1. Electronic workshop
Lecture-3
Resistors

2. Introduction A material that opposes the flow of electric current
Resistance is measured in ohms (𝛀)
Resistors are "Passive Devices", that is they contain no source of power or amplification but only attenuate or reduce the voltage or current signal passing through them.
Resistors can be either fixed or variable in value
𝑉=𝐼𝑅

3. Resistor

4. Fixed Resistors
Fixed resistors have only one Ohmic value, which cannot be changed or adjusted.
Fixed resistors come in a variety of different shapes, sizes and forms
Fixed resistors are made of
Carbon composition
Metal films
High-resistance wire

5. Carbon Resistors
One type of fixed resistor is the composition carbon resistor.

6. Metal Film Resistors
Metal film resistors are another type of fixed resistor. These resistors are superior to carbon resistors because their ohmic value does not change with age and they have improved tolerance.

7. Resistors
Wire-wound resistors are fixed resistors that are made by winding a piece of resistive wire around a ceramic core. These are used when a high power rating is required.

8. Resistors
Surface Mount Resistors or SMD Resistors

9. Variable Resistors Variable resistors can have two or three terminals.
Variable resistors are classified as a rheostat or a potentiometer.
Rheostat: Two- terminal device
Potentiometer: Three-terminal device

10. Variable Resistors

11. Variable Resistor
Resistive material is deposited on a non-conducting base.
stationary contacts are connected to each end of the resistive material.
Finally, a moving contact or wiper is constructed to
move along the resistive material and tap off the
desired resistance.

12. Variable Resistors

13. Variable Resistor

14. Reading Resistor Values
Color Code
Numerical Code

15. Resistor Color Code
Manufacturers typically use a color band system known as the resistor color code.
The resistor color code can be used to determine the resistor’s ohmic value and tolerance.
4 band Resistor
6 band Resistor
5 band Resistor

16. Resistor Color Code
The power rating is not indicated in the resistor color code and must be determined by experience using the physical size of the resistor as a guide.
For resistors with 5% or 10% tolerance, the color code consists of 4 color bands.
For resistors with 1% or 2% tolerance, the color code consists of 5 or 6 bands.

17. Resistor with Different Power Ratings
Examples:
2 Watts
1 Watt
0.5 Watt
0.25 Watt
The size indicates the power rating, NOT the resistance value

18. 4-Band Resistors ___ ___  10    ____ % 1st Band =
1st Significant Digit
2nd Band =
2nd Significant Digit
3rd Band =
Multiplier
4th Band =
Tolerance
___ ___  10    ____ %

19. How do we know which color corresponds to which number?
Name
Color
Value
Black
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Grey 8
White 9

20. Determine the nominal resistance value and the tolerance for the resistor shown below.1
Brown =1
Black =0 2
Red =2 5
Gold = 5%
___ ___  10    ____ %
Nominal value = 10102
= 1,000
Tolerance = 5%.

21. Resistor minimum & maximum value
Minimum and maximum resistance can be calculated using the tolerance value:
Minimum Resistance: 1000− 1000𝑥 Ω
(1000−50)Ω
950Ω
Maximum Resistance: 𝑥 Ω
( )Ω
1050Ω

22. Determine the nominal value and tolerance for the resistor below.
Silver = 10% 10
Orange =3 3
Black =0
Green =5 5
___ ___  10    ____ %
Resistor nominal value = 30105
= 3,000,000
= 3M.
Tolerance = 10%

23. 5-Band Resistors Color Digits [1-3] Multiplier [4] Tolerance [5]
TC [6]
Black 1
Brown 10 1%
100ppm
Red 2
100 2%
50ppm
Orange 3 1k
15ppm
Yellow 4
10k
25ppm
Green 5
100k
0.5%
Blue 6 1M
0.25%
Violet 7
10M
Gray 8
White 9
Gold 5%
Silver
10%

24. 5-Band Resistors ___ ___ ___  10    ____ %
For resistors with 1% or 2% tolerance, the color code consists of 5 bands.
The template for 5-band resistors is:
1st Band =
1st Significant
Digit
2nd Band =
2nd Significant
3rd Band =
3rd Significant
4th Band =
Multiplier
5th Band =
Tolerance
___ ___ ___  10    ____ %

25. Determine the nominal resistance and tolerance for the resistor shown below.
Brown = 1 1
Black =0
Black = 0
Brown = 1 1
Red =  2% 2
___ ___ ___  10    ____ %
Resistor nominal value = 100101
= 1,000
= 1k.
Tolerance = 2%

26. 6-Band Resistors
The template for 6-band resistors is:
Resistors with 6 bands are usually for high precision resistors that have an additional band to specify the temperature coefficient (ppm/K).
The most common color for the sixth band is brown (100 ppm/K).
This means that for a temperature change of 10 ˚C, the resistance value can change 0.1%.

27. 6-Band Resistors Orange (3) Red (2) Brown (1) Brown (x10) Green (1%)
Red(50 ppm/K)
3.21 k Ω 0.5% 50 ppm/K.
___ ___ ___  10    ____ % ___ ppm/K 3 2 1
0.5 50

28. SMD Resistor Coding
The first two (or 3) digits are the first two (or 3) digits of the resistance in ohms, and the third(or 4th) is the number of zeros to follow - the 'multiplier'.
Resistances of less than 10 ohms have a 'R' to indicate the position of the decimal point.

30. Activity; Light intensity control using potentiometer (variable resistor)
Connect the following circuit Rotate the spindle of potentiometer and observe the variation in darkness or brightness of bulb.

31. End of Lecture-3