Transcript Chapter 5: Resistors - Mt. San Antonio College

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 zigzag 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
Old-skool

Metal Film
High accuracy

Metal-Oxide Film
Low noise and good thermal properties
High accuracy at high resistance

Resistor Networks
Many packaged resistors

Wirewound Resistors
High power applications
Surface Mount Technology
Surface Mount Resistors (SMT)
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
o_tF0

More in class practice problems
Blue Blue Blue Gold
66 MΩ +/- 3.3 MΩ
Brown Black Red Silver
1000 Ω +/- 100 Ω
Brown Black Orange Silver
10000 Ω +/- 1000 Ω
Orange Violet Black Gold
37 Ω +/- 1.85 Ω
Find tolerance range as well
… or you can just measure it with an Ohmmeter!
Reading Resistor Value on a
Surface Mount Resistor
324
320,000 Ω
670
67 Ω
103
10k Ω
100
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”
Linear vs. Logarithmic “Pots”
Knob rotation (Usually 20 turns)
See page 69 for schematic of application
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.
“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.”
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