can change the oscillation and resonant frequency circuit. FM, AM, transmit/receive circuits.

 

Ⅳ. The role of capacitance

 

1. Bypass

 

Bypass capacitors are energy storage devices that provide energy to local devices, which even out the regulator's output and reduce load demand. Like a small rechargeable battery, the bypass capacitor can be charged and discharged to the device. To minimize impedance, bypass capacitors should be placed as close as possible to the power and ground pins of the load device.Capacitor Kits

 

2. Sensors and Measurements

 

Certain capacitors are used as sensors and measurement devices, using changes in capacitance to detect changes in physical quantities or environmental conditions. For example, humidity sensors and touch screens use changes in capacitance to measure humidity and touch location.

 

3. DC blocker

 

Capacitors have a blocking effect on DC signals, allowing AC signals to pass while blocking DC signals. This is useful in some applications, such as coupling capacitors to block DC bias and pass only AC signals.Capacitor Hardware

 

4. Decoupling

Capacitors are often used for coupling and decoupling functions in circuits. Coupling capacitors can transfer signals from one circuit to another to achieve signal coupling and transmission. Decoupling capacitors are used to remove power supply noise and stabilize power supply voltage to maintain circuit stability and performance.

 

The decoupling capacitor acts as a "battery" to meet the change of the drive circuit current, avoid mutual coupling interference, and further reduce the high-frequency interference impedance between the power supply and the reference ground in the circuit.

 

5. Filtering

 

Capacitors are often used as part of filters in electronic circuits. They can attenuate or pass the signal of a specific frequency, so as to realize the function of filtering the signal in the circuit and removing noise. The capacitance value of the capacitor and other components in the circuit can determine the frequency response characteristics of the filter. It converts changes in voltage into changes in current. The higher the frequency, the greater the peak current, thereby buffering the voltage. Filtering is the process of charging and discharging.

 

6. Energy storage

 

The main function of a capacitor is to store charge. When a capacitor receives a voltage, the electric field causes a buildup of charge on the conductor, charging the capacitor. Such stored charge can be released when needed, providing temporary power or energy.

 

The storage capacitor collects charge through the rectifier and transfers the stored energy through the converter leads to the output of the power supply. Aluminum electrolytic capacitors with a voltage rating of 40-450VDC and a capacitance value between 220-150 000μF are more commonly used.

 

7. Energy storage and accumulators

 

Since capacitors can store electrical charge, they are widely used as energy storage. In a circuit, a capacitor stores electrical energy and releases it when needed to power other components or devices. This is useful in many applications such as energy storage systems, battery assist, backup power, etc.

 

8. Timers and oscillators

 

Capacitors can be combined with resistors and other components to form timer and oscillator circuits. By adjusting the values of capacitors and resistors, precise time delays and oscillation frequencies can be achieved for timing, timing control, and oscillation signal generation.

 

Ⅴ. Other capacitance-related parameters and properties

 

1. Polarity and non-polarity: Some capacitors, such as electrolytic capacitors, have polarity and need to be connected correctly. Whereas non-polarized capacitors, such as ceramic capacitors, do not have a specific polarity.

 

2.Voltage Rating: Capacitors have a maximum voltage that they can safely withstand. Exceeding the voltage rating may damage or rupture the capacitor.

 

3. Equivalent Series Resistance, ESR: The capacitor itself will have a certain equivalent series resistance, which will lead to energy loss and power consumption. The value of ESR depends on the type, size and quality of the capacitor.

 

4.Noise Characteristics: Capacitors may introduce noise or interfering signals, especially in high frequency applications. Therefore, for noise-sensitive applications, it is very important to choose low-noise capacitors.

 

5. Dissipation Factor: The detuning factor indicates the degree of energy loss of the capacitor at the operating frequency. A lower detuning factor means that the capacitor has lower energy loss at the operating frequency.

6.Frequency Range: Capacitors have an applicable operating frequency range. When this range is exceeded, the performance of the capacitor may be affected.

 

7.Temperature Coefficient: The capacitance value of a capacitor may change with temperature. The temperature coefficient expresses the percentage or fractional change in capacitance value with temperature.

 

Ⅵ. Application field of capacitor

 

1. Wireless communication and radio frequency applications: Capacitors are widely used in wireless communication and radio frequency circuits, including antenna tuners, filters, couplers and matching networks.

 

2. Electronic filters and audio applications: Capacitors play an important role in audio amplifiers, speakers and audio filters for sound processing, regulation and filtering.

 

3. Inductors and sensors: Some capacitors can be used as inductors and sensors, which use changes in capacitance value to detect changes in physical quantities or environmental conditions, such as humidity sensors and contact touch screens.

 

4. Timers and oscillators: By using RC circuits composed of capacitors and resistors, timer and oscillator circuits can be implemented for timing, frequency generation, and timing control.

 

5. Power filter: Capacitors are often used in power filter circuits to remove high-frequency noise and fluctuations in the power supply and provide a stable DC power supply.

 

6. Energy storage and battery auxiliary: Capacitors can be used as energy storage to store electrical energy and release energy when needed, such as flashlights, photographic equipment, and power tools.

 

7. Filters: Capacitors can be used to build filter circuits, including low-pass filters, high-pass filters, and band-pass filters, for signal processing and frequency selection.

 

Frequently Asked Questions

 

1. What are the common capacitance units?

 

The unit of capacitance is Farad, abbreviated as F.

 

But in practical applications, Farad is usually too large as a unit of capacitance. There is also Microfarad, which is abbreviated as μF, and 1 μF = 0.000001 F. Microfarad is a common capacitor capacity unit, especially suitable for medium capacity capacitors.

 

Picofarad, abbreviated as pF, 1 pF = 0.000000000001 F. Picofarads are capacitors used in very small capacities, such as those found in high-frequency circuits and microelectronics.

 

Nanofarad, abbreviated as nF, 1 nF = 0.000000001 F. Nanofarads are often used in smaller capacity capacitors, such as those found in integrated circuits.

 

2. What is the energy storage capacity of a capacitor?

 

The energy storage capacity of a capacitor refers to the electrical energy that a capacitor can store. During the charging process, the capacitor stores electrical energy in the electric field through the formation of the electric field and the accumulation of charges. The energy storage capacity of a capacitor depends on its capacitance value and the applied voltage. The energy storage capacity is directly proportional to the capacitance value, that is, the larger the capacity, the greater the energy that can be stored. At the same time, the amount of energy storage is also proportional to the square of the voltage, that is, the higher the voltage, the greater the energy that can be stored.