Capacitors are simple passive devices that can store electrical charges on their plates when connected to a voltage source.
The capacitor, like a small rechargeable battery, is a component capable or "capable" of storing energy in the form of an electric charge that produces a potential difference between its plates ( Static Voltage).
There are many different types of capacitors, from very small capacitor beads used in resonance circuits to large power factor correction capacitors, but they all do the same thing, storing loads.
In its basic form, a capacitor is used ceramic, plastic or some kind of liquid gel that is not interconnected or touching each other, but is used in air or waxed paper, mica, electrolytic capacitors.The insulation layer between a capacitor plates is commonly called Dielectric.
Due to this layer of insulation, the DC current cannot flow through the capacitor, since it blocks it, instead allowing the presence of a voltage in the form of an electric charge between the plates.
Conductive metal plates of a capacitor can be square, circular or rectangular, or cylindrical or spherical with the overall shape, size and structure of a capacitor with parallel plates depending on the application and voltage rating.
When used in a direct current or DC circuit, a capacitor charges up to the supply voltage, but prevents the current passing through it, as a capacitor does not have a dielectric conductor and is basically an insulator.However, when a capacitor is connected to an alternating current or AC circuit, the flow of the current appears to pass directly through the capacitor with little or no resistance.
There are two types of electrical charges: positive load in proton form and negative charge in electron form.When a DC voltage is placed in a capacitor, the positive (+and) load accumulates rapidly on one plate, the corresponding and opposite negative (-and) load accumulates on the other plate.For +and each charged particle that comes to a plate, a load with the same marking will be separated from the -and plate.
Then the plates remain unburied, and due to this load, a potential difference occurs between the two plates.When the capacitor reaches a stable state, an electric current cannot flow through the capacitor and around the circuit due to the insulation properties of dielectricin, which is used to separate the plates.
The flow of electrons on the plates is known as capacitor Charging Current, which continues to flow until the voltage on both plates (and therefore the capacitor) is equal to the applied voltage Vc.At this point, the capacitor is said to be "fully charged" with electrons.
The power or speed of this charging current is at its maximum value when the plates are completely empty (initial state), and while the plates charge between the capacitor plates to a potential difference equal to the source voltage, its value slowly drops to zero.
The amount of potential difference available throughout the capacitor depends on how much load is left on the plates by the work done by the welding voltage, as well as how much capacitance the capacitor has, and this is shown below.
The capacitor with parallel plates is the simplest form of the capacitor.Capacitance value in persian can be fixed with the surface area of the conductive plates and the distance between them and can be made using two metal or metalized foil plates at parallel distance to each other.Changing any of these values changes the value of the capacitance, which forms the basis for the operation of variable capacitors.
In addition, since capacitors store the energy of electrons in the form of an electric charge on the plates, the larger the plates and/or the smaller the separation between them, the greater the load the capacitor carries for any voltage given along the plates.In other words, larger plates, smaller distance, more capacitance.
By applying voltage to a capacitor and measuring the load on the plates, the ratio of Q load to V voltage will give the capacitance value of the capacitor, and therefore it is given as follows: C = Q/V this equation can also be re-ret. -arranged to give the known formula for the amount of load on the plates: Q = C x V
Although we have said that the load is stored on the plates of a capacitor, it is more accurate to say that the energy inside the load is stored in an "electrostatic field" between the two plates.When an electric current flows into the capacitor, it charges, making the electrostatic field much stronger as it stores more energy between the plates.
Likewise, as the current flowing from the capacitor drains it, the potential difference between the two plates decreases, and the electrostatic field decreases as the energy comes out of the plates.
The ability to store load in the form of electrostatic field on the plates of a capacitor is called capacitance of the capacitor.Not only that, but capacitance is characteristic of a capacitor that resists the voltage change on it.
Capacity of a Capacitor
Capacitance is the electrical property of a capacitor and is a measure of the ability of a capacitor to store an electrical charge on its two plates with its capacitance unit , which is the Farad (abbreviation F), named after the British physicist Michael Faraday.
Capacitance is defined as a capacitor having a Farad capacitance when a Coulomb charge is stored on plates with a voltage of one volt.Note that capacitance is always positive in value and is not a negative unit.However, farad is a very large unit of measurement to be used on its own, so the lower layers of the Farad are often used, for example, micro-farads, nano-farads and pica farads.
Standard Capacity Units
- Micropharmaceutical (μF) 1μF = 1/1,000,000 = 0.00001 = 10 -6 F
- Nanofarad (nF) 1nF = 1/1,000,000,000 = 0.000000001 = 10 -9 F
- picofarad (pf) 1pf = 1/1,000,000,000,000 = 0.00000000001 = 10 -12 F
Then, using the above information, we can create a simple table that will help us convert between pico-Farad (pF), nano-Farad (nF), micro-Farad (μF) and Farads (F), as shown.
|Pica-Farad (pF)||Nano-Farad (nF)||Micro-Farad (μF)||Farads (F)|
Capacity of Parallel Plate Capacitor
A parallel plate is proportional to the capacitance area of the capacitor, one meter 2 is the smallest of the two layers and the distance or separation, inversely proportional d given the meter between the two conductive plates (i.e. dielectric thickness).
The generalized equation for capacitance of a capacitor with parallel plates is given as follows: C = ε (A/d) ε here represents the absolute permeability of the dielectric material used.The dielectric constant, also known as the "permeability of that free space" ε, has a constant value of 8.84 x 10 -12 Farad/meter.
To make mathematics a little easier, this empty space dielectric constant, which can be written as 1/(4π x 9×10 9), ε it can also have constant picafarad (pF) units per meter. Issuer: 8.84 for free space value.Note that the resulting capacitance value will be in picafarad, not farad.
In general, the conductive plates of a capacitor are separated by a type of insulating material or gel instead of an excellent vacuum.When calculating the capacitance of a capacitor, we can consider the permeability of air, and especially dry air, as the same value as vacuum, since they are very close.
Capacitance Sample No1
A capacitor is made of two conductive metal plates of 30cm x 50cm with a 6mm range from each other and uses dry air as the only dielectric material.Calculate the capacitance of the capacitor.
The value of the capacitor, which consists of two plates separated by air, is then calculated as 221pF or 0.221nF.
Dielectric of a Capacitor
In addition to the total size of the conductive plates and their distance or range from each other, another factor affecting the overall capacitance of the device is the type of dielectric material used.In other words, the "permeability" of dielectricin (ε).
Conductive plates of a capacitor are usually made of a metal foil or a metal film that allows the flow of electrons and load, but the dielectric material used is always an insulator.Various insulation materials used as dielectrics in a capacitor differ in their ability to block or transmit an electrical charge.
This dielectric material can be made from a number of insulation materials or combinations of these materials, which are the most widely used types: air, paper, polyester, polypropylene, Mylar, ceramic, glass, oil or various other materials.
The factor of increasing the capacitor's capacitance compared to the air of dielectric material or insulator is known as dielectric constant , a dielectric material with a k and high dielectric constant is a better insulator than a dielectric material with a lower dielectric constant. .A dielectric constant is a sizeless quantity because it is relative to free space.
The actual permeability or "complex permeability" of the dielectric material between the plates is, in this case, the product of the permeability (ε o) and relative permeability (ε r) of the material used as dielectric and is given as follows:
In other words, if we take the permeability of free space as our base level ε and make it equal to one, when the vacuum of empty space is replaced with another type of insulating material, their dielectric permeability is referenced. "relative permeability" is the basic dielectric value of empty space, which gives a multiplication factor known as ε r.Therefore, the value of complex permeability will always be equal to one, ε the times of relative permeability.
Typical dielectric permeability, ε or dielectric constant units for common materials are: Pure Vacuum = 1.0000, Air = 1.0006, Paper = 2.5 to 3.5, Glass = 3 to 10, Mika = 5 to 7, Wood = 3 to 8 and Metal Oxide Powders = 6 to 20 etc. This gives us one last equation for the capacitance of a capacitor:
A method used to increase the overall capacitance of a capacitor while keeping its size small is to "intervene" more plates within a single capacitor body.Instead of just a number of parallel plates, a capacitor can have many separate plates connected to each other, so that the surface area of the plates increases A.
For a standard parallel plate capacitor, as shown above, the capacitor has two plates labeled A and B.Therefore, since the number of capacitor plates is two, we can say that it is n = 2 , where "n" represents the number of plates.
Then, for a single parallel plate capacitor, our equation above should really be as follows:
However, the capacitor can have two parallel plates, but only one side of each plate is in contact with the dielectric in the middle, since the other side of each plate forms the outside of the capacitor.If we take the two halves of the plates and combine them, we will have only "one" whole plate that is in contact with dielectric.
As for a single parallel plate capacitor, N – 1 = 2 – 1 equals 1 C (= ε o * ε r x 1 x A) / day is exactly the same: C = (ε o * ε R * A)/d is the standard equation above.
Now, let's say that we have a capacitor consisting of 9 intermittent plates, then let it be n = 9 as shown .
Now we have five plates connected to one cable (A) and four plates to the other cable (B).Then both sides of the four plates connected to end B are in contact with dielectric, while only one side of the outer plates connected to A is in contact with dielectric.Then, as above, the useful surface area of each group of plates is only eight, and therefore its capacitance is given as follows:
Modern capacitors can be classified according to the characteristics and characteristics of insulating dielectrics:
- Low Loss, High Stability such as Mika, Low K Ceramic, Polystyren.
- Medium Stability such as Medium Loss, Paper, Plastic Film, High K Ceramic .
- Polarized Capacitors such as Electrolytics, Tantalum .
Voltage Rating of a Capacitor
All capacitors have a maximum voltage rating and when choosing a capacitor, attention should be paid to the amount of voltage to be applied to the capacitor.The maximum voltage that can be applied to the capacitor without damaging the dielectric material is generally given in the information flutes as: WV , (operating voltage) or WV DC , (DC operating voltage).
If the voltage applied to the capacitor is too large, dielectric is broken (known as an electrical failure) and the arc occurs between the capacitor plates, resulting in a short circuit.The operating voltage of the capacitor depends on the type and thickness of the dielectric material used.
The DC operating voltage of a capacitor cannot be safely subjected to an alternative voltage of 100 volts, not the maximum DC voltage and maximum AC voltage as a capacitor with a voltage rating of 100 volts DC DC.An alternative voltage with an RMS of 100 volts will have a peak value of over 141 volts!( √ 2 x 100 ).
Then the operating voltage of a capacitor, which must operate at 100 volt AC, should be at least 200 volts.In practice, a capacitor should be selected so that the DC or AC operating voltage must be at least 50 percent larger than the maximum active voltage to be applied to it.
Another factor that affects the operation of a capacitor is Dielectric Leakage.Dielectric leakage occurs in a capacitor as a result of an undesirable leakage current flowing through dielectric material.
In general, it is assumed that the dielectric resistance is extremely high and that the DC current passing through the capacitor (as in an excellent capacitor) is a good insulator that prevents its flow from one plate to another.
However, if the dielectric material is damaged by excessive voltage or excessive temperature, the leakage current passing through dielectric will be extremely high, resulting in a rapid loss of load on the plates and overheating of the capacitor, resulting in premature failure of the capacitor.In this case, never use a capacitor in a circuit with a voltage higher than the nominal value of the capacitor, otherwise it may heat up and explode.
Introduction to Capacitor Summary
In this lesson, we found that the job of a capacitor is to store the electrical charge on its plates.The amount of electrical charge that a capacitor can store on its plates is known as the Capacity value and depends on three main factors.
- Surface Area – the surface area of the two conductive plates that make up the capacitor, A , the larger the area, the larger the capacitance.
- Distance – the distance between the two plates, d , the smaller the distance, the larger the capacitance.
- Dielectric Material – the type of material that separates the two plates called "dielectric", the higher the dielectric permeability, the greater the capacitance.
We also found that a capacitor consists of metal plates that do not touch each other, but are separated by a material called dielectric.The insulator of a capacitor can be air or even a vacuum, but it is usually a non-conductive insulating material such as waxed paper, glass, mica different types of plastic, etc. Dielectric provides the following advantages:
- Dielectric constant is the property of dielectric material and varies from one material to another, which increases capacitance by the k factor.
- Dielectric provides mechanical support between the two plates, ensuring that the plates are closer without touching each other.
- Dielectric permeability increases capacitance.
- Dielectric increases the maximum operating voltage compared to air.
Capacitors can be used in many different applications and circuits, such as blocking dc current when passing sound signals, pulses or alternating current or other time-changing waveforms.The ability to block DC currents allows capacitors to be used to soften the output voltages of power supplies, eliminating unwanted spikes in signals that could otherwise cause damage or incorrect triggering of semiconductors or digital components.
Capacitors can also be used to adjust the frequency response of an audio circuit or to combine separate amplifier stages that must be protected from the transmission of DC current.
In DC, a capacitor has infinite impedance (open circuit), the impedance of a capacitor at very high frequencies is zero (short circuit).All capacitors have a maximum operating voltage, WV DC, so choose a capacitor that is at least 50% higher than the supply voltage.
There is a wide range of capacitor styles and types, and each has its own advantages, disadvantages and characteristics.Including all types will make this training section very large, so in the next tutorial on Introduction to Capacitors we will limit them to the most commonly used types.