FAMILIARIZATION AND IDENTIFICATION OF ELECTRONIC COMPONENTS WITH SPECIFICATION (contd)
Capacitors are generally classified as fixed and
variable.
1.2.1. FIXED CAPACITORS
In Fixed capacitors whose value cannot be changed. According to the
dielectric material used in construction of the capacitors, they are named
i) Paper capacitor
ii) Mica capacitor
iii) Ceramic capacitor
iv) Plastic (Polyester capacitor)
v) Electrolytic capacitor
i)
PAPER CAPACITOR
ii) Mica Capacitors
iii)
CERAMIC CAPACITORS
Ceramic capacitors are also called as
Disc-capacitors. These are also the mostly used type of capacitors. A ceramic
capacitor is constructed with two or more alternating layers of ceramic and a
metal. Here the ceramic acts as its dielectric and metal acts as its
electrodes. These ceramic capacitors are non-polarized fixed type capacitors.
v)
ELECTROLYTIC CAPACITORS
1.2.2. VARIABLE CAPACITORS
A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically.
i) AIR GANG CAPACITOR
Gang capacitor is a group of capacitors ganged together the dielectric is air. It is a stator rotor type variable capacitor which consists of two sets of metal plates. The fixed plates are connected together to form the stator. The movable plates are connected together on a shaft shaft to form rotor. By rotating the shaft change the common area between the plates thus the capacitance is varied.
ii) TRIMMER CAPACITOR
In trimmer capacitor two plates separated by a sheet of mica. A screw adjustment is used to vary the distance between the plates, thereby changing the capacitance.
An inductor is a passive electronic component that stores energy in the form of a magnetic field. In its simplest form, an inductor consists of a wire loop or coil. Inductance is the property of inductors by which it opposes any change in the current flow through it.
The specifications of inductors are:i) Inductance value ii) Current rating.
This type of inductor is made from thin copper wire wound over a former made of thick card board. It has low value of inductance.
This type of inductor is made of copper wire wound on a laminated iron core. Laminated iron core is used to avoid the eddy current losses. Laminated core consists of thin iron sheets pressed together and insulated from each other
In this type, a coil of wire is wound on a solinoid core made of ferromagnetic material called ferrite. It is used for its properties of high magnetic permeability coupled with low electrical conductivity which helps prevent eddy currents
Probably the most common type of variable inductor today is one with a moveable ferrite magnetic core, which can be slid or screwed in or out of the coil. Moving the core farther into the coil increases the permeability, increasing the magnetic field and the inductance. Many inductors used in radio applications (usually less than 100 MHz) use adjustable cores in order to tune such inductors to their desired value.
The transformer transfer energy from one coil to another through magnetic flux linkage. Basically a transformer a transformer consists of two or more coils wounded on the same core placed close enough so that magnetic lines of force from one coil will cut the turns of other coil. The coil which input voltage applied is called primary winding and the coil in which the voltage induced due to changing magnetic flux is called the secondary winding.
Specifications of transformers are
i) voltage rating ii) current rating iii)power rating iv) frequency range
They are mainly used as step up and step down transformers. They are designed to handle large power. The materials used for core of these transformers are laminated iron or silicon steel. In step up transformer number of turns in the secondary is more than that in the primary and vice versa for step down transformer. Step down transformers are extensively used in DC power supplies.
The design of high frequency circuits is comparatively difficult. So, in radio receivers, radio frequencies are reduced to lower frequency called intermediate frequency. Intermediate frequency transformer (IFT) is a device that tunable to IF. The standard IF in radio reception is 455kHz. IFT is designed to respond this frequency only. This achieved by using parallel capacitors across primary and secondary windings. The assembly of IFT enclosed in an Aluminium can includes a capacitance of 40pf and an inductance of 3mH.
These transformers are used in AF applications for voltage, current and impedance transformation. Input output transformers are the popular name for the AF transformers. Input transformers are used to couple a low impedance source such as microphone with a high impedance circuit like amplifiers. Output transformers are used in PA system, radio receivers etc., to match the high output impedance of an amplifier with loud speaker having low impedance.
A pulse transformer is a transformer that is optimised for transmitting rectangular electrical pulses constant amplitude. Pulse transformers are widely used in power circuits for isolate between low power and high power circuits. Example SCR triggering circuits.
1.2 CAPACITORS
The
capacitor is a component which has the ability or capacity to store energy in
the form of an electrical charge producing a potential difference (Static
Voltage) across its plates. A Capacitor consists of two or more parallel
conductive (metal) electrically separated either by air or by some form of a
good insulating material.The insulating layer between a capacitor plates is
commonly called the Dielectric.
The capacitance is a measure of capacitors.
The important specification of capacitors in practical case
are
i)
Capacitance value
ii)
Voltage rating.
Capacitors are generally classified as fixed and
variable.
1.2.1. FIXED CAPACITORS
In Fixed capacitors whose value cannot be changed. According to the
dielectric material used in construction of the capacitors, they are named
i) Paper capacitor
ii) Mica capacitor
iii) Ceramic capacitor
iv) Plastic (Polyester capacitor)
v) Electrolytic capacitor
 |
| Symbol of Fixed Capacitor |
i)
PAPER CAPACITOR
This type of capacitor is made between two metal
foils. By this arrangement, a large plate area can be concentrate in a small
volume and hence high capacitance value.
ii) Mica Capacitors
- This type of capacitors consists of a number of flat strips of metal foil separated by similar shaped mica strips. Mica acts as the die electric. Alternate plates are connected together. Thus two sets ate formed. Each sets of plates is attached lead wire. The entire unit is encapsulated using an insulating case
iii)
CERAMIC CAPACITORS
Ceramic capacitors are also called as
Disc-capacitors. These are also the mostly used type of capacitors. A ceramic
capacitor is constructed with two or more alternating layers of ceramic and a
metal. Here the ceramic acts as its dielectric and metal acts as its
electrodes. These ceramic capacitors are non-polarized fixed type capacitors.
iv)
POLYESTER CAPACITOR
Polyester capacitors are based around the use of a polyester
dielectric. It consist of two metal foil separated by a strip of
polyester material such as Mylar. The electrodes of film capacitors may be metallized aluminum or zinc applied directly to the surface of the
plastic film, or a separate metallic foil overlying the film. Each metal film
or foil is connected to a lead which extends either axially or radially from the capacitor and encased in glass or ceramic container.
v)
ELECTROLYTIC CAPACITORS
Electrolytic
Capacitors are generally used in the applications where very large
capacitance values are required. The electrolytic capacitors have a metallic
anode covered with an oxidized layer generally used as its dielectric. Another
electrode of a capacitor is a non-solid or solid electrolyte. Most of the
electrolytic capacitors are polarized. These capacitors are categorized
according to their dielectric material. Mainly these are categorized in to
three classes, they are given as
·
Aluminium
electrolytic capacitors: Here aluminium acts as its dielectric.
·
Tantalum electrolytic capacitors:
Here tantalum pent oxide acts as its dielectric.
·
Niobium electrolytic
capacitors:Here niobium pent oxide acts as its dielectric
A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically.
i) AIR GANG CAPACITOR
Gang capacitor is a group of capacitors ganged together the dielectric is air. It is a stator rotor type variable capacitor which consists of two sets of metal plates. The fixed plates are connected together to form the stator. The movable plates are connected together on a shaft shaft to form rotor. By rotating the shaft change the common area between the plates thus the capacitance is varied.
 |
| Gang capacitor with symbol |
ii) TRIMMER CAPACITOR
In trimmer capacitor two plates separated by a sheet of mica. A screw adjustment is used to vary the distance between the plates, thereby changing the capacitance.
1.3. INDUCTORS
An inductor is a passive electronic component that stores energy in the form of a magnetic field. In its simplest form, an inductor consists of a wire loop or coil. Inductance is the property of inductors by which it opposes any change in the current flow through it.
The specifications of inductors are:i) Inductance value ii) Current rating.
The values of inductors will be written on it. Inductors may be classified as fixed and variable types.
i) FIXED INDUCTORS
Based on the type of core material used fixed inductors may be classified as air core, iron core and Ferrite core inductors.
a) AIR CORE INDUCTORS
This type of inductor is made from thin copper wire wound over a former made of thick card board. It has low value of inductance.
 |
| Air core Inductor |
b) IRON CORE INDUCTOR
This type of inductor is made of copper wire wound on a laminated iron core. Laminated iron core is used to avoid the eddy current losses. Laminated core consists of thin iron sheets pressed together and insulated from each other
 |
| iron core inductor |
c) FERRITE CORE INDUCTOR
In this type, a coil of wire is wound on a solinoid core made of ferromagnetic material called ferrite. It is used for its properties of high magnetic permeability coupled with low electrical conductivity which helps prevent eddy currents
 |
| Ferrite core Inductor |
ii) VARIABLE INDUCTOR
Probably the most common type of variable inductor today is one with a moveable ferrite magnetic core, which can be slid or screwed in or out of the coil. Moving the core farther into the coil increases the permeability, increasing the magnetic field and the inductance. Many inductors used in radio applications (usually less than 100 MHz) use adjustable cores in order to tune such inductors to their desired value.
1.4. TRANSFORMERS
The transformer transfer energy from one coil to another through magnetic flux linkage. Basically a transformer a transformer consists of two or more coils wounded on the same core placed close enough so that magnetic lines of force from one coil will cut the turns of other coil. The coil which input voltage applied is called primary winding and the coil in which the voltage induced due to changing magnetic flux is called the secondary winding.
Specifications of transformers are
i) voltage rating ii) current rating iii)power rating iv) frequency range
i) POWER TRANSFORMER
They are mainly used as step up and step down transformers. They are designed to handle large power. The materials used for core of these transformers are laminated iron or silicon steel. In step up transformer number of turns in the secondary is more than that in the primary and vice versa for step down transformer. Step down transformers are extensively used in DC power supplies.
ii) INTERMEDIATE FREQUENCY TRANSFORMER (IFT)
The design of high frequency circuits is comparatively difficult. So, in radio receivers, radio frequencies are reduced to lower frequency called intermediate frequency. Intermediate frequency transformer (IFT) is a device that tunable to IF. The standard IF in radio reception is 455kHz. IFT is designed to respond this frequency only. This achieved by using parallel capacitors across primary and secondary windings. The assembly of IFT enclosed in an Aluminium can includes a capacitance of 40pf and an inductance of 3mH.
iii) AUDIO FREQUENCY TRANSFORMER
These transformers are used in AF applications for voltage, current and impedance transformation. Input output transformers are the popular name for the AF transformers. Input transformers are used to couple a low impedance source such as microphone with a high impedance circuit like amplifiers. Output transformers are used in PA system, radio receivers etc., to match the high output impedance of an amplifier with loud speaker having low impedance.
iv) PULSE TRANSFORMER
A pulse transformer is a transformer that is optimised for transmitting rectangular electrical pulses constant amplitude. Pulse transformers are widely used in power circuits for isolate between low power and high power circuits. Example SCR triggering circuits.
 |
 |
| Power transformer and symbol |
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