Resistor is an electric component which resists the flow of electron. Resistor is a very basic and most common circuit element. We use resistor to control the current flow in an electric circuit. Controlling current is very important and electronic engineering is nothing but an art of controlling current. You can not find any electric device or circuit without resistor.
Resistors are passive components, meaning they only consume power (and can’t generate it). Resistors are usually added to circuits where they complement active components like op-amps, microcontrollers, and other integrated circuits. Commonly resistors are used to limit current, divide voltages, and pull-up I/O lines.
The electrical resistance of a resistor is measured in ohms. larger or smaller values of ohms can be matched with a prefix like kilo-, mega-, or giga-, to make large values easier to read. It’s very common to see resistors in the kilohm (kΩ) and megaohm (MΩ) range (much less common to see miliohm (mΩ) resistors). For example, a 4,700Ω resistor is equivalent to a 4.7kΩ resistor, and a 5,600,000Ω resistor can be written as 5,600kΩ or (more commonly as) 5.6MΩ.
The Different Types of Resistor
There are many thousands of different Types of Resistor and are produced in a variety of forms because their particular characteristics and accuracy suit certain areas of application, such as High Stability, High Voltage, High Current etc, or are used as general purpose resistors where their characteristics are less of a problem.
Some of the common characteristics associated with the humble resistor are; Temperature Coefficient, Voltage Coefficient, Noise, Frequency Response, Power as well as a resistors Temperature Rating, Physical Size and Reliability.
Based on the conductive properties of a resistor resistors can be classified as:
Linear Resistor: A linear resistor is the type of resistor whose resistance remains constant with increase in the potential difference or voltage applied to it. Or the Resistance or Current passed through the resistor does not changes as the applied voltage ( P.D ) changes. The V-I characteristics of such resistor is a straight line.
Non Linear Resistor: Non-Linear Resistor are those types of resistors in which the Current passed through it is not exactly directly proportional to the Potential Difference applied to it. These types of resistors have non-liner V-I characteristics and does not strictly follows ohm’s Law.
There are several types of nonlinear resistors, but the most commonly used include : NTC resistors (Negative Temperature Co-efficient) - their resistance lowers with temperature rise. PTC resistors (Positive Temperature Co-efficient) - their resistance increases with the temperature rise. LDR resistors (Light Dependent Resistors) - their resistance lowers with the increase in light. VDR resistors (Voltage dependent Resistors) - their resistance critically lowers as the voltage exceeds a certain value.
Non linear resistors are used in different projects. LDR is used as a sensor in various robotics an hobbyist project.
Based on Resistor’s Value
Fixed Value Resistor:
Fixed value resistors are those types of resistors whose value is fixed already while manufacturing and cannot be changed during it’s usage.
Variable Resistor or Potentiometer :
Variable Resistors or Potentiometers are those types of resistors whose Value can be changed during it’s usage. These types of resistor usually contains a shaft which can be rotated or moved by hand or a screw driver to change it’s value in between a fixed range for eg. 0 Kilo Ohms to 100 Kilo Ohms.
Potentiometers are used for volume and speed control in different projects and devices.
Package Resistor :
These types of resistor is a resistor which contains a package which contains two or more resistors inside it. It have many terminals and the resistor’s resistance can be chosen by using any two terminals among the available terminals or can also be used as an resistor array for various purposes.
Based On Composition :
Carbon Composition:
These types of resistors are made by a composition of Carbon Particles which are hold together by a binding resign. The proportion of carbon particles and resign used determines the value of the resistor. At both ends of the composition a Metal Cap with a small rod of tin is attached to solder it or use it in circuits , then the whole package is enclosed in a plastic case to prevent moisture and reaction with air.
These types of resistors normally produces noise in circuit due to electron passing through one carbon particle to another , thus these types or resistors are not used in critical circuits although they are cheap.
Carbon Deposition:
The resistor which is made by depositing a thin layer of carbon around a ceramic rod is called Carbon Deposition resistor. They are made by heating a ceramic rod inside a flask of methane and depositing the carbon around it by using Glass Cracking process. The value of resistor is determined by the amount of carbon deposited around the ceramic rod.
Metal Film:
Metal film resistors are made by depositing vaporized metal in vacuum on a ceramic core rod. these types of resistors are very reliable , have high tolerance and also have high temperature coefficient. These types of resistors are costlier compared to other but are used in critical systems.
Wire Wound:
Wire wound resistor are made by winding a metal wire around a ceramic core. The metal wire is an alloy of various metals based on the characteristics and resistance of the resistor required. These types of resistor have high stability and can also withstand high powers but are usually bulkier compared to other types of resistors.
Ceramic Metal:
These types of resistor are made by firing certain metals blended with ceramics on a ceramic substrate. The proportion of the mixture in the blended ceramic and metal determines the value of the resistor. These type of resistors are very stable and also have accurate resistance. These types of resistors are mostly used as Surface Mount type resistor for using in SMD PCB.
Based on Resistor’s Function:
Precision Resistors:
Precision Resistors are resistors that have very low tolerance values, so they are very precise (closely near
their nominal value).
All resistors come with a tolerance value, which is given as a percentage. The tolerance value tells us how close to the nominal value a resistance can vary. For example, a 500Ω resistor that has a tolerance value of 10%, may have a resistance that is somewhere between 10% above 500Ω (550Ω) or 10% below 500Ω (450Ω). If the same resistor has a tolerance of 1%, its resistance will only vary by 1%. Therefore, a 500Ω resistor can then vary between 495Ω and 505Ω. This is tolerance as an example.
A precision resistor is a resistor that has a tolerance level as low as 0.005%. This means a precision resistor will only vary 0.005% from its nominal value.
Precision resistors have very low tolerance percentage values, making them ultraprecise to their nominal values. They will vary very little from their nominal values, so they are used in applications where high-precision is necessary in terms of resistance values.
Fusible Resistor:
A Fusible Resistor is a wire-wound resistor that is designed to burn open easily when the power rating of the resistor is exceeded. In this way, a fusible resistor serves dual functions. When the power isn't exceeded, it serves as a resistor limiting current. When the power rating is exceeded, it functions as a fuse, burning up, and becoming an open in the circuit to protect components in the circuit from excess current.
Cement Resistors:
Cement resistors are power resistors that are heat and flame resistant. Cement resistors are made to handle a large amount of power flowing through it with it being undamaged by heat or flames. If you are designing a circuit where a lot of current is being passed through a resistor and with it needing to be resistant to high heat and flame, cement resistors is a good design choice.
Typical power ratings range from 1W to 20W or more. Tolerances from the stated resistance value are around 5 percent.
Thermistors:
A thermistor is a thermally sensitive resistor whose resistance value changes with changes in operating temperature. Because of the self-heating effect of current in a thermistor, the device changes resistance with changes in current.
Thermistors exhibit either a positive temperature coefficient (PTC) or a negative temperature coefficient (NTC). If a thermistor has a positive temperature coefficient, its resistance increases as the operating temperature increases. Conversely, if a thermistor has a negative temperature coefficient, its resistance decreases as the operating temperature increases.
How much the resistance changes with changes in the operating temperature depends on the size and construction of the thermistor. It's always best to check the datasheet of the thermistor in use to find out all the specifications of the thermistors.
Thermistors are frequently used in electronic circuits that handle temperature measurement, temperature control, and temperature compensation.
Photoresistors:
Photoresistors are resistors whose resistance values change according to the light striking the surface of the resistor. In a dark environment, the resistance of a photoresistor is very high, possibly several MΩ, depending on the resistance rating of the specific photoresistor in use. When intense light hits the surface, the resistance of the photoresistor drops dramatically, possibly to as low as 400Ω.
Thus, photoresistors are variable resistors whose resistance values change in regard to the amount of light hitting its surface.
Leaded and non-leaded resistor types
Leaded resistors: This type of resistor has been used since the very first electronic components have been in use. Typically components were connected to terminal posts of one form or another and leads from the resistor element were needed. As time progressed, printed circuit boards were used, and the leads were inserted through holes in the boards and typically soldered on the reverse side where the tracks were to be found.
Surface mount resistors:
These resistor types have been used increasingly since the introduction of surface mount technology. Typically this type of resistor is manufactured using thin film technology. A full range of values can be obtained.
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