A Resistor And Different Types

A resistor is a two-terminal passive electronic component used in an electronic circuit that have a stated value of resistance. It is used to implement an electrical resistance in an electronic circuit. For the current to flow through a resistor, a potential difference is required between the two terminals of the resistor.

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The current through a resistor is proportional to the voltage across the resistance terminals. This relation is represented by the Ohm's law.

I = V/R

where I is the current through the terminals of the resistor, V is the voltage, and R is the resistance of the resistor. It can be also be cross multiplied to get the other values when 2 of the values are known. The unit of resistance is ohms. When the current flows through the resistor there will be resistance to the flow of current and as a result heat is dissipated from it.

There are a range of commercially manufactured resistors available in the market. The resistors comes with different resistance values as well as power or wattage rating. The electrical resistance value of the resistor is marked on it. The tolerance of the resistor along with the temperature coefficient is also written on it. Resistances of higher power rating are usually larger and bulky in size.

Resistances have characteristics such as series inductance and parallel capacitance, which may affect its performance in higher frequencies. The noise characteristics in the resistors is important in low noise electronic circuits such as RF amplifiers or preamplifier stages. The temperature coefficient of the resistance interfere with the resistance and the tolerance rate of the resistor.

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Types of Resistors

There are different types of resistors that are available in the market for using in electronic circuits. These resistors differ in the properties depending upon their manufacture and construction. Resistors are used in different applications with the frequency characteristics ranging from audio range of frequencies to ultra high frequencies.

Resistors are broadly classified into:

Fixed Resistors

These are the most commonly used resistors in electronic circuits. The value of the fixed resistor is a fixed one and cannot be changed in general. Their resistance is predetermined during the time of the manufacture and are available with a fixed value. The resistance values of the fixed resistors are marked using a color code, which is displayed as colored bars or colored stripes. The color coding for the resistors are used because the size of the resistor is very small for the resistance value to be written on it. The value of the resistor is a discrete value that is distinct from other values. There are 4 to 6 bands of colors marked on it for denoting its resistance values. The last band denotes the tolerance of the resistor which is the amount of the fixed value of the resistor that can vary during its use. The tolerance is calculated as a percentage value. Resistor values such as 1, 2.2, 4.7, 5.6, 10 etc. are usually seen. The different types of fixed value resistors are carbon film resistors, metal film resistors, and wire wound resistors.

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​Variable resistors

This is a resistor where the resistance of the resistor can be varied by changing the slider of the resistor. This consists of a main fixed resistor element and a slider, which taps on to the resistor. The value of the resistor can be varied to a suitable value by moving the slider control during the use. The slider control can be varied with the slider tap moving along the entire length of the resistor element. This consists of 3 connections, two of them are connected to both ends of the resistor element and one to the slider component. The connection can be taken between all these three connection positions or any one end of the resistor element and the slider. The rotation angle of a variable resistor is usually around 300 degrees. 
 

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There are 3 general types of variable resistors that are used.

1. Variable control resistor: The value of the resistor is changed or controlled during the operation of a circuit. Eg. Volume control of a radio. When the control is moved or turned around, the value of the resistor is changed and the volume or whatever is adjusted.

2. Semifixed resistors: The value of the resistor is changed by a slider and fixed to that position for the best performance of the circuit. Semifixed resistors are used to compensate for the inaccuracies of the resistor. It is also used to fine tune the performance of the circuit. These are also called as preset resistors. The value of the resistor is not meant to be adjusted by the user but instead by a technician. It is used to adjust the operating condition of the circuit by the technician.

3. Potentiometers: The value of these resistors are varied by turning the control of the resistor many times to use the whole range of the resistor. This allows for very precise adjustment of the resistor value. These are also called as multiturn potentiometers, trimmer potentiometers, or trimpots. Eg. Resistor tuning in a radio circuit or fine adjustments in a circuit.