Different Types of Resistors
- Resistors ( R ), are the most fundamental and commonly used of all the electronic components. There are many different Types of Resistors available to the electronics constructor, from very small surface mount chip resistors up to large wire wound power resistors.
- Mainly (Fixed and Variable)
Fixed Resistor
In an electrical circuit, some objects may need a
lesser amount of current than the input value. In such cases, fixed resistors
are used to reduce the flow of current. The
value of the resistance is fixed and does not change with change in the applied
voltage or current flowing through it.
The resistance value is measured in ohms and the
value ranges from a few milliohms to about a giga-ohm.
Fixed value resistors can be classified into
four broad groups:
- Carbon
Composition Resistor - Made of
carbon dust or graphite paste, low wattage values
- Film or
Cermet Resistor - Made from
conductive metal oxide paste, very low wattage values
- Wire-wound
Resistor - Metallic
bodies for heatsink mounting, very high wattage ratings
- Semiconductor
Resistor - High
frequency/precision surface mount thin film technology
Applications:
Resistors are universally used in all electrical
circuits of devices like TVs, radios, refrigerators, machines,
microelectronic semiconductor devices, regulators, etc.
a.)
Composition
Type Resistors
·
Carbon Resistors are the most common type of Composition Resistors. Carbon
resistors are a cheap general purpose resistor used in electrical and
electronic circuits.
·
Their
resistive element is manufactured from a mixture of finely ground carbon dust
or graphite (similar to pencil lead) and a non-conducting ceramic (clay) powder
to bind it all together.
b.) Film Type Resistors
·
The
generic term "Film Resistor" consist of Metal Film, Carbon
Film and Metal Oxide Film resistor types, which are generally
made by depositing pure metals, such as nickel, or an oxide film, such as
tin-oxide, onto an insulating ceramic rod or substrate.
·
The
resistive value of the resistor is controlled by increasing the desired
thickness of the deposited film giving them the names of either
"thick-film resistors" or "thin-film resistors".
·
Metal Film Resistors have much better temperature stability than their carbon equivalents,
lower noise and are generally better for high frequency or radio frequency
applications.
·
Metal
Oxide Resistors have
better high surge current capability with a much higher temperature rating than
the equivalent metal film resistors.
c.)
Cermet Resistors
·
Another
type of film resistor commonly known as a Thick Film Resistor is
manufactured by depositing a much thicker conductive paste of CERamic
and METal, called Cermet, onto an alumina ceramic substrate.
·
Cermet
resistors have similar properties to metal film resistors and are generally
used for making small surface mount chip type resistors, multi-resistor
networks in one package for pcb's and high frequency resistors. They have good
temperature stability, low noise, and good voltage ratings but low surge
current properties.
d.)
Wire
wound Type Resistors
·
Another
type of resistor, called a Wirewound Resistor, is made by winding a thin
metal alloy wire (Nichrome) or similar wire onto an insulating ceramic former
in the form of a spiral helix similar to the film resistor above.
·
These types of resistors are generally only available in very low ohmic
high precision values (from 0.01 to 100kΩ)
due to the gauge of the wire and number of turns possible on the former making
them ideal for use in measuring circuits and Whetstone bridge type
applications.
·
Power
Wire wound Resistor
are high temperature, high power and non-inductive resistor types generally
coated with a vitreous or glass epoxy enamel for use in resistance banks or DC
motor/servo control and dynamic braking applications. They can even be used as
space or cabinet heaters.
Variable Resistance
- A variable resistor is a potentiometer with only two connecting wires instead of three. However, although the actual component is the same, it does a very different job.
- The pot allows us to control the potential passed through a circuit. The variable resistance lets us adjust the resistance between two points in a circuit.
- For circuits requiring a resistance that can be adjusted while it remains connected in the circuit ( E.g: volume control on radio), variable resistors are required. They usually have 3 lead two fixed and one movable
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