what's a capacitors

8/8/2019 What's a Capacitors

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Profile of Capacitors

This is what a capacitor is.

You may already know these facts, but let us still explain capacitors and theirprinciple of operation for those who may not know.

Capacitors store electricity and

block the flow of DC.

Capacitors have two main features. One of which is

a function to charge or discharge electricity. This

function is applied to smoothing circuits of power

supplies, backup circuits of microcomputers, andtimer circuits that make use of the periods to charge

or discharge electricity. The other is a function to

block the flow of DC. This function is applied to

filters that extract or eliminate particular frequencies.This is indispensable to circuits where excellent

frequency characteristics are required.

Condensers vs. Capacitors

The name "capacitor" was given in the US due to itscapacity for charging electricity. When capacitors

were introduced to Japan, the English word

"capacitor" was translated as "chikudenki," which

means a component that can condense and storeelectricity. Later, people in Japan thought it was

called condenser in the US when they retranslated it

into English. That is the reason the electric

component called capacitor in the US is still calledcondenser in Japan.

Moreover, in another theory it used to be called the

"condenser" in the world, but recently there is also

an opinion of having came to be called "capacitor".


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Main Applications of Capacitors

AC ----------> The smoothing circuit works incombination with the diode rectifier

circuit.

----------> DC

Pulse ----------> The t imer circuit makes use of the time

required for the capacitor to charge

electricity.

----------> A time

lag is

caused.

Mixed

signals

----------> The low-pass filter combines the

capacitor and resistor.

----------> Only the

desired

low-

frequencysignal is

obtained.


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Mixed

signals

----------> The high-pass filter combines the

capacitor and resistor.

----------> Only the

desiredhigh-

frequencysignal is

obtained.


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Glossary

The following provides information on main capacitor terms.

Capacitance If voltage is applied to the two flat metal plates thatare located in parallel to each other as shown in Fig.

1, electricity is charged by the plates. Capacitors

make use of this phenomenon. The electrostaticcapacity of a capacitor indicates the amount of

electric energy the capacitor can charge. The larger

the plates are, the higher the electrostatic capacity is,

and the shorter the distance between the plates is, the

higher the electrostatic capacity is.

Dielectric Constant Usually, the two electrode plates of a capacitor areseparated with an electrolyte, ceramic, or plastic film

as a dielectric. Capacitors are classified according to

the difference in dielectric (e.g., electrolytic

capacitors and ceramic capacitors). The electrostaticcapacity of a capacitor varies with the dielectric even

though there is no difference in electrode plate size or

plate-to-plate distance. The dielectric constant K is

determined by the dielectric.

C: CapacitanceK: Constant (Dielectric constant)

S: Electrode plate size (area)

d: Distance between two electrodeplates

F: Farad (a unit of electrostatic

capacity)


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Glossary

Dielectric loss tangent (tan ) The electrostatic capacity of a capacitor is obtainable

from the above-mentioned equation. A capacitor inactual use causes loss due to the dielectric

polarization of the capacitor and the inductance ofthe lead wires of the capacitor. The rate of this loss

is called dielectric loss tangent and expressed inpercentage. In the following equation, Q indicates

the quality of the capacitor. The larger the Q is, the

higher the quality is.

Insulation resistance (IR) The two electrode plates of a capacitor are separatedfrom each other. Theoretically, the resistance

between the two electrode plates should be infinite.

There is, however, a minute current flow between

the electrode plates in actual operation. Therefore,the resistance between the electrode plates is not

infinite. This resistance is called insulation resistance

and usually expressed in M .

Equivalent serial resistance(ESR)

There is resistance between the two electrode platesof any capacitor. If a capacitor handles high-

frequency signals, this resistance has a great

influence on the performance of the capacitor. This

resistance is called equivalent serial resistance (ESR)and usually expressed in m .


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Outline of a Capacitor

2. A variety of capacitors and their features

Type Feature Application circuit

Multi-layered

ceramiccapacitor

This type of capacitor has been developed to

meet demands for high -density ceramiccapacitors. Mult i-layered ceramic capacitors

incorporate multiple printed layers of electrode

plates made of 10 to 20m thick ceramic sheets.

These capacitors are more compact and havebetter temperature characteristics than single -

layered ceramic capacitors. Multi-layered

ceramic capacitors are, however, rather

expensive because their electrode plates use

precious metals. With the further developmentof materials for electrode plates, these

capacitors are expected to take the lead in the

main stream of ceramic capacitors. Like asingle-layered ceramic capacitor, a multi-layered ceramic capacitor is either a product of

high dielectric constant construction or a

product that has excellent temperature

characteristics ideal for temperaturecompensation.

Circuits of general

electronic equipment

Single-layered

ceramiccapacitor

This type of capacitor that incorporates a

ceramic dielectric is either a product ideal for

temperature compensation, a product that has ahigh dielectric constant, or a product that is of a

semiconductor type, which depends on the kind

of ceramic dielectric. The single-layered

ceramic capacitor for temperature compensationdoes not have a high electrostatic capacity but it

covers a wide temperature characteristic range

including temperatures below 0C. The

capacitor of high dielectric constantconstruction is compact yet it has a high

electrostatic capacity. The semiconductor type

capacitor is far more compact yet it has the

highest electrostatic capacity of all single -layered ceramic capacitors.

Circuits that require

excellent frequency

characteristics, suchas high-frequency

circuits and digital

circuits


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Film

capacitor

The high-frequency and temperature

characteristics of film capacitors excel those of

ceramic capacitors. Furthermore, high-capacityfilm capacitors are available, which are,

however, more expensive and larger than

ceramic capacitors that are the same in capacity.

Polyester (Myler), polypropylene, orpolystyrene can be used for the film of this type

of capacitors.

High-frequency

circuits and analog

circuits

Metal-glazed

film capacitor

This type of capacitor incorporates electrode

plates made of film vacuum-evaporated with

metal such as aluminum. Metal-glazed film

capacitors can be more compact yet higher inelectrostatic capacity than film capacitors.

Polyester, polypropylene, or polycarbonate can

be used for the film of this type of capacitors.

High-frequency

circuits, switching

circuits, and analog

circuits

Aluminum

electrolyticcapacitor

This type of capacitor incorporates a metaloxide film dielectric produced from electrolysis

and its anode is made of aluminum. That is the

reason this type of capacitor is called aluminum

electrolytic capacitor. It is possible to producehigh-capacity aluminum electrolytic capacitors.

Their frequency and temperature characteristics

are, however, bad.

Power supplycircuits, audio

circuits, timer

circuits, and backup

circuits

Tantalumelectrolytic

capacitor

This type of capacitor is similar to aluminumelectrolytic capacitors, but its anode is made of

tantalum instead of aluminum. Tantalum

electrolytic capacitors are a little inferior in

electrostatic capacity to aluminum electrolytic

capacitors. The frequency and temperaturecharacteristics of tantalum electrolytic

capacitors, however, excel those of a luminum

electrolytic capacitors.

Noise limiters,coupling circuits,

and filter circuits

Others

Mica, glass, and paper are used for dielectricelements as well as the materials described

above. Mica is the best dielectric but it is

expensive. Glass ensures a stable temperature

coefficient in a wide range. Paper is used forhigh-voltage capacitors.

Precision equipmentand high-voltage

equipment


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3. Frequency

characteristicsof each type of

capacitor

If the impedance of a capacitor dropped in proportion to an increase

in frequency rectilinearly, it would be an ideal capacitor. Thefollowing graph indicates how the actual impedance of each type of

capacitor drops due to the res istance of the capacitor as the frequencyrises. The change in the impedance varies with the construction and

material of the capacitor. It is possible to say that the lower theresistance of the capacitor when the capacitor resonates (i.e., point a

in the graph below) is, the better the frequency characteristics of the

capacitor are. From this graph, you will know that ceramic and film

capacitors are suitable for high-frequency circuits.

4. Insulation

resistanceof each type of

capacitor

If the insulation resistance of a capacitor did not change with the

ambient temperature, it would an ideal capacitor. The following graphindicates that the insulation resistance of each type of capacitor

decreases as the temperature rises. The value of insulation resistance

at indoor temperature varies with the capacitor. Each capacitor,

however, has a general tendency to decrease its insulation resistance

when the ambient temperature exceeds 25C. There is only a littledifference between the slopes of insulation resistance, although the

Myler film capacitor has a little greater decrease in insulationresistance and the ceramic capacitor for temperature compensation

has a comparatively small decrease and so does the mica capacitor.


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5. Dielectric loss

tangent (tan)

of each typeof capacitor

The dielectric loss tangent (tan ) of a capacitor indicates the

dissipation of the capacitor. Therefore, it would be ideal if this valuewere 0% at all temperatures. From the following graph, you will

know that the dielectric loss tangent (tan ) of the ceramic capacitorfor temperature compensation and that of the mica capacitor are

rather small, and therefore, they have better characteristics with onlya little dissipation.

6. Operating

temperaturerange

of each type

of capacitor

If the electrostatic capacity of a capacitor did not change in a wide

temperature range as shown as the straight line marked "1" in thefollowing graph, the temperature characteristics of the capacitor

would be ideal. Practically, the electrostatic capacity greatly varies

with the temperature. From the graph, you will know that the ceramic

capacitor for temperature compensation has the best temperaturecharacteristics, followed by the film capacitor, mica capacitor, and

tantalum capacitor. The ceramic capacitor of high dielectric constant

construction shows an extraordinary curve. Utmost attention is

required when using this type of capacitor.


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7. Electrostatic capacity range

of each type of capacitor

[100 F or more]

Tantalum electrolytic capacitors as well asaluminum electrolytic capacitors cover this range.

Smoothing circuits of power supplies and emittercapacitance and coupling capacitance purposes in

audio circuits.

[10 to 100 F]

Tantalum electrolytic capacitors as well as

aluminum electrolytic capacitors cover this range.Tantalum electrolytic capacitors are, however, so

expensive that they are used for applications to

which their particular characteristics are essential.

[1 to 10 F]Ceramic capacitors of high dielectric constant

construction as well as aluminum electrolytic

capacitors and tantalum electrolytic capacitorscover this range. These capacitors are used for awide range of application including timer circuits

and filter circuits.

[0.1 to 1 F]Most capacitors cover this range. Especially, film

capacitors and ceramic capacitors of high dielectric

constant construction are ideal. These capacitors

are often used as bypass capacitors for ICs.

[0.01 to 0.1 F]

Ceramic capacitors and film capacitors cover this

range. Especially, these capacitors are often usedfor higher-frequency applications.

[1,000 to 10,000 pF]

Ceramic capacitors and film capacitors cover thisrange. Mainly, these capacitors are used for signal

processing circuits, such as filter circuits.

[100 to 1,000 pF]Ceramic capacitors for temperature compensation

cover this range. These capacitors are used for


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high-frequency applications, such as filter circuits.

[10 to 100 pF]Ceramic capacitors for temperature compensation

are used for high-frequency filter circuits and phase

compensation for bypass amplifiers of high-

frequency oscillators.

[1 to 10 pF]Ceramic capacitors are used for phase

compensation for higher-frequency amplifiers.


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8. Rated voltage

of each type of capacitor

The rated voltage of a capacitor means the highest

permissible voltage applicable to the electrodeplates of the capacitor. Working voltage (WV) or

voltage (V) is used as a unit to express the ratedvoltage of each capacitor. The value of rated

voltage varies with the capacitor. A capacitor isusually used with 1/2 or less of the rated voltage by

taking the surge voltage on the capacitor into

consideration.

[Aluminum electrolytic capacitors]

Usually 6.3, 10, 16, 25, 35, 50, or 100 V. The

number of low-capacity, low-voltage aluminum

electrolytic capacitors produced is not large. High-capacity, high-voltage products are available by

order.

[Tantalum electrolytic capacitors]Usually 6.3, 10, 16, 25, or 35 V.

[Single-layered ceramic capacitors]

Usually 50 or 500 V. High-voltage products are,however, manufactured.

[Multi-layered ceramic capacitors]

Usually 25 or 50 or 16 V. The availability of 10-Vproducts depends on the series of models.

[Film capacitors and metal-glazed film capacitors]

Low voltage (50 or 500V) and high voltage (250,400, or 630 V).

[Others]

Mica, glass, and paper capacitors are of highdielectric constant construction. Therefore, these

capacitors with high dielectric strength are

available.


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Profile of Multi-

layered CeramicCapacitors

What is a Multi-

layered CeramicCapacitor?

Let us know the history and basic construction of multi-layered

ceramic capacitors.


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Multi-layered

Ceramic

Capacitor Map


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Born in the US in the 40's The multi-layered ceramic capacitor was invented in

the US in the forties based on conventional materialsfor single-layered ceramic capacitors and baking

technologies. Due to its compactness, highcapacitance, and high reliability, this type of capacitor

was mainly used for military purposes in those days.The multi-layered ceramic capacitor did not become

popular until the sixties. Recently, the multi-layered

ceramic capacitor has been making remarkable

progress and playing an important role in a variety offields by keeping in step with the development of

hybrid ICs, computers, and ultraminiature electronic

equipment.

Multi-layered construction i sthe secret ensuring

compactness and high capacity

As shown in the following illustration, the multi-layered ceramic capacitor incorporates multiple layers

consisting of thin dielectric elements, thus making itselectrostatic capacity as high as possible for its size.

what's a capacitors

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