Capacitors: Structure, Types and Areas of Use

Capacitors, which are the circuit elements that serve to store electrical loads for a short time, are one of the most widely used materials in electronic designs. In this article, I will talk about the structure, types and areas of use of capacitors. Capacitors are produced by placing an insulator material between two conductive plates, and as a result of the electric field generated when voltage is applied to these two conductive plates, the capacitor stores the electric charge. The width of the conductive plates affects the capacity of the capacitor, while the type and thickness of the insulating material affect the operating voltage. Capacitors can be connected in series or parallel in electrical circuits. The unit of measurement is Farad. Capacitors have a fairly wide range of uses and types. In order for the design to be long-lasting, stable and function correctly, a capacitor suitable for the application should be selected. The following parameters can be taken into account when choosing a capacitor.

Whether it is Polar or Non-Polar:

While non-polar capacitors can be connected to the circuit in both directions, polar capacitors can be connected only in one direction. If the polar capacitors are connected inversely, they explode and cause damage to the environment and people.

Field of Application:

Capacitors are manufactured with different materials and in different physical structures, according to the application in hand. The main application areas are as follows.

Decoupling Capacitor, Bypass Capacitor:

They are the capacitors with the most common use. In electronic circuits, when different materials or circuits are connected to each other, oscillations in the supply voltage may occur. Decoupling capacitors create a stable voltage by eliminating these interferences. In particular, since the integrators are highly affected by interference, a capacitor should be placed close to the supply pins.

Coupling Capacitor:

They do not pass current when DC voltage is applied, and they become conductive when AC voltage is applied. As the frequency of the applied AC voltage increases, the series resistance of the capacitor decreases. By using this feature of capacitors, AC and DC signals can be separated from each other. We can show audio amplifiers as an example application. The serial capacitor connected to the signal input of these circuits shows high resistance at low frequencies, which does not block DC signals at all, so that both the audio input is protected from sudden DC signals and low-frequency noise in the sound is removed.

Low pass and high pass filter capacitor:

Capacitors can be used to filter high and low frequency.

“Capacitors have a fairly wide range of uses and types. In order for the design to be long-lasting, stable and function correctly, a capacitor suitable for the application should be selected. ”

Snubber Capacitor:

In applications where inductive loads are used, there may be instantaneous high voltage spikes due to the opposite EMC generated during switching. These spikes can cause the switching elements to malfunction, spreading the magnetic noise to the environment. Snubber capacitors are used to dampen these jumps. Usually, a low-resistance resistor connected to this capacitor consumes excess energy on itself. Specially manufactured snubber type capacitors are available for high power applications.

EMI/RFI Suppression Capacitors:

EMI (electro magnetic interference) is used to dampen RFI (radio frequency interference) signals. RFI is a high frequency EMI signal. It is usually used in devices connected to an AC mains line.
There are two different groups of standards as X and Y. Type X capacitors are connected between the phase and the neutral, dampening the interference from/to the mains. Y-type capacitors are connected between the phase or neutral and the earth or ground. They are used to dampen the interference between the device’s case and the mains, or to prevent the spread of interference in SMPS circuits. Capacitors of type X are divided into classes as X1, X2, X3, and the difference between them is the breakdown voltages. If these voltages are exceeded, the capacitor may be short-circuited. Fuse should be used in these circuits to prevent the risk of fire. The safety requirements are higher in Y-type capacitors. In case of a short circuit, this type of capacitor becomes an open circuit when high voltage is applied, as they can supply electricity to the device’s case. These capacitors are referred to as “safety type” capacitors. According to their breakdown voltages, they are classified as Y1, Y2, Y3, Y4. X type capacitor is produced with polyester, polypropylene, ceramic and metalized paper materials. Y-type capacitors, on the other hand, are usually produced in a ceramic disc structure.

Puls Capacitor:

It is usually used in high voltage and frequency applications where the capacitor is connected in series to the circuit. Fluorescent driver circuits can be given as an example application.

Trimmer Capacitor:

They are capacitors whose capacity can be changed by turning the screw in the case. Recently, their use has decreased.

Engine Starter Capacitor:

In order for induction-type single-phase motors to start rotating, it is necessary to create a phase difference. The capacitor connected in series to the auxiliary winding allows the motor to rotate by creating a phase difference.

Timer:

Capacitors can also be used for timing. These circuits are known as RCs. Depending on the value of the resistance connected to the capacitor in series, it will take a certain time for the capacitor to charge. With the help of transistor or opamp, this charging time can be used as a timer.

Super Capacitors:

It is a type of capacitor with a very high capacity, and usually preferred instead of batteries in RTC (real time clock) applications. It can maintain the stored electrical energy for a long time.

Types of Capacitors:

In order to meet different requirements, capacitors are manufactured by using different insulating materials and in different physical forms. The main types of capacitors are as follows.

Ceramic Capacitor:

Since the insulation coefficient of ceramic is very high, it offers the possibility of high voltage and capacity in smaller sizes. It is also non-polar. As a physical structure, it is divided into two groups as MLCC (multi layer ceramic capacitor) and ceramic disc. MLCC capacitors are manufactured by placing multiple layers on top of each other. They are the most widely used type of capacitor and can be manufactured in very small sizes. A ceramic disc is obtained by placing a ceramic material between two conductive discs. Ceramic capacitors are divided into three different classes according to the operating temperature range, operating tolerance and operating stability.

Class 1: It has high accuracy and low loss rate. The capacity change with temperature is low. It is especially preferred in resonance circuits. It has codes such as NP0, N33, N75.
Class 2: It has high value capacity, and the tolerance range is less than ±15%. The operating temperature range can exceed -55°C to +125°C. Coupling is preferred for decoupling applications. There are codes such as X7R, X5R.
Class 3: It offers higher value capacity possibilities compared to Class 2, its tolerance is higher and its temperature range is lower.

The disadvantage of class 2 and class 3 ceramic capacitors compared to film capacitors is that their capacity changes more depending on the frequency and applied voltage. That is why they are not preferred in some applications.

Film Capacitor:

Film capacitors are non-polar capacitors manufactured by coating aluminum or zinc on plastic film. The plastic film, on which the metal coating is made, is rolled and connected to the metal plates from the two ends of the roll. In this way, multiple parallel capacitors are connected to each other. Due to the shortness of the conductive path, their internal resistance is quite low. Plastic film is manufactured from materials such as Polypropylene (PP), Polyester (PET), Polyphenylene sulfide (PPS), Polyethylene naphthalate (PEN) or Polytetrafluoroethylene. According to the intended use, each material offers different advantages. Structurally, it is divided into three groups.

“Every capacitor has an internal resistance and inductance. In particular, the capacitors used for verification purposes in SMPS and similar circuits should be of “low ESR” type. ”

a. Single-sided metalized film capacitor: The metal coating is made on only one surface of the plastic film. The current resistance is low.
b. Double-sided metalized film capacitor: The metal coating is made on both surfaces of the plastic film. The current resistance is higher. It is preferred in high frequency pulse applications.
c. Film/foil capacitor: It is made by adding metal foil between two plastic films instead of metal coating. The current resistance is much higher.

Power Film Capacitor:

Structurally, the film is quite similar to the capacitor. It is customized for high power applications, and resistant to high voltage and current.

Electrolytic Capacitor:

The surface of the metal serving as anode is oxidized and turned into an insulator. In this way, the place between the anode metal and the cathode is coated with an insulating material. The surface of the anode metal is roughened and the contact surface is expanded, to make it possible to reach higher capacities. In the cathode part, on the other hand, two different groups of materials are used as “solid” and “liquid”. It is a kind of polar capacitor and may explode if it is connected in reverse. With its ability to reach high capacity values, it is used in several different applications. It is divided into three groups depending on the anode material used.

a. Aluminum electrolytic capacitors: Aluminum foil is used as the anode metal. The surface is coated with aluminum oxide, which is an insulator. Conductive liquid or conductive solid materials are used on the cathode side. This material is selected based on different needs, and conductive liquid is used intensively as its cost is low. Conductive polymer is used in Low ESR models.
b. Tantalum electrolytic capacitors: Tantalum material is used as anode metal, and its surface is coated with tantalum pentoxide, which is also an insulator. On the cathode side, conductive liquid or solid materials are used. Conductive polymer is used in Low ESR models. It has three times more capacity than aluminum. It is more preferred in small areas.
c. Niobium electrolytic capacitors: It is a product whose use is quite decreased recently.

ESR (Equivalent Series Resistance) and ESL (Equivalent Series Inductance):

These are the parameters that should be taken into account for capacitors. Every capacitor has an internal resistance and inductance. In particular, the capacitors used for verification purposes in SMPS and similar circuits should be of “low ESR” type. During rectification, ripple voltages are damped by the capacitor, causing ripple currents to pass through it. If the ESR resistance is high, this causes the capacitor to heat up.

Operating Temperature:

Particular attention should be paid to the operating temperature when choosing a capacitor. The response of each type of capacitor to temperature is at different levels. Capacitors may lose their capacity values when exposed to heat for a long time.

Operating Current:

Capacitors are generally not suitable for high and continuous current flow. However, if they should be used in this way, a type of capacitor suitable for this purpose should be selected and the current values given in the relevant datasheet should be followed. If more current passes through than it should and too much voltage is applied, the capacitor may short circuit or deform. This may cause security vulnerabilities to occur.