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The word “resistance” often gets a bad rap. It is commonly associated with unruly children, the inability to change, and political upheaval. Even Star Trek jumped on the bandwagon when their galactic bad-guys the Borg coined the phrase; “resistance is futile.” But resistance can serve a lot of good purposes too. We all want a strong immunity to resist the common cold, and those people who live downstream of a dam are thankful for its ability to resist the water that would otherwise flood their homes. Another important application of resistance is in electronic circuitry.
Electronic circuits are dependent upon resistor components to reduce or control current flow. Resistors can be fixed to provide a specific value of resistance, or variable to adjust circuit levels such as dimming a light. Resistors come in uncountable variations of physical sizes and shapes to accommodate their different uses. They are categorized by their value of resistance measured in ohms, as well as their range of tolerance to their value and how much power they can handle in watts. Let’s take a look at what some of the types of resistors and their applications are to get a better idea of what they do.
To understand what a resistor is and what it does, we need to go back to the basics of Ohm’s Law. Here we see that there are three key attributes of an electrical circuit; voltage, current, and resistance. To provide the resistance attribute, materials that restrict the flow of electricity are packaged in the components that we call resistors.
If you need to create 2 amps of current in a 12 volt system for your circuit, you would use the formula of volts divided by current to find the value of resistance needed. In this case it would be V / I = R, or 12 volts divided by 2 amps meaning that you need 6 ohms of resistance. This is an extremely simple example, but it demonstrates how the performance of every circuit is a product of the interaction of voltage, current, and resistance.
In a complex set of circuits as on a circuit board, there will be resistors doing different functions. Fixed resistors will be used to create correct voltage and current levels, adjust signal levels, and terminate transmissions lines. Variable resistors will be used for circuit adjustments, while larger resistors will be used in power circuits. In some cases resistors will be used to pull a logic signal up to a voltage level or down to a ground level to keep it from floating in an unknown state so that it can be correctly interpreted by the microcontroller.
Some resistor symbols that could be used on a schematic
There are a lot of variations of resistors for different functions. There are fixed resistors, variable resistors, trimmer resistors, thermistors, and photoresistors to name a few. Most of these resistors are two pin components, although some like variable resistors or resistor networks will have more. Resistors are typically represented on a schematic by a symbol with two solid horizontal lines representing its pins and diagonal lines in the middle as shown in the picture above. On a schematic this symbol can be rotated 90 degrees if necessary. This resistor symbol can also have a rectangle instead of the diagonal lines.
Variations of this symbol could include diagonal or vertical arrows representing additional pins of a variable resistor, or contained within a circle for thermistors and photoresistors. Multiple resistor symbols replicated within a larger rectangle is used for a resistor network. No matter how it is depicted, the symbol must clearly show that its electrical function is a resistor. The symbol also needs to display identification text along with it including its reference designator, value, and tolerance.
Different components including resistors in this 3D layout 3D screenshot
On the layout side of the PCB design tools, the goal is to model the physical shape of a resistor as clearly as possible into CAD parts called footprints. Precise footprints are important in order to show how many leads the resistor has, where they will solder onto the board, and the contours of the part outline. 3D data is also important to give the user the full depth of the resistor when laying out the circuit board.
There are a lot of types of different resistor footprints required for layout, and they can be broken into the following categories:
Thru-Hole Resistors: The resistor is a small cylindrical part with leads on either end which are bent over to be inserted and soldered into holes in the circuit board. These resistors come in different lengths, widths, and heights. The more power that a resistor is rated for, the larger it may be and it may be box shaped instead of cylindrical. Thru-hole resistors usually have bands of different colors painted on them to signify their values and tolerances.
Surface Mount Resistors: These same resistors can also be found in surface mount packages that get soldered flat onto metal pads on the circuit board. SMT resistors can be much smaller than their thru-hole counterparts which makes them more desirable for densely placed PCBs. SMT resistors have their values and tolerances stamped on them in text.
Variable and other Shapes of Resistors: Resistor footprints can vary a lot for the other types of resistors such as variable resistors, thermistors, etc. Some of these resistors will have three leads instead of two, while some may be taller than they are wide. In the case of a resistor network, multiple resistors are bundled together in one package that will share one common pin.
Printed Resistors: Resistor material can also be printed directly onto the circuit board negating the need for soldering physical resistors on the board. This saves space but often these resistors don’t have the precision that a packaged resistor will have.
You will be working with a lot of resistors as you design circuit boards, and the PCB design systems from Cadence have the features and functionality you need to help you choose and create the right resistor symbols and footprints. With its symbol and shape creation abilities, OrCAD PCB Designer is the PCB design tool you need to get the job done right.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
In your daily life, you use many electronic appliances. Maximum appliances used at home consist of an electric component known as a resistor. These resistors are mostly used in heaters, light bulbs, microwaves, electric stoves, toasters, and other heating appliances. In an electronic circuit, the flow of the current or limits of current is done by a resistor. To provide a particular voltage range for an active device, resistors are used as transistors.
Resistors are classified into two types. These types of resistors are further divided into subcategories. The types of resistors are as follows:
The current in the linear resistor will be directly proportional to the voltage applied to the resistor. The resultant graph of the linear resistor will be between the current (I) and voltage (V). The linear resistor graph will have a straight I-V curve.
Linear resistors are further divided into two types:
Fixed resistors have specific values, and these specific values cannot be changed. These fixed resistors are used for the appliance which never needs to change their value.
Variable resistors have values that can be varied or changed, and these variable values can be changed using a dial, screw, button, or knob. These variable resistors are used for appliances like radios with knobs, lights with switches, and television.
The current in the non-linear resistor will be indirectly proportional to the voltage applied to the resistor. Current In the resistor changes with the exchange in the temperature or voltage exchange. Values of non-linear resistors aren’t changed according to Ohm’s law. The resultant graph of the non-linear resistor will be between the current (I) and voltage (V). The non-linear resistor graph will have a non-linear I-V curve.
Non-linear resistors are further divided into three types:
Thermistors resistors are a kind of variable resistors. Thermistors identify the temperature change. These thermistor resistors have two terminals, and it is sensitive to temperature. The resistance value of the thermistor resistor is inversely proportional to the temperature.
A non-linear varistor resistor is made of semiconductors. The current through the varistor depends non-linearly on the voltage applied across the resistor. The most commonly used form for the varistor resistor is MOV or metal oxide varistor.
Photo resistors are also called LDR (light-dependent resistors). The other names of the photo resistors are photoconductive cells and light-controlled variable resistors. The photoresistor’s resistance decreases with an increase in the intensity of the incident light. So, the photoresistor’s resistance is inversely proportional to the intensity of the incident light.
The fixed and variable resistors are types of resistors called linear resistors. These fixed and variable resistors are further classified into sub-categories.
There are seven types of resistor, including the fixed resistor, which are as follows:
A form of a passive component is called a wire-wound resistor. A wire wound resistor is created by wrapping metal wire around a metal core. The metal wire serves as the electric current’s resistive component. Thus, the metal wire restricts a specific level of electric current. As a non-conductive substance, the metal core is placed. As a result, it blocks the flow of electric current.
The most precise and reliable parts to employ to limit the flow of electric current to a specific level are foil resistors. Compared to other types of resistors, foil resistors generate little noise. The TCR (Temperature Coefficient of Resistance) of foil resistors is low.
A passive component that limits the flow of electric current to a set level is a resistor made of carbon called a carbon composition resistor. The cylindrical resistive element used to create the carbon composition resistors has integrated metal end caps. The ceramic and carbon powder combination is used to create the cylindrical resistive element of the carbon composition resistor. The carbon powder effectively conducts electric current.
The carbon film resistor is the most common type of resistor used in electrical circuits. The carbon film is applied to a ceramic substrate to create the carbon film resistors. The ceramic substrate serves as an electrical current insulator, while the carbon sheet functions as a resistive element to the current.
A form of a passive component known as a metal film resistor uses metal film to limit the flow of electric current to a specific level. In contrast to metal film resistors, which use chromium, nickel, tin, and antimony to create their films, carbon is used to create the film in carbon film resistors. The TCR (temperature coefficient of resistance) of metal film resistors is low.
The metal glaze resistor is a passive component used to limit the flow of electric current to a certain level by combining glass powder with metal particles. Low TCR (temperature coefficient of resistance) for metal glaze resistors.
A form of a passive component known as a metal oxide film resistor uses metal oxide film as the resistive element to limit the flow of electric current to a specific level. Metal oxide film resistor construction is virtually identical to metal film resistors.
There are seven types of the resistor of variable resistor, which are as follows:
Three terminals make up the potentiometer, two fixed and one movable. The track’s two resistive ends are linked to the potentiometer’s two fixed terminals, while the third terminal is connected to the slider or sliding wiper. The current flow in the potentiometer decreases when the resistance of the potentiometer is increased.
Humistor name is the combination of humidity and resistor. Humidity affects humistors quite strongly. Resistive humidity sensors and humidity-sensitive resistors are other names for humidistats.
Rheostats are built in a manner that is virtually identical to potentiometers. However, we utilize two terminals of a rheostat to act. The length of the resistive element or track through which the electric current flows determines the rheostat’s resistance.
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Resistance of Thermistors depends on the surrounding temperature change. Positive temperature coefficient (PTC) and negative temperature coefficient (NTC) thermistors are the two types of thermometers. While PTC thermistors experience an increase in resistance as the temperature rises, NTC thermistors experience a reduction in resistance as the temperature rises.
The resistance of the magneto resistor varies when a magnetic field is supplied to the magneto resistor. Similarly, the magneto resistor’s resistance dropped as the magnetic field’s strength increased.
The word photoresistor is the combination of the terms photon and resistor. The photoresistor experiences a change in resistance when light energy is applied. As the applied light intensity rises, the photo resistor’s resistance falls.
As the name indicates, the force-sensitive resistors are extremely sensitive to the applied force. Force sensors, pressure sensors, force-sensing resistors, or FSR are other names for force-sensitive resistors.
Things to Consider When Using Various Types of Resistors
Power dissipation and temperature coefficients are the two factors to be mindful of when using a type of resistor.
Power Dissipation: Power dissipation is an important consideration when selecting a resistor. Always select a resistor with a lower power rating than the current being passed through it. So, choose a resistor with a power rating at least twice as high.
Temperature Coefficients: The most important thing to remember when working with resistors is that they must be used at high temperatures or else the resistance will flow dramatically. The temperature coefficient of a resistor is classified as either negative or positive (PTC).
The value of the resistor isn’t displayed outside. Through the color pattern, the resistance of the resistor can be calculated. The (PTH) plated-through-hole resistors use the color coding system; these colors add flair to the circuit when connected. In the case of (SMD) surface mount device resistors, they have their value marking system.
The color codes of the resistors are as follows:
ColorColor codeBlack
0
Brown
1
Red
2
Orange
3
Yellow
4
Green
5
Blue
6
Violet
7
Gray
8
White
9
The value of the resistor of the deviation from the nominal value is known as the tolerance of resistors. This value is expressed with the ±% symbol. The resistor’s tolerance is used to identify the resistor, giving a more accurate resistance reading.
Tolerance of the resistor according to the color:
ColorToleranceBrown
±1%
Red
±2 %
Gold
±5%
Silver
±10%
Wire applications wrapped resistors kind of include shunt with ampere meters which essentially used for accurate measurement, high sensitivity very balanced current regulation in a generally major way.
Photo resistors are used in various products, including photography equipment, burglar alarms, and flame detectors in a pretty big way.
Voltmeter and temperature control generally is controlled by resistors, contrary to popular belief.
Amplifiers, telephony, oscillators, and digital multimeters all need resistors, which is particularly significant. They are also utilized in transmitters, demodulators, and modulators, which are particularly fairly significant.
Resistors are part of appliances used in daily life. These resistors are used in circuits. Practical work with resistors will help to know the usage and working of the resistor in the circuit. In physics, resistors are to know the behavior of different resistors, i.e., the flow of the current, voltage flow, etc.
There are many different types of resistors. Each type of resistor is used in different circuits according to their behavior. To know which type of resistor should be used in the circuit, the color of the type of resistor table should be referred to.
A. There are many types of resistors. The main classification of resistors is two types that are linear and nonlinear. These are further divided into subcategories. The linear resistors are divided into fixed and variable resistors. The nonlinear resistors are divided into a thermistor, photoresistor, varistor, and surface mount resistor.
A. Flameproof wire wound resistors are used in the chargers as chargers are the input devices. The limited current should supply from the charger as a wire wound resistor is created by wrapping metal wire around a metal core. The metal wire serves as the electric current’s resistive component. Thus, the metal wire restricts a specific level of electric current. As a non-conductive substance, the metal core is placed. As a result, it blocks the flow of electric current. So the chargers will be working without any high voltages.
Ans. The type of resistor used in a bulb is tungsten. The filament in the bulb doesn’t have a specific resistance level, so when the voltage through the bulb has increased, the current is also increased. The increase in current results in the temperature of the bulb. As a result, the bulb glows.
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