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

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Introduction

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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

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

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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.

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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.

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Resistors Surface Mount Resistors or SMD Resistors

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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

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Variable Resistors

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Reading Resistor Values Color Code Numerical Code

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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 5 band Resistor 6 band Resistor

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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.

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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

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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 ____ %

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How do we know which color corresponds to which number? NameColorValue Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 White 9

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

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

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5-Band Resistors ColorDigits [1-3]Multiplier [4]Tolerance [5]TC [6] Black01 Brown1101%100ppm Red21002%50ppm Orange31k 15ppm Yellow410k 25ppm Green5100k0.5% Blue61M0.25% Violet710M Gray8 White9 Gold 5% Silver 10%

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

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

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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%.

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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 1 0.5 50

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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 To download this lecture visit http://imtiazhussainkalwar.weebly.com/

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