Published : 2020-05-07 ¿Como elegir una resistencia? - Categories : , Products What Is A Resistor? A resistor is an electrical component that is designed to limit or regulate the flow of electrical current in an electronic circuit. Resistors are passive in nature and are also employed to get the desired specific voltage for an active device such as a transistor. Types Of Resistors Resistors are distinguished on various grounds such as its construction, power dissipation capacities, the material used and tolerance to various external parameters. To understand this better, let us classify resistors in two types: 1. Fixed Resistor A resistor having a fixed, defined electrical resistance which is not adjustable is known as a fixed resistor. 2. Variable Resistor or Adjustable Resistor As the name suggests variable resistors are the ones in which the value of resistance can be adjusted. Variable resistors are further divided into 'potentiometers', 'rheostats' and 'trimpots'. 3. Resistors which are determined by physical quantity ● Thermistors (NTC and PTC) ● Photo Resistors (LDR) ● Varistor (VDR) ● Magneto Resistor (MDR) Further, we can understand the types of resistors on the basis of material and manufacturing process used in its making. 1. Carbon Composition Resistor (CCR) The resistive element of a CCR resistor is made from a mixture of fine carbon particles and a non-conductive ceramic material. 2. Carbon Film Resistor This type of resistor is made by depositing a thin and pure carbon film on an insulating cylindrical core. 3. Metal Film Resistor A metal film resistor is made of the alloy 'nichrome'. However, other materials such as tantalum nitride are also used in its making. 4. Metal Oxide Film Resistor This type of resistor is nearly similar to a Metal Film resistor except that the resistive material in a Metal Oxide Film resistor is made of a metal oxide such as tin oxide. 5. Wire Wound Resistor (WWC) Wirewound resistors are made by winding a wire of magnesium or constantan around a non-conductive core. An insulating material is used to cover the resistive wire. 6. Foil Resistor A foil resistor is made of an alloy of nickel, chromium, and additives are used to construct the foil. It is then placed on top of a ceramic carrier which offers high heat conductivity. The graphic symbol used to represent a resistor is: How Does A Resistor Work? Let us understand the working of a resistor by the way of comparing its functioning with an analogous mechanical principle. For this, we shall take the classic 'drinking a smoothing' example. Here, your ease of drinking the smoothie is determined by the diameter of the straw. Smaller the diameter, the harder it will be to draw the smoothie and vice versa. The size of the medium (straw) , therefore, determines the unease (resistance) created during the passage (of smoothie). A resistor is responsible for performing exactly the same function in electronic circuits. It resists the flow of electrical current when a voltage is applied across it. The amount of resistance created by the resistor is called the 'resistance'. The value of resistance is quantified with the units of Ohms. Ohm's Law Ohm’s law is the basic rule of electricity which explains the relationship between electric current, voltage, and resistance. According to Ohm's law, when a voltage of V is applied across the terminals of a resistor, the current allowed by the resistor is simply calculated with the following formula: U = V / R Here, Current is denoted by U. It is determined in units of 'amperes' Voltage is denoted by V. It is determined in the units of 'volts' Resistance is denoted by R. Resistance is determined in the units of 'ohms' The figure below shows a simple electrical circuit with a resistor working on the principle of Ohm's law. How To Connect A Resistor? Resistor is one electrical component that is employed in a host of applications. Almost all circuits and electronic devices come fitted with it. Upon looking at an electric circuit, you will find several resistors working together in a connection. Resistors are connected mainly in two ways: Series Connection Parallel Connection How To Measure Resistance? Electrical resistance is measured by either of the two: Constant Current Method or Constant Voltage Method. In the constant current technique, a known level of current is passed through an unknown level of resistance. The voltage which occurs as a result of this action is taken as the value of electrical resistance. For measurement of resistance via the constant voltage technique, a known level of voltage is sourced across an unknown resistance and the resultant current is measured. Further, measurements can also be performed using the indirect method. In this, current flows through a resistor leading to a drop in the level of voltage. This drop is used to determine the measurement of resistance. Characteristics Of A Resistor When it comes to resistors, there are several factors to consider. The performance of a resistor is not only determined by its resistance but by a host of several other parameters as well. Take a look at a few of these parameters: ● Temperature Coefficient The value of a resistor is determined by the length, cross sectional area and resistivity of the resistive material from which it is made. ● Frequency Response This parameter comes into significance particularly when you are dealing with an AC circuit. The changes in the levels of frequency is dealt with a built-in property known as 'reactance'. ● Power Dissipation Power dissipation is referred to as the measure of the amount of power that a resistor can dissipate without overheating. ● Maximum Voltage The fluctuations in voltage has an impact (electrical stress) on the materials from which the resistor is made. If this voltage exceeds the maximum capacity of the resistor, uttar will lead to a sudden breakdown of the resistor. ● Maximum Temperature Resistors can function efficiently only within a specified range of temperature. If the temperature is well within the specified range, parameters such as tolerance and temperature coefficient, it will continue to work well. However, any excess in the temperature beyond its given range can lead to malfunctioning. How To Choose A Resistor For Your Project? To begin with, you need to determine the resistance value using the Ohm's law. Second, ascertain the amount of power that the resistor needs to dissipate. Power dissipation in a resistor can be calculated with the following formula: P=I*V Please note that it is preferable to use a resistor which has twice the power rating than you require. For example, if your project needs a power rating of 140mW, then choose a 250 mW resistor. Employing this mechanism helps in dealing with fluctuations. Further, you have to consider several other parameters that influence the quality and efficiency of the resistor. In order to be more agile in checking whether the resistor fits your project check the below table of colors used to denote resistors Final Thoughts It is well said that size does not determine the worth of something. Resistors are the best example of this. From the smallest of electrical equipment to the largest of supercomputers, a resistor has a great role in making all of them run smoothly.