Capacitors Tutorial

  

 

At this page (1) Page 2
⚛ Definition of Capacitor - Capacity in Units ⚛ Reading Ceramic Capacitor Value Gates
⚛ Charging - Discharging a Capacitor ⚛ Electrolytic Capacitors
⚛ Capacitor Phisical Structure ⚛ Electrolytic Aluminum Capacitors
⚛ Capacitor behavior in continous AC current ⚛ Electrolytic Aluminum Capacitors Vertical - Horizontal
⚛ Characteristics of Capacitors ⚛ Code of Electrolytic Cylinder Capacitors
⚛ Types of Capacitors ⚛ Super Capacitors
⚛ Dielectric Characteristics ⚛ Variable Capacitors
⚛ Paper Capacitors ⚛ Adjustable Capacitors
⚛ Plastic Film Capacitors ⚛ Uses of Variable Capacitors
⚛ Mica Capacitors  
⚛ Glass Capacitors Page 3 (Capacitor Values and conversion Tables I)
⚛ Oil Capacitors  
⚛ Ceramic Capacitors Page 4 (Capacitor Values and conversion Tables II)

 

 

 

Definition of Capacitor - Capacity in Units

A capacitor is consisting of two conductive plates which are separated from each other by an insulating material. The conductive plates are called reinforcements and the insulating material is called dielectric. The capacitor has the ability to hold the electric load on its reinforcements when a tension is applied to its ends. The amount of charge the capacitor can hold depends on the surface area of its reinforcements and the distance between the reinforcements. The larger the reinforcement surface area and the smaller the spacing between the reinforcements, the greater the load can hold. The kind of dielectric material plays a very important role in holding the load expressed by the term capacitance. So the capacity of a capacitor to store energy is called capacity.

The capacity of a capacitor is denoted by the letter C and its unit of measurement is Farad. Because Farad (F) is a large capacity in the capacitors, Farad subdivisions are used as we see below:
1F = 1000mF, 1mF = 1000μF, 1μF = 1000nF, 1nF = 1000pF. To make it easy to understand the units, imagine a staircase, with the maximum capacity and the shorter one as shown: F> mF> μF> nF> pF. Each stair downwards is multiplied by 1000, while when climbing from the bottom up we divide by 1000. For example, a capacitor that is 470nF is equal to 0.47μF, or a capacitor that is 2.2nF is equal to 2200pF, and so on.

 

 

Charging / Discharging a Capacitor

The effect of absorbing electrical charge from a capacitor is called charging of the capacitor while the release of the charge is called discharge of the capacitor. In many cases, in a particular part of our electronic circuit, the flow of electricity does not have a fixed value, but it varies with time. This can be achieved by the series-capacitor-to-capacitor connection.

With the SW switch closed, the current flows through the resistor R and charges the capacitor. The rate at which the capacitor is charged depends on the values ​​of the resistor and the capacitor. With a relatively low value of the resistor the capacitor is charged quickly (almost instantly) and as the value of the resistor increases (either the capacitor or both), the charging takes longer.

We notice that during the charging of the capacitor the voltage at its ends increases until almost the voltage value of the source is reached, so the charging is practically stopped. At the same time the current flowing to the capacitor during charging decreases as the charged capacitor behaves like a resistor with very high resistance.

The capacitor will be discharged instantly by pressing the PS thrust switch. We may wish to give some time delay to the discharge of the capacitor. The discharge is gradually being made. This can be done exactly in the same way as in the case of charging. 

 

capacitor charge discharge

 

As in the case of charging, the rate at which the capacitor is discharged depends on the value of the resistor and the capacitor. The capacitor discharges quickly and as the value of either the resistor (or the capacitor or both) increases, the discharge takes longer. We notice that during discharge of the capacitor the voltage at its ends decreases until it reaches almost 0V, when the discharge is practically stopped. The capacitor at this point behaves like a resistor with too little resistance, ready for a new charging-discharge cycle.

 

 

Capacitor Phisical Structure

As mentioned above, the materials for the construction of a capacitor, as well as the way it is constructed, determine its capacitance. Usually, as a reinforcement of a capacitor, brass, galvanized iron or aluminum metals are used. For the construction of dielectric in a capacitor, non-conductive materials such as paper, oil, glass, air, tantalum, polypropylene, mica and many other materials are used. The element used by the capacitor as a dielectric, classifies it as a variety of names (polypropylene capacitors, tantalum capacitors, etc.), which have some special characteristics and are therefore used in specially designed circuits.

Ceramic capacitor structure

Electrolitic capacitor cross section

If we have a capacitor with flat parallel arming, its capacitance will be given by:
C = 0,0885 [(K (s / d)], where K is the dielectric constant of the material, s the area of ​​the material in cm² and d the thickness of the insulating material in mm.
If the capacitor reinforcements are semicircular, then its capacitance will be given by:
C = 0,0885 {K [(r²²-r²²) / d]}, where K is the dielectric constant of the insulating material, d the thickness of the insulating material in mm and r1, r2 the radii of the semicircular reinforcements of the capacitor.
If the capacitor uses coaxial parallel cylinders then its capacitance will be given by:
C = 0,242 K l / log (r1 / r2), where l is the length of the cylinders in cm.

 

 

Capacitor behavior in continuous and alternating current

The capacitor in a DC circuit creates a power failure in the circuit, except for its initial charging time. In an AC circuit, the capacitor is charged and discharged according to the direction of the current and projects a resistor called capacitance resistor Xc. The capacitance Xc depends on the capacity of the capacitor and the frequency of the alternating current and is given by the relation:
Xc = 1 / 2πFC, where π = 3,14, F is the current frequency in Hz, and C is the capacity of the capacitor in Farad.

 

 

Characteristics of Capacitors

  • (A) Nominal capacity: It is the capacity for which a computer is built and a capacitor is built in a specific range of operating temperatures and frequencies. Capacitive values ​​are standardized and for intermediate values ​​the connection is calculated.
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  • (B) Capacity tolerance: The value of the nominal capacity is the ideal value for which the capacitor is built. In practice, however, there is a very small slip of the nominal value, either upwards or downwards, expressed as tolerance of the capacitor value. Usually tolerances in the capacitors range from ± 0.5% and ± 1% (precision capacitors), ± 2%, ± 5%, ± 10% to ± 20%.
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  • C) Operating voltage: It is the maximum voltage given by the manufacturer for the correct operation of the capacitor, which is indicated on the capacitor shell along with the nominal capacity and maximum operating temperature. The application of much higher voltage at its extremes than the maximum given by the manufacturer causes heating and destruction of its dielectric capacitor.
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  • (D) Test voltage: It is a constant voltage slightly higher than the maximum given by the manufacturer which is applied for a very short time (about 1 minute) to test the strength of the dielectric material at its manufacturing plant.
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  • (E) Reference frequency: The nominal capacity of the capacitor is given for a certain range of frequencies, because at very high frequencies a capacitor may have a large deviation of its nominal capacitance.
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  • F) Insulation resistance: The insulation resistance is the resistance between the capacitor electrodes as well as the resistance between the electrodes and the capacitor housing.

 

 

Types of Capacitors

Capacitors are divided into two categories in dielectric capacitors and electrolytic capacitors. The operating principle is the same in both capacitor classes, but they differ in their construction and how they are used. The following table shows the different capacitor categories.

Fixed Capacitors in market for use in Circuits

Non-Polarized Capacitors

Polarised Capacitors

mis Ceramic Capacitors Film Capacitors Electrolytic Capacitors Super Capacitors
Vacuum, Air, Glass, Silicium Class1 Class2 Metallized Metallized Film/Foil Aluminum Electrolytic Capacitors Tantalum Electrolytic Capacitors Niobium Electrolytic Capacitors Double Layer Capacitors Pseudo Capacitors
Activated Carbons Carbon Nanotubes (CNT), Graphene, Carbid-Derived Carbon (CDC) Carbon Aerogels Conducting Polymers Metal Oxides
Hybrid Capacitors Asymmetric Electrodes, Charge storage: Electrostatically and Electrochemically
Asymmetric Pseudo/EDLC Composite Rechargeable battery type
 
P100 X7R Paper PP Film non-solid hybrid polymer solid polymer non-solid solid MnO2 solid polymer solid MnO2 solid polymer
NP10 Z5U PET Film
N150 Y5V PEN Film
N220 X7S PPS Film
... X8R PTFE Film

 

 

Dielectric Capacitors Characteristics

Rated capacitance C: Is the theoretical capacity printed on the capacitor housing and refers to a given temperature and frequency.

Capacity tolerance: It is the percentage positive or negative deviation of the actual from the nominal capacity and given in ±%.

Rated Voltage DC, UDC: This is the maximum DC voltage that can be applied in a continuous mode at 40°C.

Category Voltage Uc: This is the maximum allowable voltage that can be applied in continuous mode and for temperatures above 40°C, and is less than Uoc. For temperatures of 40°C or less, UDC is equal to UC. The class voltage indicates the maximum AC or DC voltage or the sum of AC and must be equal or less than UC.

Rated AC voltage (AC): This is the maximum allowed AC voltage value that can be applied to a capacitor for continuous operation when frequency decreases.

Capacity change with temperature ΔC / C%: It is the percentage change of the nominal capacity for changing the temperature by ΔT. It is usually a negative number, that is, increasing the capacity decreases the capacity.

(ΔC / C)% = (ΔT . ppm/°C) / 104

Where ΔT is the temperature change in °C. If, for example, we have a 60°C change for a capacitor with a temperature factor of -750 ppm /°C, then its capacity change will be -4.5%.

Tande loss factor: equal to: tan δ = ω . ESR . C

The lower the coefficient, the better the capacitor is. Measuring accuracy should be within the range of ±10-4. This factor increases with increasing frequency. The ESR denotes the equivalent capacitance of the capacitor.

Blade temperature range: This is the range between the minimum and maximum temperatures that the capacitor is allowed to operate. This is given by manufacturers with the climate category eg. 55/125/56 which means temperature range (-55 +125)°C and for residence time at temperature and humidity for 56 days.

 

 

Paper Capacitors

These capacitors are named because they have the paper as a dielectric material. This paper is specially treated and impregnated with insulating oil, wax or paraffin to protect against moisture.

It is one of the first commercially built capacitors. The paper material is used for its general use, its special use of power capacitors and its high dielectric constant.

The first type of paper is used for low or medium power capacitors for DC and AC, the second type for high power, medium or high voltage capacitors, and the third for the same applications as the previous, but with an increased breakdown voltage as 11% thus 20% less paper is used for capacitor constructions with the same requirements.

Paper Capacitors

Paper capacitors operate at temperatures (-55 ~ +125)°C, and have tolerances of ± 5%, ± 10% and ± 2%. There are capacitance values ​​(0,5~20)μF for nominal voltages (350~800)VAC, (2~25) μF for voltages (220~800) VAC and (0,04~0,125) μF for voltages (2600 8000) VAC. They are mainly used for the corrosion of the cosφ, in antiparasitic and common ballasts, lighting, engine startup, low frequency disconnection, etc.

They generally find applications in AC. Of course, metallised paper capacitors are also produced with different properties than the previous ones. They present negligible parasitic elements compared to previous capacitors. For stresses greater than 10VDC, they "self-heal" when the metal sheet is punctured for some reason, thus increasing their lifetime.

They are used where the common paper capacitors, but mainly in A.C. However, AC voltage may be superposed in D.C. Both categories of paper capacitors are relatively inexpensive and have good capacity/cost ratio. Large sized capacitors record their data in their enclosure while the small ones follow the color code.

In the construction of the paper capacitor, the paper is wrapped in cylindrical machines and the final shape of the capacitor is completed by its sealing that protects it from moisture and the outlet of the impregnated liquid from the paper. Their capacity ranges from 1nF to 200μF. They are built at high continuous operation voltages from 50V to several KV.

 

 

Plastic Film Capacitors

The plastic film capacitors are made with their dielectric composed of various plastic materials such as polyester, polysterene, polypropylene and teflon. Thus, there are polypropylene capacitors, polyester capacitors, and so on.
Their construction is the same as the paper capacitors after winding the plastic tape and then being heated to tighten the capacitor terminals. Plastic film capacitors cover a wide range of capacities and trends.

Plastic Film Capacitors


The plastic film capacitors are classified in the following categories of capacitors depending on their dielectric with the following characteristics:

 

  • Polypropylene Capacitors (MKP): They are manufactured for temperatures ranging from -40 to + 85°C. They have higher insulation resistance than polyester capacitors, they are manufactured for voltages up to 630Vdc and can be used in high frequency circuits.
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  • Polystyrene Capacitors: Manufactured for the same temperature range as polypropylene capacitors, they have even higher insulation resistance than the previous capacitors mentioned and manufactured for operating voltages up to 500Vdc. The capacities for which they are manufactured range from 10pF to 10nF. They are used in circuits as coupling capacitors and have great stability in their capacitance.
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  • Polycarbonate Capacitors: Polycarbonate capacitors present the highest insulation resistance of all plastic film capacitors. They have a larger temperature range ranging from -55 to + 125°C. The trends for which they are built are from 160 to 400Vdc.
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  • Teflon Capacitors: Teflon capacitors have the largest range of temperatures than all plastic film capacitors. Their operating range ranges from -55 to + 200°C. They are suitable for high frequency circuits, such as transmitters, RF amplifiers, etc.
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  • Polyester Capacitors (MKT): They are manufactured for temperature ranges from -55 to + 125°C. They have high insulation resistance and are manufactured for capacities from 100pF to 2μF and voltages from 100 to 630Vdc. They are suitable for audio circuits, power supplies and general purpose circuits.
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    • (a) Value Calculation of polyester capacitor with color code: The calculation of the nominal value of a polyester capacitor is similar to the method of calculating the resistances based on the color code of the polyester thickener color chart. The polyester capacitors have 5 horizontal color strips that give us their nominal value, tolerance and maximum operating voltage. Starting from top to bottom, the first two bands give the value of the nominal capacity and the third multiplier zone in pF.
    • The fourth band gives us the tolerance of the capacitor and the latter has its maximum operating voltage. So in the next photo we see a polyester capacitor, where the first two zones are orange and the third zone is yellow. According to the above table, its nominal value will be 330,000pF or else 330nF. Its tolerance is the fourth color (white), so according to the color panel it is ± 10% and the last color (brown) gives us a maximum operating voltage of 100V.
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    • (b) Nominal value of polyester capacitor with symbolism: In the event that a polyester capacitor does not have a color code, then its value will be indicated by the symbol. That is, its value will be written in μF, followed by the letter J, K or M denoting the tolerance of the capacitor, J = ± 5%, Κ = ± 10% and Μ = ± 20%. It will then follow its Volt trend. ( Example: 0.033K 400 means value 33nF, ± 10%, 400V.)

 

 

Mica Capacitors

The mica capacitors are made of natural mica sheets, while the strip is made from processed natural mica and is the newest type of these capacitors. All types are manufactured with sheets of metal or alloy. Low capacity capacitors use a single-sheet micellar sheet with plating on both sides, while at the larger capacity a single-sided mica sheet is used. The operating temperatures are (-55 ~ +150)°C, the temperature coefficient ranges from (-50 ~ +200) ppm°C and the capacity change (-0,05 ~  -0,5)%. Available in nominal capacity 1pF ~ 1μF and voltages (100 ~ 35000) VDC.

Mica Capacitors

They are used in circuits requiring high stability at very high frequencies, in RF tuned circuits, filters etc. Typically they include the information in their envelope. Mica capacitors can be divided into two types. In the microwave sheet capacitors and the microwave capacitors. The first type uses a small surface dielectric physics, while the second type uses mica in the form of tape after proper processing. Contemporary microwave capacitors use a paper-like mica strip and use the winding technique, like paper capacitors.
 

 

 

Glass Capacitors

Glass Capacitors

The glass capacitors are made of small glass sheets and metal sheets, with a technique similar to that of the microwave capacitors. They are probably the first capacitors built (Leyden bottle). Today they supplement or replace the microwave capacitors in high frequency applications. They can work at high voltages up to 30KV, at temperatures (-55 ~ +250)°C, and have a positive temperature factor (140~150) ppm/°C. They are available at rated values ​​of 0.1pF ~ 120nF. They have very little parasitic induction, very high stability, but high cost. They are usually used in radio transmitting devices when high stability at high operating temperatures, resonant circuits, RF coupling or decoupling, etc. are required. They record the necessary data in their enclosure. Because of its dielectric glass, the capacitor has a very high operating temperature and a very high insulation resistance and is manufactured for very low capacities. They are used in high frequency circuits.

 

 

Oil Capacitors

Oil Capacitors

These capacitors exhibit thermal stability at high power, low losses, low inductance, high reliability and withstand high RMS currents or peak currents. They are used in power electronics, filters, couplings, dampers and control circuits. They exist in capacities of (4,7 ~ 220) μF, with tolerances ±5%, or ±10%, for voltages (320 ~ 2000) VDC currents (18~80) A, working at temperatures (-25 ~ +70) like the E12 series. For example we mention a capacitor with C = 15μF, tolerance ±10%, UDC = 900V, URMS = 630V, IRMS = 80A with climatic class 25/70/56, Up = 750V/μsec, ESR = 1,5mΩ, ESL = 80nH , tanδ = 0.0002 and RC> 10.000 sec. This capacitor has a resonant frequency of about 145KHz, so it is not used at high frequencies. In their enclosure are listed the necessary data such as capacity, tolerance, nominal voltage, URMS, the IRMS, the climatic category and date of manufacture.

 

 

Ceramic Capacitors

In the ceramic capacitors the dielectric is a ceramic material, such as magnesium silicon, alumina, zirconium oxide, etc. These materials are admixed with titanium, barium or calcium. The material mixture for its stabilization is baked at high temperatures and the reinforcement of the capacitor enters the ceramic material by plating. The shape of the ceramic capacitors can be tubular, spherical, in disc form,
Ceramic capacitors are used in high frequency circuits and their nominal capacities range from 0.1pF to 12μF. They are manufactured to operate at very high operating temperatures reaching the KV range.

Ceramic Capacitors

Depending on the composition of the ceramic material, materials of different properties are manufactured which are classified into categories of different destination.

Category I: These capacitors are very stable, have a low loss factor, their capacity increases slightly, depending on the applied AC voltage at their ends, and is constant in the applied DC voltage for values ​​up to nominal operating voltage. Their capacity also varies with the temperature, as shown in Figure, where P (positive), N (negative), NPO (negative-posi- tion-zero) and the number below denotes the temperature coefficient, e.g. P100 is +100ppm/°C or N150 is = -150ppm/°C. Also their capacity increases very little with their operating frequency up to 100MHz. These capacitors are used in coordinated circuits, RC circuits, couplings and disconnectors, oscillators, filters and so on. Generally in very high frequency circuits and where the change in capacity, the loss factor, stability, etc. are critical.

Category II: These capacitors are designed to couple and uncouple circuits, filters, timers, and so on. As well as for home appliances, radio, TV, Video, generally where the ΔC / C% change is not critical.

Category III: These capacitors are composed of disulphide material of class II and also of a special semiconductor ceramic material. A pair of diodes in antiserum and a pair of capacitors as shown in the equivalent circuit. It is obvious that the capacitance of the capacitors depends on the applied voltage at their ends. This is why all parameters are given for a certain manufacturer. Capacity decreases and the loss factor increases with increasing frequency. A characteristic of this category is the very high capacity in a very small volume of dielectric material. Ceramic capacitors can be found at: Filters, resonant circuits, coupling or decoupling, voltage amplifiers, circuits or general applications.

 

 

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