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EET 110 - Electronics Survey

EET 110 - Electronics Survey. Chapter 10 - Resistors. Resistors. Resistor Wire Nichrome wire used for heating - I 2 R high resistance results in a voltage drop Resistors made from a variety of materials The lead pencil resistor. Resistors. Ratings of resistors RESISTANCE

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EET 110 - Electronics Survey

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  1. EET 110 - Electronics Survey Chapter 10 - Resistors

  2. Resistors • Resistor Wire • Nichrome wire used for heating - I2 R • high resistance results in a voltage drop • Resistors • made from a variety of materials • The lead pencil resistor

  3. Resistors • Ratings of resistors • RESISTANCE • determined by markings • TOLERANCE • determined by marking • WATTAGE RATING • determined by size or marked

  4. Types of resistors • Wire-wound resistors • usually larger, power resistors • Carbon Composition resistors • a cylindrical shaped block a carbon compound • Film type resistors • a layer of resistive material on an insulated rod • Both Carbon Composition and film type resistors are embedded in a cylindrical package.

  5. Types of resistors • Resistor networks • a number of resistors packaged together as group of identical resistors. • Precision resistors • usually +/- 1% • Adjustable resistors • changeable after the circuit is constructed - trimmer or variable types

  6. Rheostats & Potentiometers • Potentiometers • a POT • variable resistor with three terminals • each end of a resistive path and a wiper • Rotary or slide pot • Trimmer • screw variable • Taper • may be linear or non-linear (logarithmic)

  7. Resistor Color Code • consists of 4 bands of color • 1st & 2nd band give value • 3rd gives multiplier • 4th (if present) gives tolerance

  8. Resistor Color Code • Black 0 1 • Brown 1 10 • Red 2 100 • Orange 3 1000 • Yellow 4 10000 • Green 5 100000 • Blue 6 1000000 • Violet 7 10000000 • Gray 8 • White 9

  9. Resistance is read by taking the color code • And applying the color code • here RED = 2, VIOLET = 7, BROWN = x10 • gives 270 ohms • GOLD = +/- 5%

  10. Color Code Mnemonic • Bugs Bunny Raids Our Young Garden, But Violets Grow Wildly • Black Brown Red, Orange, Yellow, Green, Blue, Violet, Gray, White

  11. Precision Resistors • 1 % and 2% tolerance resistors must have THREE significant digits of value • Brown, Black, Black, Black, Brown • 100 x 1 w/ Brown = +/- 1% tolerance

  12. Size gives wattage 1/8 watt 1/4 watt 1/2 watt 1 watt 2 watt

  13. Series connection of resistors • Resistors connected in series result in added resistance 100 ohm Rtotal = 100 + 500 + 1000 ------ 1600 ohms 500 ohm 1000 ohms

  14. Series resistors • Voltage is distributed across the resistors

  15. The voltage across each resistor in series is a proportion of the resistance to the total 1k Here each resistor is 1/3 of the total, so the 9 volts is distributed across the three resistors evenly - 3 volts each +9V 1k 1k

  16. Series Resistors • Resistors in Series have an equivalent total resistance equal to the algebraic sum of each resistance. • The voltage across any one resistor is series is given by the ‘Voltage Divider Rule’ VT = R i/RT x VT (page 108) • see example 10-2

  17. Parallel connection • In Parallel resistors, the INVERSE of the total is equal to the total of the inverses of each resistor in parallel. 1/Rt = 1/R1 + 1/R2 + 1/R3 1/Rt = 3/150 = 1/50 Rt = 50 ohms 150 150 150

  18. To find the total resistance of two unequal resistors in parallel - use the formula

  19. For example if a 60 ohm and 40 ohm resistor are connected in parallel, the total resistance is given as RT = (60 x 40)/(60 + 40) = 2400/100 = 24 ohms

  20. Parallel Resistors • To find the total resistance of resistors in parallel

  21. Series - Parallel Connection • If combinations of resistors are connected in series and parallel, a total can be derived, by alternately simplifying with the series / parallel formulas • See example 10-7

  22. Two resistors in parallel, in series with a third

  23. First solve for the parallel combination • RT(parallel) = (30 x 60)/(30 + 60) = 20 ohms • This leaves an equivalent

  24. These two resistances in series gives • RT = 40 + 20 = 60 ohms total

  25. Homework • Do Problems – Ch9: 1&2, Ch10: 1-6 • Prepare for lab (ohm readings) • Read Chapters 11 & 12

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