How To Select Capacitors Types Based On Different Priorities

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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
Introduction

• 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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What are the Factors We Should Check Before
Selecting a Capacitor
What 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

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What are the Factors We Should Check Before
Selecting a Capacitor
Charging a Capacitor

• Dielectric plays a key role in categorizing the
  capacitors. The factors to be considered are

• Operating voltage
• Size
• Leakage resistance
• Allowable tolerance, stability
• 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Types of Capacitors

• The various types of capacitors are

• Paper Capacitor
• Ceramic Capacitor
• Electrolyte Capacitor
• Polyester Capacitor
• Poly Carbonate Capacitors
• Variable Capacitor

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What are the Factors We Should Check Before
Selecting a Capacitor
Paper 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.
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What are the Factors We Should Check Before
Selecting a Capacitor
Paper 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Ceramic 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Electrolyte 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Electrolyte 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. 

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What are the Factors We Should Check Before
Selecting a Capacitor
Electrolyte 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
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What are the Factors We Should Check Before
Selecting a Capacitor
Polyester 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Polyester Capacitor
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What are the Factors We Should Check Before
Selecting a Capacitor
Polyester 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 (_at_ 1MHz) 3.2
4 Dielectric absorption () 0.2
5 Dissipation factor 0.5
6 Insulation resistance (M? x µf) 25000
7 Maximum temperature (oC) 125
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What are the Factors We Should Check Before
Selecting a Capacitor
Polyester 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Polycarbonate Capacitor

• Its dielectric material is very stable.
• Polycarbonate capacitor will have a high
  tolerance.
• It can operate from a temperature of range -55C
  to 125C.
• 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Polycarbonate Capacitor
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What are the Factors We Should Check Before
Selecting a Capacitor
Polycarbonate Capacitor
The Properties of Polycarbonate are
S No Parameter Value
1 Volume resistivity ?cm
2 Water absorption 0.16
3 Dissipative factor 0.0007 _at_ 50Hz
4 Dielectric strength 38 kv/mm
5 Dielectric constant 3.2
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What are the Factors We Should Check Before
Selecting a Capacitor
Polycarbonate Capacitor

• Polycarbonate Capacitor Applications

• It is used as a filter, timing and precision for
  coupling application.
• Precision capacitors where it is needed (less
  than 5).
• Used for AC applications.

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What are the Factors We Should Check Before
Selecting a Capacitor
Variable 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
Variable Capacitor
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What are the Factors We Should Check Before
Selecting a Capacitor
The 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
The Capacitor Tolerance
Code Tolerance
B 0.1 pF
C 0.25 pF
D 0.5 pF
F 1
G 2
J 5
K 10
M 20
Z 80, 20
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What are the Factors We Should Check Before
Selecting a Capacitor
The Capacitor Tolerance

• 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
General 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.

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What are the Factors We Should Check Before
Selecting a Capacitor
General uses of Capacitors

• It allows an AC current to pass and blocks DC
  current in circuits.
• The frequency of any signal youre trying to
  couple or noise youre trying to suppress.
• Minimum/maximum value required.
• Desirable value.
• Package/lead style.

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What are the Factors We Should Check Before
Selecting a Capacitor
General uses of Capacitors

• Operating/maximum voltage
• Tolerance
• Equivalent series resistance
• Polarized ok? Or need non-polarized
• Operating temperature
• Tolerance including temperature coefficient
• Leakage
• Size requirement

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What are the Factors We Should Check Before
Selecting a Capacitor
General uses of Capacitors

• Price objective
• Price budget
• Customers prejudices
• Availability/lead time
• Lifetime requirement
• ROHS requirements
• Sample availability
• Tape and Reel
• Manufacturers reputation

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What are the Factors We Should Check Before
Selecting a Capacitor
Conclusion

• 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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