eet 110 - electronics survey chapter 10 - resistors
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EET 110 - Electronics Survey
Chapter 10 - Resistors
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
Resistors
Ratings of resistors• RESISTANCE
– determined by markings
• TOLERANCE– determined by marking
• WATTAGE RATING– determined by size or marked
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.
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
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)
Resistor Color Code
consists of 4 bands of color1st & 2nd band give value3rd gives multiplier4th (if present) gives tolerance
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
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%
Color Code Mnemonic
Bugs Bunny Raids Our Young Garden, But Violets Grow Wildly
Black Brown Red, Orange, Yellow, Green, Blue, Violet, Gray, White
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
Size gives wattage1/8 watt
1/4 watt
1/2 watt
1 watt
2 watt
Series connection of resistors
Resistors connected in series result in added resistance
100 ohm
1000 ohms
500 ohm
Rtotal = 100 + 500 + 1000 ------ 1600 ohms
Series resistors
Voltage is distributed across the resistors
The voltage across each resistor in series is a proportion of the resistance to the total
Here each resistor is 1/3 of the total, so the 9 volts is distributed across the three resistors evenly - 3 volts each
1k
1k
1k
+9V
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
Parallel connection
In Parallel resistors, the INVERSE of the total is equal to the total of the inverses of each resistor in parallel.
150 150 150
1/Rt = 1/R1 + 1/R2 + 1/R3
1/Rt = 3/150 = 1/50
Rt = 50 ohms
To find the total resistance of two unequal resistors in parallel - use the formula
21
21
RR
xRRRT
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
Parallel Resistors
To find the total resistance of resistors in parallel
32
1111
1 RRR
RT
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
Two resistors in parallel, in series with a third
First solve for the parallel combination RT(parallel) = (30 x 60)/(30 + 60) = 20 ohms This leaves an equivalent
These two resistances in series gives RT = 40 + 20 = 60 ohms total
Homework
Do Problems – Ch9: 1&2, Ch10: 1-6Prepare for lab (ohm readings)Read Chapters 11 & 12