What is a capacitor? Structure, operating principle and function of capacitors

17-11-2024
5:00 pm

If you are new to refrigeration, you may be wondering What is a capacitor?, what is its use and how does it work. To help readers better understand capacitor, Tan Long Please refer to the detailed article on this topic below.

What is a capacitor? Structure, operating principle and function of capacitors

Content

What is a capacitor capacitor?

Capacitor is an electronic device used to store electric charge and energy. It is widely used in electronic circuits for noise filtering, voltage balancing, oscillation, and many other applications. Capacitor can be classified according to electrode type, dielectric type, capacity, voltage, frequency, size and shape.

The shape of a capacitor in practice

This is what the capacitor actually looks like.

What is the structure of a capacitor?

Beyond Concept What is a capacitor? Many people want to learn about its structure. Capacitor consists of at least two electrical conductors, usually in the form of metal plates, placed parallel and separated by a dielectric layer.

Capacitor lead can be foil or film. Dielectric are non-conductive materials such as glass, chemically impregnated paper, ceramic, mica, plastic film or air. Dielectric This helps increase the capacitor's ability to store electrical energy. Depending on the type dielectric, capacitors have corresponding names.

Describe the detailed structure of a capacitor.

Capacitance, units and symbols of capacitors

Capacitance is a quantity that represents the ability of a capacitor to store electricity. Capacitance depends on the area of the electrode, the material of the dielectric and the distance between the two electrodes, calculated by the formula:

C = ξ . S / d

In there:

C: Capacitance of the capacitor

ξ: Dielectric constant of the insulating layer

S: Capacitor plate area

d: Insulation thickness

Unit of capacitance of capacitor: The unit of capacitance is the Farad (F), but because 1 Farad is so large, smaller units are often used such as:

MicroFara (µF): 1 Farad = 1,000,000 µF
NanoFara (nF): 1 Farad = 1,000,000,000 nF
PicoFara (pF): 1 Fara = 1,000,000,000,000 pF
1 µF = 1.000 nF
1 nF = 1.000 pF

Capacitor symbol: Capacitor is denoted by C (Capacitor).

Dielectric: Dielectric is a poor conductor of electricity, with high resistivity (10⁷ ÷ 10¹⁷ Ω.m) at normal temperature. Insulators include mostly inorganic and organic materials.

Common capacitor classification

Common types of capacitors

Electrolytic Capacitor (Polarized Capacitor)

Electrolytic capacitors are a type of capacitor polarized, meaning that when used, you need to connect the correct pins of the capacitor to the supply voltage. The pins of electrolytic capacitors are usually marked with a (+) or (-) symbol.

Electrolytic capacitors are polarized capacitors.

There are two types of capacitors:

Electrolytic capacitor with legs at both ends of a cylindrical shape
Electrolytic capacitor has two legs connected to the same cylindrical end.

The maximum voltage that the capacitor can withstand is usually written on the body of the electrolytic capacitor. If the voltage exceeds this limit, the capacitor may swell or explode, causing danger. The value of the electrolytic capacitor is written on the body, for example 10µF, 100µF.

Non-polar capacitor

Non-polar capacitor no specified positive or negative polarity, usually flat and small capacitance from 0.47µF or less. This type of capacitor can be replaced by a polarized capacitor and is easily installed without regard to polarity.

Non-polar capacitor used in high frequency circuits, as noise filtering circuits and in household appliances such as pumps, motors, and grid phase compensation capacitors.

Supercapacitor

Supercapacitor has very high energy density (supercapacitor), such as Li-ion capacitors (LIC capacitor). These capacitors can store electricity for several months, providing power instead of batteries to store data in electronic devices. They have the ability to discharge quickly and contain a lot of energy, and are used in transportation to harvest braking energy, providing sudden peak power for electric cars, trams, and high-speed trains.

What is the use of each type of capacitor?

Polarized capacitor (electrolytic capacitor)

Polarized capacitor or electrolytic capacitor Often used in low frequency circuits such as power filter circuits. This capacitor contains large capacitance without taking up much space. However, it is necessary to connect the correct polarity, otherwise the capacitor will be damaged. The life of electrolytic capacitors is shorter than other types of capacitors.

Polarized capacitors or electrolytic capacitors are often used in low frequency circuits.

Non-polar capacitor

Capacitor Non-polar capacitors are used in high frequency circuits and noise filtering circuits. They do not require correct polarity and usually have small capacitance. Non-polar capacitors are commonly used in household electrical appliances such as fans and motors.

Variable capacitor

Variable capacitor can change the capacitance value and is often used in circuits that require adjustable capacitance such as frequency regulators. Variable capacitor values are typically between 100pF and 500pF.

Supercapacitor

Supercapacitor Supercapacitors have very high capacitance density and are used in devices that require large amounts of instantaneous power, such as elevators, cranes, cars, and mobile devices. Supercapacitors store a lot of energy, charge and discharge quickly, and have a longer lifespan than conventional batteries. They are advanced energy storage technology.

Standard formula for calculating capacitor capacitance

Capacitors in series

When capacitors are connected in series, the equivalent capacitance $C_{td}$ is calculated by the formula:

$1Ctd=1C1+1C2+1C3frac{1}{C_{td}} = frac{1}{C_1} + frac{1}{C_2} + frac{1}{C_3}$

In case of 2 capacitors connected in series:

$Ctd=C1⋅C2C1+C2C_{td} = frac{C_1 cdot C_2}{C_1 + C_2}$

Equivalent capacitor withstand voltage:
The total voltage is equal to the sum of the voltages of each capacitor:

$U_{td} = U_1 + U_2 + U_3$

Note: When connecting electrolytic capacitors in series, make sure the negative terminal of the previous capacitor is connected to the positive terminal of the next capacitor.

Capacitors in parallel

When capacitors are connected in parallel, the equivalent capacitance $C_{td}$ is calculated by the sum of the capacitance of the capacitors:

$C_{td} = C_1 + C_2 + C_3$

Withstand voltage:
The equivalent voltage is equal to the lowest voltage among the capacitors.

Note: If it is an electrolytic capacitor, the capacitors need to be connected in the same positive and negative direction to avoid damage.

Compare:

Capacitors in series	Capacitors in parallel
Equivalent capacitance reduction	Equivalent capacitance increases
Total voltage increase	Equivalent voltage remains the same

Standard formula for calculating capacitor capacitance

How to read capacitance value on capacitor

With capacitor

The capacitance value of the electrolytic capacitor is written directly on the capacitor body.

Note: Electrolytic capacitors are polarized (with (-) and (+) signs) and are always cylindrical in shape.

For example, a electrolytic capacitor has a value of 185 µF / 320 V.

With paper capacitors and ceramic capacitors

Paper and ceramic capacitors have their capacitance values written in symbols, not direct numbers.

Reading: Take the first two digits and multiply by $10$ third power

For example: Ceramic capacitors are labeled with the value 474K, means: $10^4 = 470,000 , text{pF} = 470 , text{nF} = 0.47 , mu F$ Letter K at the end represents the capacitor error, usually 10%.

Attention:

K or J Capacitor error only (K = 10%, J = 5%).
50V is the maximum voltage that the capacitor can withstand.

Other ways of writing values

Paper and ceramic capacitors can also have their values stated using decimals and units of microfarads (µF).

Every capacitor has a maximum voltage value written after the capacitance value, this is the voltage level the capacitor can withstand. If the voltage exceeds this level, the capacitor may be damaged or explode.

Note when installing capacitors into the circuit:

When installing a capacitor in a circuit with voltage $U$ , usually choose a capacitor with a maximum voltage value about 1.4 times higher than the circuit voltage value.

For example:

12V circuit needs 16V capacitor.
24V circuit needs 35V capacitor.
…and so on.

What is the working principle of capacitor?

Capacitors have the ability to store energy in the form of an electric field by accumulating electrons. They can release these charges to create an electric current. This is the charge-discharge property of the capacitor, which allows the capacitor to conduct alternating current.

When the voltage between the two circuit boards changes slowly over time, the charging or discharging of the capacitor can cause explosions and sparks due to the sudden increase in current. This is the charging-discharging principle of the capacitor, a fairly common phenomenon.

Instructions to check if capacitor is still working or not?

To check capacitor still working well or not, you can use multimeter or LCR clip. Before testing, make sure the capacitor is completely discharged to avoid the risk of electric shock or damage.

Test paper capacitors and ceramic capacitors

Paper and ceramic capacitors often fail in the form of leakage or short circuit. To detect these failures, we can perform the following test measurements:

Test instructions:

In the image below, we have three capacitors C1, C2 and C3 with equal capacitance, in which:
- C1 is a good capacitor
- C2 is a leak capacitor
- C3 is the capacitor shorted
Check capacitor C1 (good capacitor): The meter needle will shoot up a little and then return to its original position. (Note: for capacitors smaller than 1nF, the meter needle may not charge).
Check capacitor C2 (leaking capacitor): The clock hand will go up part of the scale and stop, not returning to its original position.
Check capacitor C3 (shorted capacitor): The meter needle will go up to 0 Ω and not return.

Note: When measuring paper or ceramic capacitors, set the meter to the x1KΩ or x10KΩ scale, and turn the meter clockwise several times for accurate testing.

Check capacitor

Electrolytic capacitors are less likely to leak or short out than paper capacitors, but they often fail due to drying of the chemicals inside the dielectric, resulting in a loss of capacitance. To test an electrolytic capacitor, we need to compare the discharge of the capacitor with a good capacitor of the same capacitance.

Test instructions:

Suppose we have a capacitor C2 with a value of 100µF and want to check if it has lost its capacitance. We will compare it with a new capacitor C1 with the same value of 100µF.
Set the multimeter to the x1Ω to x100Ω scale (lower scale for large capacitors).
Measure and compare the discharge of both capacitors, and reverse the measuring probe to get accurate results.

Evaluation of results:

If both capacitors discharge the same, capacitor C2 is still good.
If capacitor C2 discharges less well, it means that capacitor C2 is dry, reducing capacitance.
If the meter needle does not return after measuring, it is a sign of a leaking capacitor.

Uses of capacitors

The most notable use of capacitors is their ability to store electrical energy and charge efficiently, similar to batteries. However, the strength of capacitors is their ability to store energy without dissipating it, which makes them a superior choice in many applications.

In addition, the capacitor allows alternating current (AC) voltage to pass through, turning the capacitor into a conductive component like a general-purpose resistor. In particular, as the frequency of the AC current increases and the capacitance of the capacitor becomes larger, its capacitive reactance will decrease, supporting the process of circulating voltage through the capacitor effectively.

Capacitors work on a smart charge-discharge principle, blocking direct current (DC) voltage while allowing alternating current (AC) to flow. This allows the capacitor to transfer signals between amplifier stages with voltage differences.

In addition, capacitors also play an important role in filtering AC voltage into stable DC voltage, by eliminating the negative phase.

Applications of capacitors in practice

Capacitors are widely used in the fields of electrical and electronic engineering:

Car audio system: Capacitors help store energy for the amplifier, ensuring a steady supply of power when needed.
Computers and digital memory: Capacitors are used in dynamic memories of binary computers, especially in devices using electron tubes.
Military and special manufacturing: Capacitors play an important role in power generation systems, physics experiments, radar, nuclear weapons, and many other applications in the defense industry.
Energy supply and energy storage: The most common application of capacitors is in the supply and storage of electrical energy.

In addition to the above main applications, capacitors are also used in many other fields such as signal processing, motor starting, control circuits, and many other electronic applications.

Capacitors have the ability to store electrical energy efficiently.

Here is some information about capacitors, including definitions. What is a capacitor?, structure, function and operating principle of it. Hope the article is useful for you, visit Tan Long to refer to more useful information!