Resistors_ types, colour coding

1. ELECTRONIC COMPONENTS

2. Electronic Components
Components
Passive Active
Vaccum tubes
Diodes
Transistors
Integrated circuits
Resistors
Capacitors
Inductors
Components are the basic building blocks of an electronic circuits.

3. Passive Components
• These components by themselves are not capable of amplifying or processing signals.
• They are linear elements which control or modify the output of electronic circuits without
playing an active role in its performance.
• Passive components either consume or store energy.
• But without the use of these components we cannot design and implement any electronic
circuit.
• eg: Resistors, Capacitors, Inductors

4. Passive Components

5. Resistors
 Passive components which provide an opposition to the charge-flow (or current) in a circuit.
This opposition is called resistance (R).
 measured in ohms (symbol is Ω).
 Resistors are the materials which opposes the flow of electric current.

6. • Resistance of any material,
𝑅 =
𝜌𝐿
𝐴
where ρ - specific resistance or resistivity, L - length, A – area of cross section
𝑅 ∝ 𝜌, 𝑅 ∝ 𝐿, 𝑅 ∝ 1/𝐴

7. Specifications of a resistor
• Resistance value
Value of a resistor expressed in ohms (Ω)
• Tolerance
Percentage deviation from the rated value
• Wattage rating or power rating
Maximum power that can be handled by the resistor safely, without damaging it (W)
Physical size of resistor gives an indication of its wattage rating
Common standard power ratings are ¼ W, ½ W,1W and 2W.

8. • Temperature coefficient of resistance, αT
Change in resistance with temperatue
If resistance increases with increase in temp- Positive temp - coeff. of resistance
Eg: Cu, Al, Tungsten
 If resistance increases with decrease in temp- Negative temp - coeff. of resistance
Eg: Semiconductors
Alloys like Magnanin, Constantan etc. shows zero temperatue coeff.of resistance
• Voltage coefficient of resistance, αv
Describes the change in resistance with voltage at a given temperature
• Voltage rating
Maximum voltage that can be applied across it, without causing damage to it.

9. Standard values of resistors
• When resistors are manufactured, certain preferred values are aimed at
• 20% tolerance series, 10% tolerance series, 5% tolerance series, 1% tolerance series
• For resistors other than preferred values, series and parallel combinations are used

10. Standard values of resistors

11. Colour coding of resistors
• Carbon resistors are colour coded to indicate their resistance values
• Standardized by Electronics Industries Association (EIA)
• Colour bands are read from left to right
Colour coding of resistors

12. Colour coding of resistors

13. Colour coding of resistors

14. Resistor types

15. FIXED RESISTORS:
• Resistors, whose ohmic values remain fixed at a constant value, are known as fixed resistors.
• Generally made of metals, highly conducting oxides and composite materials
• Semiconductors are not suitable as its resistivity changes with temperature
• Common types
Carbon composition resistors
Carbon/metal film resistors
Wire-wound resistors

16. 1. Carbon composition resistors
• These resistors do not need substrate since the stick itself is made of carbon
• They are made by mixing granules of carbon or graphite with a binding material (silica and
synthetic resin) to a doughy paste.
• Carbon content in the mixture determines the ohmic range and wattage

17. • These resistors are available in resistance values of 1Ω to 20 MΩ and power ratings of 1/10,
1/8 , ¼, ½, 1, 2 watts.
Advantages:
• Carbon-composition resistors are small in size compared with wire-wound resistors.
• A very wide resistance range is available.
• These are the cheapest resistors.
• These have good RF performance.

18. Disadvantages:
• Carbon-composition resistors have no precision, and have very high
tolerance.
• These resistors get easily heated and crack down on soldering.
• The resistance values of these resistors vary with aging.
• They are not useful for applications involving power levels above 5 watts.
Applications:
Carbon composition resistors are used for all general purpose circuits
including entertainment (Radio, T.V).

19. 2. Film Resistors
 Consists of a film of a resistive material having low temperature co- efficient of resistivity deposited
on a ceramic or glass substrate of rectangular or cylindrical geometry
 Materials used - carbon, tantalum, chromium and tin oxide
Depending on the thickness of the film we have thin film (< 5 μm) resistors and thick-film (> 5 μm)
resistors.
Carbon film resistor Metal film resistor

20. • Carbon film resistors are manufactured by depositing very thin film of carbon on to
a substrate of ceramic or glass tube.
• Groves are made on the carbon film to get the precise values
• Metal caps at the end serves as leads to resistor
• These resistors have power rating 1/8 W to 2W,
voltage ratings up to 1000V and are highly stable

21. Advantages:
• Available in wide range of resistor values, from very low values (< 1Ω) to many MΩ.
• Miniature size.
• Resistors commonly used in ICs.
• Used in high-voltage applications.
• Have good high-frequency properties.
• Low cost.

22. Disadvantages:
• Cannot withstand high temperatures.
• Cannot withstand mechanical shocks.
• Cannot withstand atmospheric moisture and humidity.
• Chemically reactive and hence unstable.
Applications:
These resistors are used in high frequency circuits and in circuits of computers, telephone
circuits and high fidelity amplifiers.

23. 3. WIRE WOUND RESISTORS
• They have low ohmic range and high wattage ratings
• Wires used should have low temperature coefficient of resistance, resistive against corrosion,
oxidation and linear expansion and should be mechanically strong
• Commonly used materials are Nichrome (80% Ni, 20% Cu), Constantan (60% Cu, 40% Ni)
and Manganin (84%Cu, 12%Mn, 4%Ni)
• Resistance value and power rating are determined by the gauge of wire and number of turns

24. • Wire wound resistors are constructed from a long fine wire (usually nickel-chromium wire)
that is wound on a ceramic core or epoxy moulded tubes (insulating core).
• The winding is done in a manner which minimize the inductive and capacitive effects at
high frequencies (beyond 200 kHz).
• Wire wound resistors are of two types
(i) power wire wound resistors
(ii) precision wire wound resistors.

25. • Power wire wound resistors are available in low (3, 5, 10 Watts), medium ( 10 to 60 W) and
high power (60-1000 W) types.
• Precision wire wound resistors are wound on ceramic tubes and sometimes on epoxy moulded
tubes.
• These precision wire wound resistors are available up to 5 W with ½ % and 1% tolerances and
are useful upto 5 to 10 MHz.

26. Advantages:
• Wire wound resistors can be designed to produce very accurate resistance values, with very low
tolerance (± 0.01%).
• They can with stand large power dissipation.
• They can be used in high-temperature situations.
• They are capable of carrying extremely large currents.
• Wire-wound resistors can with stand mechanical shock and vibration.
• They can be used in high-voltage circuits.
• Wire-wound resistors have very stable resistance values which do not change much with aging.

27. Disadvantages:
• Wire wound resistors are very large in size and weight.
• They are very costly.
• Power type wire wound resistors are not suitable beyond 200 kHz because of interwinding
inductance and the capacitance.
• In many situations, wires can break, leading to the breakdown of the circuit in which these
resistors are used.
Applications:
• Used in power supplies control circuits, as loads in television receivers.
• Precision type wire wound resistors are used in bridges, voltmeters and other instruments.

28. II. VARIABLE RESISTORS:
• Variable resistors are resistors whose resistance value can be varied between zero and certain
maximum value.
• In certain electrical/ electronic circuits sometimes it is necessary to change the values of
currents and voltages.
• For example it is often necessary to change the volume of sound and brightness in T.V, volume
of sound and tone in radios and to regulate the speed of a fan. Such adjustments can be done
by using variable resistors.

29. • Variable resistors can be
 General purpose type - can be wire-wound or carbon type
 Precision type - always wire-wound type
• Commonly used variable resistors are
Potentiometers
Rheostats

30. • Variable resistor is a three terminal component. There is a movable contact on the
resistive element.
• The position of the movable contact determines the resistance value in the circuit.
• The smaller variable resistors commonly used in electronic circuits are known as pots.

31. • Based on the material used for construction, potentiometers are classified into two types
1. Carbon potentiometers
2. Wire wound potentiometers

32. 1.1 Carbon Potentiometers
• A mixture of carbon, resin and clay are made on a plastic base and deposited on to a bakelite
substrate in the form of a segmented circle called an annular ring
• A sliding contact of beryllium copper alloy, moving over the annular ring provides the desired
resistance variation
• 3 lugs - 2 solder lugs form the end terminals and middle lug is connected to the variable arm
through a metal spring wiper
• As the shaft is rotated, the variable arm moves the wiper to make the contact at different points

33. • Its resistance range from 100Ω to 10MΩ.
Applications:
Used in electrical circuits and communication areas because of their low cost and high
frequency characteristics.
They are used in television for brightness and contrast control,in radio, for volume and
tone controls.
They are also used in various measuring instruments.

34. 1.2 Wire Wound Potentiometers
• For power rating of 3W or more and for uniform variation of resistance, wire-wound
potentiometers are used
• A laminated and insulated flat substrate is used as the former
• After winding the former with Nichrome wire, it is bent into a circular shape
• Former is housed in a polymer case, with a spindle which slides a wiper contact over the wire.
• Three terminals are provided – 2 fixed terminals and 1 variable terminal - The two outer terminals
are taken from the two ends of the wire and the middle terminal is taken from the rotating arm

35. • Resistance range from 0.1kΩ to 50kΩ and power rating is from 2W to 4W

36. • Wire wound potentiometer are of linear and non linear types.
• In the linear type, the former (the part over which resistance wire is wound) is of uniform height
and hence resistance varies linearly with the rotation of the contact.
• In a non-linear potentiometer the height of the former is not uniform and hence resistance
varies non linearly.
Applications
These are used in amplifiers, controlling motor speed, high stabilized circuits, analog
computers, radio receivers.

37. 2. Rheostats
• High power variable resistors are called rheostats
• Some have fixed trappings and some have sliding contact by which resistance can be varied
• Formed by winding suitable wire over a ceramic former coated with enamel
• The sliding contact can move along a line which gives linear variation in resistance
• Rheostats are available with power rating from 10 to 100W, with- standing temperature up to 300◦C
• Resistance value varies between 10Ω to 5kΩ