Types of Resistors and Selection Principles
1. Definition
2. Variety
3. Units
4. Power
5. Error
6. Identification method of resistance
7. Selection principle of resistance device
8. How Resistors work (Video)
1. Definition
Most of the resistor lead wires for the axial lead, a small portion of the radial lead, in order to adapt to the needs of modern surface mount technology (SMT), there are "no lead wires" chip resistor (or called footless parts), chip resistor chip resistor like the size of a grain of rice, flat, and generally use the automated placement machines. Placement. Resistors are non-polar components, the resistance value of the resistor can be identified in the component body through the color ring or engineering code.
2.Types
Different resistors not only have different resistance values, but also different functions, so different resistors are not interchangeable.
Resistor Selection - According to Resistor Type (more specific)
The following different types of circuits are mainly introduced: Chip Resistors, Plug-in Resistors, Wirewound Resistors, Current Sense Resistors, Thermistors, Potentiometers. Mainly from the characteristics, applications, packaging, and component selection.
A. Chip Resistors
Chip resistors have a size advantage over plug-in resistors and are well suited for printed circuit boards (PCBs).
Usage: Cement resistors are usually used for high power and high current applications with 2W, 3W, 5W, 10W or even larger power, like air conditioners, TV sets, and other electrical appliances with power above the hundred watt level, basically cement resistors are used.
Disadvantages: The disadvantages of cement resistors lie in the large size, the use of high heat, easy to disseminate, precision often can not meet the requirements of the use of stability and so on. Cement resistor shells are generally made of ceramic, whose main component is: Aluminum Oxide Al2O3, commonly known as corundum ceramic, which has the characteristics of fast heat dissipation and high strength.
Some common applications are pull-up/down, voltage divider, current limiting, and filtering signal bandpass filters at certain frequencies of high pass/low pass/. A 0Ω resistor can also be used as a jumper. There are two types of chip resistors: film resistors and thick film resistors.
1) Thin Film Resistors
Film resistors are used for applications such as high precision audio, medical or test equipment. Compared to thick film resistors, they have lower resistance variation (0.1%-2% accuracy), lower temperature coefficient (5 ppm/K) and less noise, but are more expensive.
2) Thick Film Resistors
Thick film resistors are the most common type of resistor and are required for most applications. Thick film resistors have high variations (1%-5% accuracy), higher temperature coefficients (50 ppm/K), and are noisier than thin film resistors. If there are no specific performance requirements, thick film resistors are usually preferred.
Packages: 0201, 0402, 0603, 0805, and 1206 are the most common.
The numbers represent imperial dimensions, 0402 is 0.04 X 0.02 inches, 0603 is 0.06 X 0.03 inches, and so on.
B, plug-in resistors
Plug-in resistors are popular and widely used, in particular. In circuit prototyping, easy to replace and can be used with the breadboard. The main functions are pull-up / pull-down, voltage divider, current limiting and filtering. There are several types of plug-in resistors.
Carbon film resistors and metal film resistors are the most popular among plug-in resistors.
1) Carbon Film Resistors
Carbon film resistors have a wide variation of resistance values (accuracy 2%-10%). E12 (± 10%), E24 (± 5%), and E48 (±2%) packages are most commonly used. Most applications have replaced carbon film resistors with metal film resistors. The temperature coefficient (TC) of carbon film resistors is usually negative - about -500ppm/K - but the exact value depends on the resistance value and size.
2) Metal Film Resistors
Metal film resistors have less variation in resistance value (accuracy 0.1%-2%) and higher stability.
Metal film resistors are most commonly available in E48 (±2%), E96 (±1 %) and E192 (±0.5%, ±0.25% and ±0.1%) packages. Because they offer better performance than carbon film resistors and are less expensive, metal film resistors have a temperature coefficient of resistance (TC) of approximately ±100 ppm/K - some parts have a positive TC while others have a negative TC.
Metal Film Resistor Construction Diagram
3) Carbon Component Resistors
Carbon composition resistors have been replaced by carbon or metal film resistors due to their high variability and poor stability. However, they have good high frequency characteristics and are good at withstanding high energy pulses, and are used in welding equipment and high voltage power supplies.
4) Metal Oxide Resistors
Metal Oxide was the first replacement for carbon composition resistors, but is being replaced by metal film resistors in most applications. They are still used in high durability applications as they can handle higher temperatures and have higher power ratings (>1W).
Typically the resistance value is determined by the color ring.
C. Wirewound Resistors
Wirewound resistors are made by winding thin wires around ceramic rods. They are used in high precision equipment such as multimeters, oscilloscopes and other measuring devices. Wirewound resistors that can pass high currents without overheating are used in power supplies and other high-current circuits.
Wirewound resistors can provide very high power ratings (up to 1000W) and can operate at very high temperatures (up to 300 degrees Celsius). They also have good long-term stability - 15-50 ppm/year variation compared to metal film resistors, which vary from 200-600 ppm/year - and are the best choice for noise performance.
Disadvantage: Only available in the low ohmic range (0.1Ω to 100kΩ). Because wirewound creates resistors, they have their own inductance, so they have the worst high frequency characteristics of all resistor types. They are also more expensive than other common types of resistors.
Applications: usually used in circuit breakers and fuses because of their high power capability.
D. Thermistor
Thermistors are resistors whose resistance changes significantly with temperature.
If you need to change resistance over a wide temperature range, use an NTC thermistor. the resistance of an NTC thermistor decreases with temperature, making it a good choice for temperature sensors between -55C and 200C. Use PTC thermistors when you need to change resistance suddenly at a specific temperature. PTC thermistors are popular for overcurrent protection applications. Holding current is the current when the PTC thermistor is absolutely "short-circuited", while trip current is the current when the PTC thermistor is absolutely "open-circuited".
E. Potentiometer
Potentiometers provide variable resistance and can be used for a variety of applications, such as amplifier gain control, circuit tuning, etc. Trimmer potentiometers (or trimmer pots) are small potentiometers that can be mounted on a PCB and adjusted with a screwdriver. They can be SMD or plug-in and can have top or side adjustment orientation. They can also be single-turn or multi-turn. Single-turn potentiometers are used in applications such as amplifiers where only a single control is required. Multi-turn potentiometers are used for more precise control and can have up to 25 turns.
3. Units
Resistors are measured in ohms (Ω), kilohms (KΩ), and megohms (MΩ).
Their conversion formula: 10^6Ω=10^3KΩ=1MΩ
4. Power
Power is measured in watts. The power of a resistor tells us how much energy it can release under normal use; the higher the power, the more energy it releases.
Note: Even though the resistors have the same resistance value, you should not use a low power resistor instead of a high power resistor.
5. Tolerance
Tolerance is the range of variation of the resistance value of a resistor, with a plus sign (+) or minus sign (-) to indicate the normal variation of its condition. For example, if a resistor has a resistance value of 100Ω±10%, the resistance value can vary between 90-110Ω.
Precision resistors with an error of ±2% or less are identified by five color rings: semi-precision resistors with an error of ±2% or more are identified by four color rings.
6. Resistor Identification Method
Color Ring Method
Scale Method
Direct marking method
7. Principle of resistor selection
Resistance value meets the requirements of the circuit
Allowable error within the design range of the circuit
Power to meet the circuit requirements
The volume meets the requirements of the circuit board used
8. How do Resistors work (Video)
Look at the following video.
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