chapter 5: resistors. what is a resistor? definition: a device used in electrical circuits to...
TRANSCRIPT
Chapter 5: Resistors
What is a resistor?
Definition: A device used in electrical circuits to maintain a constant relation between current flow and voltage. Resistors are used to step up or lower the voltage at different points in a circuit
Resistors work as they turn voltage energy into heat
2 Functions: To limit current To produce desired voltage
Analogy
Resistors
Resistor’s Schematic Symbol
Composed of a zig-zag line
What is the value of the resistor on the right?
Reference Designators
300 Ω 30kΩ
Surface Mount vs. Through Hole
Surface Mount Through Hole
Types of Fixed Resistors
Carbon Compostion
Metal Film
Metal-Oxide Film
Resistor Networks
Wirewound Resistors
Old-skool
Low noise and good thermal properties
Many packaged resistors
High accuracy at high resistance
High power applications
High accuracy
Surface Mount Resistors (SMT)Surface Mount Technology
Resistor Properties
Value in Ohms Accuracy Power rating (We’ll look at this one first)
What is Resistor Power Rating?
Examples:¼ watt, ½ Watt, 20 watts
P = V*I = V2/R Heat Sinks
Determining Value and Accuracy
Tolerance Color Code:
Brown = 1%
Red = 2%
Gold = 5%
Silver = 10%
Video
See lecture notes first http://www.youtube.com/watch?v=kvQBhX
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More in class practice problems
Blue Blue Blue Gold
Brown Black Red Silver
Brown Black Orange Silver
Orange Violet Black Gold
Find tolerance range as well
… or you can just measure it with an Ohmmeter!
66 MΩ +/- 3.3 MΩ
1000 Ω +/- 100 Ω
10000 Ω +/- 1000 Ω
37 Ω +/- 1.85 Ω
Reading Resistor Value on a Surface Mount Resistor
324
670
103
100
320,000 Ω
67 Ω
10k Ω
10 Ω
Homework
Do problems 1 and 2 on page 85
Include the range (if applicable)!
Variable Resistors
Pictures of Variable Resistors
Linear vs. Logarithmic “Pots”
Knob rotation (Usually 20 turns)
See page 69 for schematic of application
Linear vs. Logarithmic “Pots”
“The larger the cross-sectional area of the conductor, the more electrons are available to carry the current, so the lower the resistance. The longer the conductor, the more scattering events occur in each electron's path through the material, so the higher the resistance. Different materials also affect the resistance.”
Resistance of a Wire•The longer a wire is, the more resistive it is.•The thicker a wire is, the less resistive it is. (Think parallel)
•(Also think of a fire hose. There is always pressure drops across a pipe, but less pressure drop for bigger hoses.)
•Resistance is given by the following equation
•Therefore as a wire gets longer, the resistance change gets linearly larger.
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