“RESISTORS”

DEFINITION - It is an electronic component that has the ability to resist and/or oppose the flow of free electrons (current).

Resistors Range Value Value - From less than 1Ω up to 20MΩ Size Size - Vary from microscopic up to too large to carry

Two categories: 1. Fixed resistors 2. Variable resistors

Fixed Resistors Have single value of resistance Have single value of resistance Three Characteristics: 1. Value 2. Power rating 3. Tolerance

VALUE Indicates the nominal or ideal amount of resistance

POWER RATING This indicates the amount of power that can be dissipated for an indefinite amount of time without degrading the performance of the resistor This indicates the amount of power that can be dissipated for an indefinite amount of time without degrading the performance of the resistor Depends on the physical size of the resistor Depends on the physical size of the resistor

RESISTOR TOLERANCE The allowable variation which is expressed as a percent Common resistor tolerance: 1%, 2%, 5%, 10%, & 20%

Four major classes: 1. Carbon Composition 2. Film 3. Wirewound 4. Surface-Mount Technology (SMT)

CARBON COMPOSITION RESISTOR Use a mixture of carbon and an insulating filler as the resistive element; this mixture is pressed into a cylindrical form and coated with hard nonconductive material.

FILM RESISTORS Made by depositing a thin layer of resistive material onto an insulating tube or rod called the substrate. Use high-speed industrial laser for trimming, as for the laser etches away portions of the deposited film, the higher the resistance is known as the process known as spiraling.

DIFFERENT TYPES OF MATERIALS USED FOR FILM RESISTOR: 1. Carbon (Carbon Film) 2. Nickel – Chromium (Metal Film) 3. Metal & Glass (Metal Glaze Film) 4. Metal & Oxide Mixture (Metal Oxide)

WIREWOUND RESISTORS - Are made by winding resistive wire around an insulating rod. Value of a particular wirewound resistor can be determined by the ff.: Value of a particular wirewound resistor can be determined by the ff.: 1. Type of wire 2. Diameter of the wire 3. Length of the wire used to wind the resistor

Appearance of wirewound resistors Construction of wirewound resistor

SURFACE – MOUNT RESISTOR - Have no leads, their contacts solder directly to pads on the printed circuit board (PCB). It is commonly used when small size is an important consideration.

RESISTOR COLOR CODE

VARIABLE RESISTORS The resistance of a variable resistor can be adjusted by turning a knob or a rotating screw.

2 Major types: 1. Rheostat - Is a two (2) terminal device whose resistance can be change. 2. Potentiometer - Is a three (3) terminal device that is constructed much like a rheostat.