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 step up or lower the voltage at different points in a circuitResistors work as they turn voltage energy into heat2 Functions:To limit currentTo produce desired voltageAnalogy
6 Types of Fixed Resistors Carbon CompostionMetal FilmMetal-Oxide FilmResistor NetworksWirewound ResistorsOld-skoolHigh accuracyLow noise and good thermal propertiesHigh accuracy at high resistanceMany packaged resistorsHigh power applications
7 Surface Mount Resistors (SMT) Surface Mount Technology
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 wattsP = V*I = V2/RHeat Sinks
10 Determining Value and Accuracy Tolerance Color Code:Brown = 1%Red = 2%Gold = 5%Silver = 10%
12 More in class practice problems Blue Blue Blue Gold66 MΩ +/- 3.3 MΩBrown Black Red Silver1000 Ω +/- 100 ΩBrown Black Orange Silver10000 Ω +/ ΩOrange Violet Black Gold37 Ω +/ ΩFind tolerance range as well… or you can just measure it with an Ohmmeter!
13 Reading Resistor Value on a Surface Mount Resistor 324320,000 Ω67067 Ω10310k Ω10010 Ω
14 Homework Do problems 1 and 2 on page 85 Include the range (if applicable)!
18 Knob rotation (Usually 20 turns) Linear vs. Logarithmic “Pots”Knob rotation (Usually 20 turns)See page 69 for schematic of application
19 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 equationTherefore 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.”