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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 the most common electronic components used as a device that limits, or resists current and produces a desired amount of voltage in the circuit is the resistor. It can be made from different materials, but the most common is the carbon composition. The current limiting ability, or resistance can be varied by changing the ratio of carbon to binding agent.

ACCORDING TO COMPOSITION Carbon Composition Resistors Standard Film Resistors Chip Resistors Network Resistors Wire-Wound Resistors Potentiometers Rheostats

CARBON COMPOSITION CCRs are made either by hot or cold molding from mixtures of carbon and clay binder. These has become a dominant discrete resistor mainly for its low-cost reliabilty in general purpose applications and for its resistive tolerances of ±5% to ±20%.

Its resistive value ranges from 10 ohms to megaohms, in power ratings from 1/8 to 4 watts . It has ability to withstand higher current surges and ruggedness. It is used not only for commercial but also for military and aerospace applications.

STANDARD FILM A circular resistor with two pins extending from opposite sides or the barrel-shaped resistors.

CHIP RESISTOR This type of resistor was introduced in the late 80´s to accomodate for the ever shrinking computer components where there can be up to 6 layers per circuit board.

NETWORK RESISTOR This type of resistor comes in compact form and can contain up to 12 resistors in a compact space.

WIRE- WOUND RESISTORS This type of resistor has a highly resistive wires wrapped around an insulating core. Insulating cores are usually made of cement or ceramic materials or just plain paper or pressed cardboard.

Since bare wires are used for desired resistance, the unit is encased by an insulating material. This type of resistor provides low resistance with high wattages ranging from 5 to 100 watts or more. They are best choice in applications where accurate and stable resitances are necessary.

These are resistors in which the resistive element is a length of high resistance wire or ribbon usuaaly nichrome wound onto an insulating form.

POTENTIOMETER These are manufactured in a wide range starting from 1 watt to 5000 watts. These may be open type, perforated type, and graded type. The standard tolerance is ±10% but closer tolerance can be also supplied.

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.

Any potentiometer may be connected as a rheostat. RHEOSTATS

QUIZ NO. 2 RESISTORS