The most commonly used components in electrical circuits are resistors. These are used mainly for maintaining the specified values of voltage and current in an electrical circuit. The working principle of a resistor is based on Ohm’s law. According to the law, the voltage across the terminals of the resistor is directly proportional to the current flowing through it. Ohm is the unit of resistance. However, this article is a brief introduction to different types of resistors and how to calculate their colour codes.
Types of Resistors
The availability of resistors in the market is diverse, and they come in different shapes and sizes. A few of such different types of resistors are discussed below:
● Wire wound resistors
● Metal film resistors
● Variable resistors
● Thick film and thin film resistors
● Special resistors
Wire Wound Resistors
Wire-wound resistors are the oldest known resistor types that are famous for their high power ratings and low resistive values. They are made using alloys of either nickel-chromium or copper-nickel manganese alloy. They are similar to wires in appearance which makes them different from other resistor types.
Metal Film Resistors
Metal film resistors are known for reliability, accuracy, and stability over other resistors. They are available in different ranges such that they vary from few ohms to millions of ohms. They are made using either metal oxide or small rods of ceramic-coated metal. The resistivity of these resistors can be controlled by controlling the thickness of the coating layer.
The commonly known variable resistors are potentiometers and presets. The resistance of these resistors are fixed between the two terminals and are used for setting the sensitivity of the sensors and the voltage. Potentiometers, rheostats, and digital resistors are the different types of variable resistors.
Thick Film and Thin Film Resistors
In the making of thin-film resistors, resistive material is sputtered on an insulating substrate. The value of the resistive element that is used in the making of these resistors is close to 1000Å. Thin-film resistors have properties such as:
● Better temperature coefficients
● Less noise
● Parasitic inductance is low
● Lower capacitance
Thin-film resistors find applications in active and passive power components of microwave such as:
● In power terminations
● In power resistors
● In power attenuators
Thin-film resistors are most preferred because they have high accuracy and high stability.
While the thick film resistors are made using ceramics and powdered glass. Thick film resistors are available as low-cost resistors, and they have a tolerance between 1-2% and the temperature coefficient either between +200 or +250 and -200 and +250.
There are two special resistors and they are:
● Light-dependent resistors
A thermistor is a special resistor in which the resistance is dependent on the temperature. The term thermistor is a combination of thermal and resistor. For the preparation of thermistor, the oxides of metal are used that are either pressed into a bead or into a cylinder. Positive temperature coefficient and negative temperature coefficient are the two types of thermistors.
Light Dependent Resistors
Light-dependent resistors are mainly used in electrical circuits such as in street lights, clocks, and alarms. These resistors are available in different shapes and colours and are dependent on ambient light.
Colour Codes of Resistors
Now that we know that there are different types of resistors it becomes important to colour code these resistors. The easiest way to remember the resistor colour code is with the help of a mnemonic:
B B Roy of Great Britain has a Very Good Wife (BBRGBVGW).
The resistors are colour coded depending on the four, five, and six bands. To learn more about how to calculate the colour code of a given resistor, stay tuned.