what are the factors we should check before selecting a capacitor

What are the Factors We Should Check Before Selecting a

Capacitor

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Introduction:


Capacitor

Capacitor plays a vital role in the present electronic world. Every device requires capacitors. Choosing the type of capacitor is also very important, as it is available for in different forms and with different ratings.

The advanced capacitors, what we are using now was developed in 1957 by the scientist named H. Becker. In the process of development, each capacitor had played a significant role in the electronic world.

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CapacitorWhat is a Capacitor?

Capacitor belongs to the passive element system.

It stores electric charge temporarily and statically as a static electric field.

It is of two plates which are parallel conducting plates and separated by no conducting plates i.e. A region which is called dielectric.

It will be ceramic, aluminium, air, vacuum, etc.

The capacitor formula is represented by

C = EA/d







CapacitorCharging a Capacitor Dielectric plays a key role in categorizing the capacitors. The factors to be

considered are

o Operating voltage

o Size

o Leakage resistance

o Allowable tolerance, stability

o Prices

If a higher value of capacitance (C) is required than the increase in the cross-sectional area of dielectric or to reduce the distance of separation or to use dielectric material with stronger Permittivity.







CapacitorTypes of Capacitors

The various types of capacitors are:

o Paper Capacitor

o Ceramic Capacitor

o Electrolyte Capacitor

o Polyester Capacitor

o Poly Carbonate Capacitors

o Variable Capacitor







CapacitorPaper Capacitor

It is the simplest form of capacitors.

A waxed paper is kept between two aluminium foils i.e. Sandwiched.

Cover the aluminium foil with a waxed paper.

Again cover this waxed paper with another foil.

Now, roll up this as a cylinder. P

Put two metal caps at both ends of the roll.







Capacitor

This whole assembly is set to be enclosed in a case.

By the process of rolling it, a large cross-sectional area of capacitor assembled in a reasonably smaller space.

Paper Capacitor







CapacitorCeramic Capacitor It is quite simple in construction in ceramic capacitor.

Between two metal discs a one thin ceramic disc is placed.

These terminals are soldered to the metal discs.

Everything is coated with an insulated protective coating.







CapacitorElectrolyte Capacitor Electrolyte Capacitor is used for very large values of capacitance which

can be easily achieved by this type of capacitor.

It will not only suffer from high leakage current but also working voltage level of this electrolyte capacitor is low.

The use of electrolyte in capacitor it will be polarized, which is the main disadvantage.







CapacitorElectrolyte Capacitor To make an electrolyte capacitor a tantalum oxide film.

A few micrometer thickness of aluminium oxide is used as a dielectric.

Here the capacitor value will be very high as the dielectric will be so thin.

This is because; thickness of the dielectric is inversely proportional to the capacitance.

The working voltage of the device is reduced.

A special case of electrolytic capacitor is Tantalum.







CapacitorElectrolyte Capacitor

S.no Material Dielectric Constant

Dielectric Strength Volts/.001 Inche

1 Air 1 80

2 Mica 4-8 1800

3 Porcelain 5 750

4 Paper (Oiled) 3-4 1500

5 Glass 4-8 200

6 Titanates 100-200 100







CapacitorPolyester Capacitor

Polyester capacitor is also called as Mylar PET.

It provides an ideal solution to the requirement of numerous capacitors.

Polyester film for the dielectric is placed in between the two capacitor plates.

The polyester dielectric based on chemical esters.

Polyesters include both synthetic materials and naturally occurring.







CapacitorPolyester Capacitor







CapacitorPolyester Capacitor The summary of properties of polyester capacitor Dielectric

S No Property Value

1 Temperature coefficient (ppm/oC) +400_+200

2 Capacitance drift 1.5

3 Dielectric constant (@ 1MHz) 3.2

4 Dielectric absorption (%) 0.2

5 Dissipation factor 0.5

6 Insulation resistance (MΩ x µf) 25000

7 Maximum temperature (oC) 125







CapacitorPolyester capacitor applications include

It handles high peak current levels.

De- coupling and coupling applications and DC blocking.

Polyester capacitor filters the high tolerance levels where it is not required.

It is used in Audio applications.

Power is supplied to very high capacitance level of electrolytic capacitors where it is not needed.







CapacitorPolycarbonate Capacitor

Its dielectric material is very stable.

Polycarbonate capacitor will have a high tolerance.

It can operate from a temperature of range -55°C to +125°C.

The dissipation factor and insulation resistance are good.

These capacitors belongs to a group of thermoplastic polymer.

Polycarbonate capacitor is very stable and offers the possibility of high tolerance capacitors which can be used for any temperature range.








The Properties of Polycarbonate are

S No Parameter Value

1 Volume resistivity Ωcm

2 Water absorption 0.16%

3 Dissipative factor 0.0007 @ 50Hz

4 Dielectric strength 38 kv/mm

5 Dielectric constant 3.2








Polycarbonate Capacitor Applications

o It is used as a filter, timing and precision for coupling application.

o Precision capacitors where it is needed (less than ±5%).

o Used for AC applications.







CapacitorVariable Capacitor

In a variable capacitor the capacitance may be repeated and intentionally changed electronically or mechanically.

The Variable capacitors used mostly in LC circuits which set the resonance frequency.

Variable capacitor is used in tuning the radio.

It is also called as tuning condenser or tuning capacitor or as variable reactance.

It is also used for impedance matching in antenna tuners.







CapacitorVariable Capacitor







CapacitorThe factors to be looked at before choosing a capacitor are

Stability: The value of the capacitor changes with the time and temperature.

Cost: It should be economical

Precision: +/- 20% is not common

Leakage: Dielectric will have some resistance and will leak for DC current.

The Target PF and current Power Factor at site

The Average & Maximum Demand in KVA or KW at the proposed site of installation

Nature of Load of the Site.

The availability of space at the site of installation, power cables etc.







CapacitorThe Capacitor Tolerance

Code ToleranceB ± 0.1 pF

C ± 0.25 pF

D ± 0.5 pF

F ± 1%

G ± 2%

J ± 5%

K ± 10%

M ± 20%

Z +80%, –20%







Capacitor

The temperature coefficient of capacitance is manufactured by taking the reference of 25 degree Centigrade.

Capacitor Polarization will have polarity whereas for non polarized will not have polarity.

The Capacitor Tolerance







CapacitorGeneral uses of Capacitors It is used for smoothing in power supply applications when required to

convert the signal from AC to DC.

Signal coupling and decoupling as a capacitor coupling.

It used for electrical power factor correction.

In radio systems, LC oscillator is connected for tuning to the desired frequency.

Used for the fixed discharging and charging time of the capacitors for Storing Energy.







CapacitorGeneral uses of Capacitors

It allows an AC current to pass and blocks DC current in circuits.

The frequency of any signal you’re trying to couple or noise you’re trying to suppress.

Minimum/maximum value required.

Desirable value.

Package/lead style.








Operating/maximum voltage

Tolerance

Equivalent series resistance

Polarized ok? Or need non-polarized

Operating temperature

Tolerance including temperature coefficient

Leakage

Size requirement








Price objective

Price budget

Customer’s prejudices

Availability/lead time

Lifetime requirement

ROHS requirements

Sample availability

Tape and Reel

Manufacturer’s reputation






What are the Factors We Should Check Before Selecting

a CapacitorConclusion

Thus, this is all about a capacitor, different types of capacitors and what are the factors we should check before selecting a capacitor.

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what are the factors we should check before selecting a capacitor

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