Electronic component

Transcription

1 Electronic component

2 Electronic component: An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. 2

3 TYPES OF COMPONENTS PASSIVE COMPONENTS: Components capable of dissipation and storage of energy. They do not require external source for their operation. Eg: Resistors, Capacitors, Inductors etc ACTIVE COMPONENTS: The components in which transformation of Energy takes place They are having the capability of processing a signal its own. They need external source for their operation. They have power gain Eg: Diode, Transistors etc 3

4 RESISTOR: 4

5 Resistor: It is an electrical device whose primary function is to introduce resistance to the flow of electric current. The magnitude of opposition to the flow of current is called the resistance of the resistor. The basic functions of resistors are 1. To restrict the current flow 2. To produce a voltage drop 3. To divide the voltage 5

6 The resistance of a resistor is directly proportional to the resistivity of the material and the length of the resistor and inversely proportional to the cross-sectional area perpendicular to the direction of current flow. The resistance R of a resistor is given by R= ρl/a where r is the resistivity of the resistor material (W cm), l is the length of the resistor along direction of current flow (cm), A is the cross-sectional area perpendicular to current flow (square cm) Resistivity is an inherent property of materials. 6

7 The resistance of a resistor can be defined in terms of the voltage drop across the resistor and current through the resistor related by Ohm s law, R = V I where R is the resistance (W), V is the voltage across the resistor (V), and I is the current through the resistor (A). Whenever a current is passed through a resistor, a voltage is dropped across the ends of the resistor. All resistors dissipate power when a voltage is applied. The power dissipated by the resistor is represented by P = V 2 R where P is the power dissipated (W), V is the voltage across the resistor (V), and R is the resistance (W). An ideal resistor dissipates electric energy without storing electric or magnetic 7 energy.

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9 Fixed Resistors: The fixed resistors are those whose value cannot be varied after manufacture. Fixed resistors are classified into composition resistors, wire-wound resistors, and metal-film resistors. Types: Wire Wound Resistor Carbon Resistor 9

10 Wire Wound Resistors: o Made by winding wire with a high resistivity of alloy like nickel-chromium, Copper alloys, Iron Chromium Aluminium alloys etc. on a ceramic/ plastic former tube. o After winding the wire is well protected from access of moisture to prevent electrolytic corrosion. o Resistance depends on the resistivity of the wire, the cross section and the length Materials of Wire wound resistor must have (i) high thermal stability (ii) good tensile strength (iii) capacity to withstand high temperature 10

11 Characteristics of wire wound resistors: Accurate resistances with low tolerances Withstand large power dissipation High accuracy Withstand mechanical shock and vibration Can carry large current Not suitable for high frequency Costly 11

12 Carbon Resistors o Carbon in amorphous form conducts current. o In Carbon resistors, finely ground carbon dust or graphite (conductor) is bound with a nonconducting ceramic powder (binder) o The ratio of carbon dust to ceramic (conductor to insulator) determines the overall resistance of the mixture - Higher the ratio of carbon, lower the overall resistance o Types: Carbon Composition Resistor (CCR) Carbon Film Resistor (CFR) 12

13 Carbon Composition Resistor (CCR) In this type, the carbon dust and the non-conducting ceramic powder mixture is moulded into a cylindrical shape with metal wires or leads attached to each end, then coated with an outer insulating material Colour coded markings are done to denote its resistance Characteristics of Carbon Composition Resistors: o Small in size o Wide range of resistance available o Cheapest o Good RF performance o High tolerance o Get heated up easily o Not useful above 5W power 13

14 Carbon Film Resistor (CFR) This type of resistor is constructed by depositing a film of carbon on to an insulating ceramic substrate of alumina The desired value of resistance is obtained (i) by trimming the layer of thickness or (ii) by cutting helical grooves of suitable pitch along its length. Characteristics: Wide ranges are available (<1Ω to many MΩ) Small in size Low in cost Can be used in high frequency Vulnerable to mechanical shocks Can not withstand high temperature Chemically reactive, so unstable 14

15 Variable Resistors: o A variable resistor is a device that is used to change the resistance according to our needs in an electronic circuit. o It can be used as a three terminal as well as a two terminal device. o Mostly they are used as a three terminal device. o Application: Change in resistance is required in a circuit Current to be controlled and regulated Voltage is varied, controlled or divided o Working of Variable Resistor a variable resistor consists of a track which provides the resistance path. Two terminals of the device are connected to both the ends of the track. The third terminal is connected to a wiper that decides the motion of the track. The motion of the wiper through the track helps in increasing and decreasing the resistance. o Type: i) Rheostat ii)potentiometer 15

16 Rheostat: o It is built with a resistance wire wound around a semicircular insulator or a heatresisting cylinder, with the wiper sliding from one turn of the wire to the next. o The rating of the rheostat is given with the full resistance value and the allowable power dissipation. o Applications: In DC motor drives, electric welding controls or in the controls for generators o Characteristics Can handle small and large power & voltage Large current carrying capacity Precision with low tolerances Costly and bulky o Applications: In high power circuits 16

17 Potentiometer: o Potentiometers comprise - a resistive element either carbon or wire wound - a sliding contact (wiper) that moves along the element - electrical terminals at each end of the element - a mechanism that moves the wiper from one end to the other and - a housing containing the element and wiper o Types of Potentiometer (i) Volume control type Has long shaft, Larger size (ii) Trimmer potentiometer No shaft, small in size 17

18 Volume Control Type Potentiometer Characteristics Cheaper Lesser in weight Range is from few hundreds of Ω to few MΩ o Applications Volume controls in radio, TV 18

19 Trimmer Potentiometer o Characteristics Miniature in size Low cost Range: Few Ω to few MΩ Need to use screw driver to rotate o Applications Calibration and balancing of electronic equipment Adjust bias in TV picture tube 19

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25 Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are: series parallel.

26 Series circuit : A circuit composed solely of components connected in series i.e. two elements are said to be in series whenever the same current physically flows through both of the elements. The current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component.

27 Parallel circuit : one connected completely in parallel i.e. Two elements are said to be in parallel when the same voltage physically appears across the two resistors. In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.