chapter 5: resistors. what is a resistor? definition: a device used in electrical circuits to...

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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