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Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2002 The McGraw-Hill Companies Grob Schultz

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Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2003 The McGraw-Hill Companies 2 CHAPTER Resistors

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Topics Covered in Chapter 2 Types of Resistors Color Codes Variable Resistors Rheostats and Potentiometers Power Rating Series and Parallel Combinations Resistor Troubles

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Types of Resistors Wire-wound resistors Carbon-composition resistors Film-type resistors Surface-mount resistors Fusible resistors

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Wire Wound Resistor 12, 10 Watt

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1/2 Watt 1/4 Watt Carbon Composition Resistors

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Metal Film Resistor 1 Watt

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Chip Resistors (also called surface-mount)

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1 k SIP Resistor (Single In-line Package) 12345 6 7 8

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0 Black 1 Brown 2 Red 3 Orange 4 Y ellow 5 Green 6 Blue 7 Violet 8 Gray 9 White Color Code Resistor Color Code 1 st digit 2 nd digit multiplier tolerance

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Yellow = 4 Violet = 7 Red = 2 Gold = 5% 4700 5% of 4700 = 235 4700 + 235 = 4935 4700 - 235 = 4465 is the nominal value. The actual value can range from 4465 to 4935. Applying the Color Code

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Whats the nominal value and range? 1 k (950 to 1050 ) 390 (370.5 to 409.5 ) 22 k (20.9 to 23.1 k ) 1 M (950 k to 1.05 M )

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Resistors Under 10 The multiplier band is either gold or silver. For gold, multiply by 0.1. For silver, multiply by 0.01. 56 5.6 0.56 10

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Five-Band Code The first three stripes are digits. The fourth stripe is the multiplier. The tolerance is given by the fifth stripe: Brown = 1% Red = 2 % Green = 0.5% Blue = 0.25% Violet = 0.1% 1.58 k

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Zero-Ohm Resistor No resistance Used for connecting together two points on a printed-circuit board Body has a single black band around it Wattage ratings are typically 1/8 or 1/4-Watt

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Rheostats and Potentiometers Rheostat Two terminals Connected in series with the load and the voltage source Varies the current Potentiometer Three terminals Ends connected across the voltage source Taps off part of the voltage

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Wiping contact Fixed contact Rheostats are two-terminal devices. Wiper arm

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Using a Rheostat to Control Current Flow

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Panel mount type Circuit board type (trimmer) Potentiometers 8 V10 V 6 V 4 V

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Power Rating of Resistors A larger physical size indicates a higher power rating. Higher-wattage resistors can operate at higher temperatures. Wire-wound resistors are physically larger and have higher power ratings than carbon resistors.

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Series and Parallel Combinations of Resistors Series Combination Higher resistance Higher power rating Parallel Combination Lower resistance Higher power rating

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Series-Parallel Combinations Series-Parallel combination Higher resistance Higher power rating

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Resistor troubles include open devices and devices that are out of tolerance (usually on the high end). An open resistor shows an infinite resistance. 1 k nominal 1.5 k An example of an out-of-tolerance resistor

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One obvious clue that all experienced technicians have seen is a resistor that is burnt black. This is usually caused by a short circuit which causes high current to flow in the resistor. When a resistors power rating is exceeded, it can burn up.

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