What is a Capacitor? Capacitor Types, Capacitor Uses, and Capacitor Working– A Capacitor is one of the most basic electronic components that is used in almost all kinds of electronic circuits for storing, surge suppression and filtering. It is a widely used and important component in the family of electronics. I have been using capacitors in almost all of my projects, pure electronics and controller based. Just like the resistors, capacitors are passive electronic components to store an electric charge. The amount of charge that it can store depends on the distance between the plates.
A capacitor (historically known as a “condenser”) is a device that stores energy in an electric field, by accumulating an internal imbalance of electric charge. It is made from two conductors separated by a dielectric (insulator). Using the same analogy of water flowing through a pipe, a capacitor can be thought of as a tank, in which the charge is often thought of as a volume of water within the tank. The tank can “charge” and “discharge” in the same manner as a capacitor does to an electric charge. A mechanical analogy is that of a spring. The spring holds a charge when it’s pulled back.
Capacitance of a Capacitor
The Capacitance of a Capacitor can be defined as the amount of charge that a capacitor can store per unit of voltage across its plates is its capacitance, designated C. That is, capacitance is a measure of a capacitor’s ability to store charge. The more charge per unit of voltage that a capacitor can store, the greater its capacitance, as expressed by the following formula:
Where C is capacitance Q is charge, and V is voltage.
By rearranging the terms in above equations, you can obtain two other formulas.
The Unit of Capacitance: The farad (F) is the basic unit of capacitance. Recall that the coulomb (C) is the unit of electrical charge.
One farad is the amount of capacitance when one coulomb (C) of charge is stored with one volt across the plates.
Most capacitors that are used in electronics work have capacitance values that are specified in microfarad µF and picofarad (pF). A microfarad is one millionth of a farad, (1 µF =10-6F) and a picofarad is one trillionth of a farad (1 pF = 10-12 F).
How a Capacitor Works
Electric current is the flow of electrical charge, which is what electrical components harness to illuminate, or spin, or do whatever they are doing. When current flows into a capacitor, the charges get “stuck” on the plates because they cannot get pass the insulating dielectric. Electrons — negatively charged particles — are sucked into one of the plates, and it becomes overall charged. The mass of negative charges on one plate pushes away like charges on the other plate, making it positively charged.
The positive and negative charges on each of those plates attract one another, because that is what opposite charges do. But, with the dielectric sitting between them, the maximum amount as they need to return together, the charges will forever be stuck on the plate (until they have elsewhere to go). The stationary charges on these plates create an electrical field, which influences potential energy and voltage. When charges group together on a capacitor like this, the cap is storing electric energy even as A battery might store energy.
The working voltage is most important of all the characteristics. There is a working voltage is written on the capacitors which refer to the maximum voltage that can be applied across the capacitor. It refers the DC voltage.
It is safe to operate the capacitor within its rated voltage. Otherwise, it may damage the capacitor. If the voltage applied is greater than the working voltage of the capacitor, the dielectric will breakdown. The working voltage depends on the dielectric material and the thickness of the dielectric. The working voltage depends on the dielectric material and the thickness of the dielectric. So always the working voltage of the capacitor is the maximum voltage of the capacitor that can be applied. In practice, a capacitor should be selected so that its working voltage is at least 50% greater than the highest effective voltage applied to it.
Fixed capacitor is a sort of capacitor which provides fixed amount of capacitance (capacitance means ability to store electric charge). In other words, fixed capacitor may be a sort of capacitor that stores fixed amount of electrical charge which isn’t adjustable.
Fixed capacitors are classified into differing types supported the dielectric material wont to construct them. the various types of fixed capacitors are:
You might be thinking why is it called a Paper Capacitor? You know? Paper capacitor is also known as a fixed capacitor, and it is called a Paper Capacitor, because in this type of the Capacitor paper is used as a dielectric medium, that stores energy in the form of the electrical field. These capacitors are used at power line frequency with a capacitance value of 1nF to 1uF. It stores a fixed amount of electric charge.
A paper capacitor or Fixed Capacitor is made up of two metallic plates with a dielectric material paper between them. It has positive and negative plates. When a small amount of electric charge is applied over the plates, the positive charge is attracted to one plate and a negative charge is attracted to another plate. This electrical energy is stored in the form of the electrical field. This stored electrical energy is used by the discharging of a capacitor. These are available in the range of 500pF to 50nF. These offer high leakage currents.
Among the other types of the capacitors, Mica capacitors are the most stable, reliable and high precision capacitors. These capacitors are available from low voltages to high voltages. Mica capacitors are used in the applications where high accuracy and low capacitance change over the time is desired. These capacitors can work efficiently at high frequencies.
Mica is a group of natural minerals. Silver mica capacitors are capacitors which use mica because the dielectric. There are two sorts of mica capacitors: clamped mica capacitors and silver mica capacitors. Clamped mica capacitors are now considered obsolete thanks to their inferior characteristics. Silver mica capacitors are used instead. they’re made by sandwiching mica sheets coated with metal on each side. This assembly is then encased in epoxy so as to guard it from the environment. Mica capacitors are mainly used when the design calls for stable, reliable capacitors of relatively small values. they’re low-loss capacitors, which permit them to be used at high frequencies, and their value doesn’t change much over time.
Ceramic capacitors are utilized in high frequency circuits like audio to RF. they’re also the simplest choice for high frequency compensation in audio circuits. The Ceramic capacitors are also known as disc capacitors. Ceramic capacitors are made by coating two sides of a little porcelain or ceramic disc with silver and are then stacked together to form a capacitor. One can make both low capacitance and high capacitance in ceramic capacitors by changing the thickness of the ceramic disc used. The ceramic capacitor is shown in figure below.
They exhibit large non-linear changes in capacitance against temperature and as a result are used as decoupling or bypass capacitors as they’re also non-polarized devices. Ceramic capacitors have values starting from a couple of picofarads to at least one or two microfarads, (μF) but their voltage ratings are generally quite low.
Ceramic sorts of capacitors generally have a 3-digit code printed onto their body to spot their capacitance value in pico-farads. Generally, the primary two digits indicate the capacitors value and therefore the third digit indicates the amount of zero’s to be added. for instance, a ceramic disc capacitor with the markings 103 would indicate 10 and three zeros’ in pico-farads which is like 10,000 pF or 10nF.
Film Capacitors are consisting of a relatively large family of capacitors with the difference being in their dielectric properties, are the most commonly available of all types of capacitors. These include polyester (Mylar), polystyrene, polypropylene, poly carbonate, metalized paper, Teflon etc. they’re available in almost any value and voltages as high as 1500 volts. they are available in any tolerance from 10% to 0.01%. Film capacitors additionally arrive during a combination of shapes and case styles. There are two sorts of film capacitors, radial lead type and axial lead type. The electrodes of film capacitors could also be metalized aluminum or zinc, applied on one or each side of the film, leading to metalized film capacitors called film capacitors.
Electrolytic Capacitors are almost used in all electronic circuits, they are most frequently used in power supplies as the decoupling capacitors, these are the most frequently used capacitors and have a good tolerance capacity. Just like resistors, capacitors are available in different sizes. The electrolytic capacitors are polarized. These capacitors have the positive and ground legs. The ground leg is provided with a long strip. Another identification can be, the positive leg is slightly longer than the ground leg. But in many situations, when both the legs are of the same size, then the long strip on one side of the capacitor is used as the identification, the leg on the strip side will be the ground leg. Electrolytic capacitors can be found with working voltages up to about 500V, although the very best capacitance values aren’t available at high voltage and better temperature units are available, but uncommon. There are two sorts of electrolytic, tantalum and aluminum in common.
Tantalums capacitors have ordinarily better exhibition, higher value, and are ready just during a more limited extend of parameters. The dielectric properties of tantalum oxide is far superior to those of alumina giving a neater leakage current and better capacitance strength which makes them suitable for obstructing, decoupling, filtering applications.
The thickness of the alumina film and heightened breakdown voltage gives the capacitors exceptionally elevated capacitance values for his or her size. during a capacitor the foil plates are anodized by a dc current thus setting of the extremity of plat material and confirming polarity of its side.
A Variable Capacitor is that type of a capacitor whose capacitance can be changed mechanically. These types of the capacitors are provided with knobs or screw. These type of capacitors are used in circuits where we need to adjust the frequency i.e. frequency of resonance in LC circuits, as an example, to regulate the radio for impedance matching in antenna tuner devices.
There are many uses of these variable Capacitors such as for tuning in LC circuits of radio receivers, for impedance matching in antennas etc. The main types of variable capacitors are Tuning capacitors and Trimmer capacitors.
Tuning capacitors are popular sort of variable capacitors. The tuning capacitors contain a stator, a rotor, and a frame to support the stator and a mica capacitor. The constructional details of a tuning capacitor are shown within the following figure.
The stator may be a stationary part and the rotor rotates by the movement of a movable shaft. The rotor plates when moved into the slots of stator, are available on the brink of form plates of a capacitor. When the rotor plates sit completely within the slots of the stator then the capacitance value is maximum and once they don’t, the capacitance value is minimum.
Trimmer capacitors are varied employing a screwdriver. Trimmer capacitors are usually fixed in such an area where there’s no got to change the worth of capacitance, once fixed.
There are three leads of a trimmer capacitor, one connected to the stationary plate, one to rotary and therefore the other one is common. The movable disc may be a semi-circular shaped one. A trimmer capacitor would appear as if those within the following figure.
There are two parallel conducting plates present with a dielectric within the middle. The constructional of a trimmer capacitor is as shown below.
One of the 2 plates is movable, while the opposite is fixed. The dielectric material is fixed. When the movable plate is moved, opposite to the world between the movable and glued electrode, then the capacitance is often changed. The capacitance is going to be higher if the other area gets bigger, as both the electrodes act as two plates of a capacitor.
Construction of a Capacitor
The device consists of two parallel conducting metal plates which are separated by an insulator called dielectric. The conducting material is made up of aluminum or other metal and the dielectric can be made up of ceramic, glass, paper or plastic. The metal plates of a capacitor can be either square, circular or rectangular, or they can be of any other shape and size. A two lead is brought out from each plate to enable the device to be connected to a circuit.
When a voltage is applied to the two leads through a battery source, the charge deposits on the plates of the capacitor. As long as this voltage is equal to battery voltage (E) the circuit is in balance condition. When we break the connection of the battery the charges cannot flow away and the voltage remains stable between the two plates. This combination of two plates, which are separated by an insulator and which are able to store some amount of electricity is called a capacitor or condenser.
Capacitors are used in almost all kinds of electronic circuits. The capacitors may be polarized or non-polarized, fixed or variable. Capacitors serve several essential applications in circuit design, providing flexible filter options, noise reduction, power storage, and sensing capabilities for designers.
Combined with resistors, capacitors are often used as the main element of frequency-selective filters. The available filter designs and topologies are numerous and can be tailored for frequency and performance by selecting the proper component values and quality. Some of the types of filter designs include:
- High Pass Filter
- Low Pass Filter
- Band Pass Filter
- Band Stop Filter
- Notch Filter
- All Pass Filter
- Equalization Filter
You might have seen capacitors soldered near the supply pins of the chips, or at the input and output pins of the voltage regulators, these are Decoupling capacitors. Capacitors play a critical role in the stable operation of digital electronics by protecting sensitive microchips from noise on the power signal, which can cause anomalous behaviors. Capacitors used in this application are called decoupling capacitors and should be placed as close as possible to each microchip to be most effective, as all circuit traces act as antennas and will pick up noise from the surrounding environment. Decoupling and by-pass capacitors are also used in any area of a circuit to reduce the overall impact of electrical noise.
Coupling or DC Blocking Capacitor
Capacitors are often used for separating the AC and DC components. Since capacitors have the ability to pass AC signals while blocking DC, they can be used to separate the AC and DC components of a signal. The value of the capacitor does not need to be precise or accurate for coupling, but it should be a high value, as the reactance of the capacitor drives the performance in coupling applications.
In circuits where a high-inductance load is driven, such as a motor or transformer, large transient power spikes can occur as the energy stored in the inductive load is suddenly discharged, damaging components and contacts. Applying a capacitor can limit, or snub, the voltage spike across the circuit, making the operation safer and the circuit more reliable. In lower-power circuits, using a snubbing technique prevents spikes from creating undesirable radio frequency interference that generates anomalous behavior in circuits and causes difficulty in gaining product certification and approval.
Pulse Power Capacitors
At their most basic, capacitors are effectively tiny batteries that offer unique energy storage capabilities beyond those of chemical-reaction batteries. When lots of power is required in a short period of time, large capacitors and banks of capacitors are a superior option for many applications. Capacitor banks are used to store energy for applications such as pulsed lasers, radars, particle accelerators, and railguns. A common application of the pulsed-power capacitor is in the flash on a disposable camera, which is charged then rapidly discharged through the flash, providing a large pulse of current.
Resonant or Tuned Circuit Applications
While resistors, capacitors, and inductors make filters, certain combinations can also result in resonance amplifying the input signal. These circuits are used to amplify signals at the resonant frequency, create high voltage from low voltage inputs, as oscillators and as tuned filters. In resonant circuits, care must be taken to select components that can survive the voltages that the components see across them or they will quickly fail.
Capacitive Sensing Application
Capacitive sensing has recently become a common feature in advanced consumer electronics devices, although capacitive sensors have been used for decades in a variety of applications for positions, humidity, fluid level, manufacturing quality control, and acceleration. Capacitive sensing works by detecting a change in the capacitance of the local environment through a change in the dielectric—a change in the distance between the plates of the capacitor, or a change in the area of a capacitor.
Photo Credit: Wikipedia