Resistors, capacitors, inductors, relays, transformers, connectors etc. are various types of components used in electric and electronic circuits.
1. Resistors:
Resistors are those circuit elements which introduce electrical resistance into the circuit. There are many types of resistors, each one suitable for its particular application. They vary with regard to their resistance expressed in ohms, their power rating in watts, the material of the resistance element and whether they are of the fixed or variable resistance type.
Ratings of Resistors:
ADVERTISEMENTS:
The standard power ratings for resistors are 0.125, 0.25 0.5, 1, 2, 3, 4, 5, 10, 20, 25, 30, 40, 50, 75, 100, 150, 200, watts and higher.
The standard values of resistances available are:
Ohms and Kilo Ohms: 1, 1.2, 1.5, 1.8, 2.2, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, 10, 12, 15, 18, 22, 33, 39, 47, 56, 68, 82, 100, 120, 150, 180, 220, 330, 390, 470, 560, 680, 820.
Meghaohms: 1, 1.2, 1.5, 1.8, 2.2, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, 10, 12, 15, 18, 22.
ADVERTISEMENTS:
Colour Coding of Resistors:
Colour codes are used to designate the value of a resistor placed in any position in an equipment board. Rings or band of different colours are usually placed around the resistor. The colour of first three bands determine the total resistance value, while the fourth band is used to indicate tolerance as illustrated in figure 8.1 Table 8.1 gives the complete colour code of electronic resistors.
A. Determines the first digit
ADVERTISEMENTS:
B. Determines the second digit
C. Determines the number of zeroes following the first two digits.
D. Determines the tolerance.
2. Capacitors:
A capacitors is a device capable of storing an electric charge (static electricity). It consists of two metal plates separated by a dielectric material. A capacitor is designed for deliberately providing a known amount of capacitance in circuit. Capacitors are available in values ranging from less than one Pico farad to thousands of microfarads. While using a capacitor its ratings must be carefully observed to be certain that the potential to be applied across the capacitor is not greater than the rated value.
3. Inductor:
ADVERTISEMENTS:
It is an electronic component designed especially for introducing a required amount of inductance in the circuit. An inductor consists of a two-terminal, single winding wound on air or iron core. An air core inductor employs a non-magnetic core whereas an iron core may employ a magnetic material other than iron.
The unit of measurement of inductance is the henry. Inductors commonly employed in electronic circuits range in values from less than one mH to about 20 H. Small inductors are used in radio frequency tuned circuits and as radio frequency chokes. Larger inductors are employed at audio-frequency; the largest inductors are used as filter chokes in power supplies.
Construction of Inductors:
ADVERTISEMENTS:
The constructional features an inductor are determined largely by the frequency range in which it is to operate. In general, low frequency inductors have many turns and employ an iron core. In contrast high frequency inductors have fewer turns and often employ an air core. The stray capacitance between the turns and between the layers of turns is an important factor in higher frequency coils, and therefore special winding configurations may be employed to minimise this capacitance.
Current and voltage consideration also determine the constructional features of an inductor. The gauge of the wire for example, is selected in accordance with the amount of current the coil must carry. Receiver coils, which normally carry only a few mA of current, are wound from fine wires.
Transmitter coils, which normally carry much greater current, are wound using heavier wires. An inductor designed for use in high voltage circuits will have heavier insulation than the one designed for low voltage applications. Inductors may be made of iron core, powder core, ferrite core on air core depending upon the frequency range of their operation.
Iron-Core Inductors:
Low-frequency inductors are normally iron core inductors. These are generally large, both in inductance and in physical dimensions. Such inductors include filter reactors and audio frequency chokes. Low frequency iron-cored chokes are largely used to smooth out the ripple voltage in rectified ac power supplies. The core materials most commonly used are silicon-iron laminations and grain oriented silicon steel. Windings are usually of enamelled solid copper wire with interlayer insulation and impregnated with suitable material.
Power Core Inductors:
Powder core inductors are used at much higher frequencies than iron-core inductors. The techniques of reducing eddy current loss by dividing the core into smaller segments, accounts for use of the ‘powdered-iron’ core. The iron dust in these cores is often ferrite (a mixture of ferric oxide and other substances such as nickel and cobalt).
The magnetic powder is mixed with an insulating binder material so that each magnetic particle is electrically insulated from one another. The magnetic powder and insulating binder substance (usually rod shaped) are moulded to fit into the coil. This rod of core material (known as slug) is normally mounted so that it can be moved into or out of the coil, usually by means of a screw.
Ferrite Core Toroids:
A toroid is a coil wound on a round shaped solid of circular cross-section ferromagnetic core. The main advantage of the toroidal coil is that all of the magnetic flux is contained within the core material; therefore remains unaffected by surrounding components. Another advantage of toroids is that it has smaller physical size, for a given amount of inductance, than solenoid coil.
The core is usually made of ferrites. As they are electrically insulators, they do not suffer from the effect of eddy current. The toroidal winding is placed in the annular space. An air gap is introduced in the centre core and by choosing a suitable length for this gap, the properties of the core may be changed to suit a wide range of design requirements.
Air Core Inductor:
High frequency inductors, such as RF (Radio Frequency) chokes and the tank coils are generally more critical than low frequency types with respect to core-losses and stray capacitance. Iron cores are seldom used in RF inductors because the core losses would be excessive at high frequencies. At higher carrier and radio frequencies air core and powdered iron slugs are used.
4. Transformers:
Transformers are used in electronic equipments not only to step-up or step down the voltage but also to electrically isolate the electronic circuit from the mains. Transformers are made in great variety to meet application requirements.
Following types of transformers are generally used in electronic equipments:
(i) Isolation transformation;
(ii) Current transformers;
(iii) Auto transformers;
(iv) Pulse transformers;
(v) Audio transformers;
(vi) Radio-frequency transformers;
(vii) Intermediate frequency transformers;
(viii) Rectifier transformers;
(ix) Constant voltage transformers.
5. Relays:
A relay is a device that functions as an electrically operated switch. Relays are used to open or close the contacts in the circuits. The contacts may be either in the same circuit as the operating signal or in another circuit or combination of circuit. Relays are widely used in industrial applications. When the coil of a relay is energised or de-energised, its contacts are On or OFF. Various types of relays are available in the market. The selection of a particular relay depends on the type of application.
6. Connectors:
Connectors are usually described as a piece of equipment used in joining two pieces of electronic equipment. There are many types of connectors available in the market.
Various types of connectors used in electronic equipments are:
(i) Audio connectors
(ii) RF connectors
(iii) PC board connectors
(iv) Standard rack and panel connectors
(v) Standard threaded circular connectors.