RESISTORS ACCORDING TO COMPOSITION
O B J E C T I V E S • Identify the types of resistors. • Discuss the importance of each resistor. • Differentiate each according to usage and composition.
RESISTORS One of themostcommonelectroniccomponentsused as a devicethatlimits, orresistscurrent and produces a desiredamount of voltage in thecircuitisthe resistor. It can bemadefromdifferentmaterials, butthemostcommonisthecarboncomposition. Thecurrentlimitingability, orresistance can bevariedbychangingthe ratio of carbontobindingagent.
ACCORDING TO COMPOSITION • CarbonCompositionResistors • Standard Film Resistors • Chip Resistors • Network Resistors • Wire-WoundResistors • Potentiometers • Rheostats
CARBON COMPOSITION CCRs are madeeitherbyhotorcoldmoldingfrom mixtures of carbon and claybinder. These has become a dominantdiscrete resistor mainlyforitslow-costreliabilty in general purposeapplications and foritsresistivetolerances of ±5% to ±20%.
Itsresistivevaluerangesfrom 10 ohmstomegaohms, in power ratings from 1/8 to 4 watts . It has abilitytowithstandhighercurrent surges and ruggedness. Itisusednotonlyforcommercialbutalsoformilitary and aerospaceapplications.
STANDARD FILM A circular resistor withtwopinsextendingfromoppositesidesorthebarrel-shapedresistors.
CHIP RESISTOR Thistype of resistor wasintroduced in the late 80´s toaccomodatefortheevershrinkingcomputercomponentswherethere can be up to 6 layers per circuitboard.
NETWORK RESISTOR Thistype of resistor comes in compact form and can contain up to 12 resistors in a compact space.
WIRE- WOUND RESISTORS Thistype of resistor has a highlyresistivewireswrappedaroundaninsulatingcore. Insulatingcores are usuallymade of cementorceramicmaterialsorjustplainpaperorpressedcardboard.
Sincebarewires are usedfordesiredresistance, theunitisencasedbyaninsulating material. Thistype of resistor provideslowresistancewithhighwattagesrangingfrom 5 to 100 wattsor more. They are bestchoice in applicationswhereaccurate and stableresitances are necessary.
These are resistors in whichtheresistiveelementis a length of highresistancewireorribbonusuaalynichromewoundontoaninsulatingform.
POTENTIOMETER These are manufactured in a widerangestartingfrom 1 wattto 5000 watts. Thesemaybe open type, perforatedtype, and gradedtype. Thestandardtoleranceis ±10% butclosertolerance can bealsosupplied.
RHEOSTATS The most common way to vary the resistance in a circuit is to use a rheostat.The word "rheostat" was coined about 1845 by Sir Charles Wheatstone, from the Greek word rheos meaning stream, and stat meaning regulating device, which is a two-terminal variable resistor. For low-power applications (less than about 1 watt) a three-terminal potentiometer is often used, with one terminal unconnected or connected to the wiper.
QUIZ NO. 2 RESISTORS