1. Chapter 5: Resistors

2. 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 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

3. Resistors

4. 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

5. Surface Mount vs. Through Hole

6. Surface Mount Resistors (SMT)
Surface Mount Technology

7. Types of Fixed Resistors
Carbon Composition
Metal Film
Metal-Oxide Film
Resistor Networks
Wirewound Resistors
Old-skool
High accuracy
Low noise and good thermal properties
High accuracy at high resistance
Many packaged resistors
High power applications

8. Resistor Properties Value in Ohms Accuracy
Power rating (We’ll look at this one first)

9. What is Resistor Power Rating?
Examples:
¼ watt, ½ Watt, 20 watts
P = V·I = V2/R = I2R
Heat Sinks

10. Determining Value and Accuracy
Tolerance Color Code:
Brown = 1%
Red = 2%
Gold = 5%
Silver = 10%

11. Video See lecture notes first

12. More in class practice problems
Blue Blue Blue Gold
Brown Black Red Silver
Brown Black Orange Silver
Orange Violet Black Gold
66 MΩ +/- 3.3 MΩ = 62.7M to 69.3M
1000 Ω +/- 100 Ω = 900 to 1100
10000 Ω +/ Ω = to
37 Ω +/ Ω = to
Find tolerance range as well
… or you can just measure it with an Ohmmeter!

13. Reading Resistor Value on a Surface Mount Resistor
324
670
103
100
320,000 Ω
67 Ω
10k Ω
10 Ω
Potentiometers are written on the same way

14. What color is the following?
Green
Black
Violet
Blue

15. What color is the following?
Violet
Brown
Orange
Red

16. Homework Do problems 1 and 2 on page 85
Worksheet – Resistance and Voltage Worksheet
Include the range (if applicable)!

17. Other Calculator Functions
Talk about change button
Put Calculator in Write View (If doesn’t say w-view at top, go to Setup menu, press 2, press 0)
Talk about a/b button.
Moving left and right to correct mistakes.
Back space button
Using previous answer
Storing and recalling numbers
Changing from Degree to Radian in SET UP
x-1 button
Pi button
Sqrt button
Negative button
Using parenthesis a lot for parallel resistors
PEN vs DEC mode

18. Variable Resistors
Variable resistors are designed so that their resistance values can be changed
A potentiometer is a three terminal variable resistor used to divide voltage
A rheostat is a variable resistor used to control current

19. Pictures of Variable Resistors

20. Linear vs. Logarithmic “Pots”

21. Knob rotation (Usually 20 turns)
Linear vs. Logarithmic “Pots”
Knob rotation (Usually 20 turns)
See page 69 for schematic of application

22. 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.”

23. Resistors that change resistance with temperature
(Page 70 in book)
RTD’s (Need to be powered)
Bolometers - Thermistors (NTC) /Barreters (PTC)
Thermocouples (produces a voltage)
Negative vs. Positive Temperature coefficient.

24. Bad Resistors
Resistors can go bad when too much current is passed through them.
Signs of a resistor that has gone bad are:
Burned or charred looking
Smoky smell
Melted

25. Random Video of the Day