Resistor is the passive circuit linear element which opposes the flow of current or electricity.
As the name indicate linear element it means that as the voltage applied to the resister is changes(increase/decrease),the current flowing through this resister is also changes.
So the relation between the voltage, current and resistance is given by
I=V/R (Ohms Law)
Resistance is a property of a material which changes according to the resistivity of the material.
The relation between the length, area and resistivity is given by
R = ρ ℓ / A
Power rating is a maximumpower which is handled by the resistor.
Mathematically it is written as
Power rating ranges from 1/16W to 300W.
While selecting the resistor apart from power rating the ambient temperature is also consider.
Tolerance is a deviation in the resistance from the normal value.
Tolerance ranges from 0.1% to 20%.
As the temperature changes the amount of resistance is changes this amount of resistance is nothing but the Temperature Coefficient.
Resistor is not purely resistive in nature it has some inductance and capacitance due to that maximum frequency at which this resistor can be operated is limited.
This parameter is also consider while selecting a resistor for high frequency application.
Stability is the fix, unchanged or constant resistance value over the period of time.
Every resistor has its own noise, while selecting the resistor for low noise application this parameter are consider.
Resistors are divided into two types namely Fixed and Variable.
The fixed resistor is again divided into the six types namely Carbon Composite Resistor, Carbon Film Resistor, Metal Film Resistor, Metal Oxide Film Resistor, Wire Wound Resistor and Surface Mount Resistor.
In fix resistor the value of the resistor is can’t vary once the fabrication is done while in variable resistor the value of the resistor is vary by varying the knob.
The carbon composite resistor is made up of carbon particles and binder like a clay.
This type of resistor are used in high energy pulses application.
Due to the poor stability, poor coefficient , more noise, less accurate Carbon Composite Resistor are replaced by the Film type of resistor.
Carbon film resistor contain ceramic substrate and thin layer of carbon film has been deposited in the form of a helix.
According to the pitch of the helix the resistance value of this resistor is changed.
It has low cost, low noise, low tolerance used in high voltage and high temperature application.
Metal film resistor is same as carbon film resistor only change is that carbon film is replace by metal film. Metal film has been deposited on a ceramic substrate.
It has low cost, low noise, good stability.It is used for high frequency application.
Metal oxide film resistor is quite similar to the metal film and carbon film resistors only difference is that metal and carbon film is replace by metal oxide film which is deposited on the ceramic substrate and tin oxide is used as a metal oxide layer.
It is used in high temperature and high surge applications.
In wire wound resistor the metallic resistive wire is wound around the ceramic material.
Thickness and gaugeof metallic wire defines the resistance value of this resistor.
Copper alloy and silver alloy are used for resistive wire.
It has high accuracy, low temperature coefficient used in high power and high precision application. But it is not suitable for high frequency applications.
In surface mount resistor metal film or metal oxide film is used as resistive element.
On top of the resistive film a thin layer of insulating layer has been deposited, metallic contact is present on both the side of this resistor so that this resistor is soldered on the PCB.
It has very high accuracy and very low tolerance value.
In variable resistor by changing the knob the value of the resistor will be changed.