Transcript Lecture-3 - Dr. Imtiaz Hussain

Electronic workshop
Lecture-3
Resistors
Dr. Imtiaz Hussain
email: [email protected]
URL :http://imtiazhussainkalwar.weebly.com/
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
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
Carbon Resistors
• One type of fixed resistor is the composition carbon
resistor.
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.
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.
Resistors
• Surface Mount Resistors or SMD Resistors
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
Variable Resistors
Variable Resistors
Reading Resistor Values
• Color Code
• Numerical Code
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
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.
Resistor with Different Power Ratings
Examples:
2 Watts
1 Watt
1 Watt
0.5 Watt
0.25 Watt
0.25 Watt
The size indicates the power rating, NOT the resistance value
4-Band Resistors
1st Band =
1st Significant Digit
2nd Band =
2nd Significant Digit
3rd Band =
Multiplier
4th Band =
Tolerance
___ ___  10    ____ %
How do we know which color corresponds to
which number?
Name
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Color
Value
0
1
2
3
4
5
6
7
8
9
Determine the nominal resistance value and the tolerance for the resistor shown
below.
Brown =1
Black =0
Red =2
Gold = 5%
2

1
0
5 %
___ ___  10
  ____
Nominal value
= 10102
= 1,000
Tolerance = 5%.
Determine the nominal value and tolerance for the resistor below.
Orange =3
Black =0
3 ___
0  10
___
Green =5
5

Silver = 10%
  ____
10 %
Resistor nominal value = 30105
= 3,000,000
= 3M.
Tolerance = 10%
5-Band Resistors
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
Silver
Digits [1-3]
0
1
2
3
4
5
6
7
8
9
Multiplier [4]
1
10
100
1k
10k
100k
1M
10M
Tolerance [5]
TC [6]
1%
2%
100ppm
50ppm
15ppm
25ppm
0.5%
0.25%
5%
10%
5-Band Resistors
• For resistors with 1% or 2% tolerance, the color code consists of 5 bands.

The template for 5-band resistors is:
1st Band =
2nd Band =
1st Significant 2nd Significant
Digit
Digit
3rd Band =
4th Band =
3rd Significant Multiplier
Digit
5th Band =
Tolerance
___ ___ ___  10    ____ %
Determine the nominal resistance and tolerance for the resistor shown below.
Brown = 1
Black =0
Black = 0
Brown = 1
Red =  2%
1
1 ___
0 ___
0  10 
2 %
___
  ____
Resistor nominal value
Tolerance = 2%
= 100101
= 1,000
= 1k.
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%.
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.
1
1  10    ____
2 ___
3
0.5 % ___
50 ppm/K
___
___
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.
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END OF LECTURE-3