Classification by volt-ampere characteristics
For most conductors, at a certain temperature, the resistance remains almost unchanged and has a certain value, and this type of resistance is called a linear resistance. The resistance of some materials varies significantly with current (or voltage), and its volt-ampere characteristic is a curve. This type of resistance is called nonlinear resistance. Under the action of a given voltage (or current), the ratio of the voltage to the current is the static resistance at the operating point, and the slope on the volt-ampere characteristic curve is the dynamic resistance. The way to express nonlinear resistance characteristics is more complicated, but these nonlinear relationships have been widely used in electronic circuits.
Sort by material
a. Wire-wound resistors are made of high-resistance alloy wires wound on an insulating skeleton, and are coated with a heat-resistant glaze insulating layer or insulating varnish. Wirewound resistors have a low temperature coefficient, high resistance accuracy, good stability, heat resistance and corrosion resistance, and are mainly used as precision high-power resistors. The disadvantage is that the high frequency performance is poor and the time constant is large.
b. Carbon synthetic resistors are made of carbon and synthetic plastics.
c. Carbon film resistors are made by coating a layer of carbon on the ceramic tube, and depositing crystalline carbon on the ceramic rod skeleton. Carbon film resistors have low cost, stable performance, wide resistance range, low temperature coefficient and voltage coefficient, and are currently the most widely used resistors.
d. The metal film resistor is formed by coating a layer of metal on the ceramic tube, and the alloy material is evaporated on the surface of the ceramic rod skeleton by vacuum evaporation.
Metal film resistors have higher precision, better stability, lower noise and lower temperature coefficient than carbon film resistors. It is widely used in instrumentation and communication equipment.
e. The metal oxide film resistor is made of a layer of tin oxide plated on the porcelain tube, and a layer of metal oxide is deposited on the insulating rod. Since it is an oxide itself, it is stable at high temperature, thermal shock resistance, and strong load capacity. According to the application, there are general, precision, high frequency, high voltage, high resistance, high power and resistance network.
special resistor
1. Fuse resistor: also known as fuse resistor, it plays the dual role of resistance and fuse under normal circumstances. When the circuit fails and its power exceeds the rated power, it will fuse like a fuse to disconnect the connection circuit. The fuse resistance generally has a small resistance value (0.33Ω ~ 10KΩ), and the power is also small. Common types of fuse resistors are: RF10 type, RF111-5 symbol type of fuse resistor, RRD0910 type, RRD0911 type, etc.
2. Sensitive resistor: It means that its resistance value is sensitive to certain physical quantities (such as temperature, humidity, light, voltage, mechanical force, and gas concentration, etc.). When these physical quantities change, the resistance value of the sensitive resistor will change. It will change with the change of physical quantity, showing different resistance values. According to the sensitivity to different physical quantities, sensitive resistors can be divided into thermal sensitive, humidity sensitive, photosensitive, pressure sensitive, force sensitive, magnetic sensitive and gas sensitive and other types of sensitive resistors. The materials used in sensitive resistors are almost all semiconductor materials, and such resistors are also called semiconductor resistors.
The resistance of the thermistor varies with temperature, and the resistance is a negative temperature coefficient (NTC) thermistor when the temperature rises. The most widely used is the negative temperature coefficient thermistor, which can be divided into ordinary type negative temperature coefficient thermistor; voltage regulator type negative temperature coefficient thermistor; temperature measurement type negative temperature coefficient thermistor and so on. A photoresistor is a resistor whose resistance changes with the intensity of incident light.
When the incident light increases, the photoresistor decreases, and when the incident light decreases, the resistance value increases.
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