Electronic workshop Lecture3 Resistors Dr Imtiaz Hussain email

Electronic workshop Lecture-3 Resistors Dr. Imtiaz Hussain email: imtiaz. hussain@faculty. muet. edu. pk URL : http: //imtiazhussainkalwar. weebly. com/

Introduction •

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 0. 5 Watt 0. 25 Watt The size indicates the power rating, NOT the resistance value

4 -Band Resistors 1 st Band = 1 st Significant Digit 2 nd Band = 2 nd Significant Digit 3 rd Band = Multiplier 4 th 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 = 3 M. 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 1 k 100 k 1 M 10 M Tolerance [5] TC [6] 1% 2% 100 ppm 50 ppm 15 ppm 25 ppm 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: 1 st Band = 2 nd Band = 1 st Significant 2 nd Significant Digit 3 rd Band = 4 th Band = 3 rd Significant Multiplier Digit 5 th 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 10 2 % Resistor nominal value Tolerance = 2% = 100 101 = 1, 000 = 1 k.

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 (x 10) 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 4 th) 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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