For most conductors, the resistance remains almost constant at a certain temperature and is a certain value. This kind of resistance is called linear resistance. The resistance of some materials obviously changes with the current (or voltage), and its V-A characteristic is a curve. This kind of resistance is called nonlinear resistance. Under the action of a given voltage (or current), the ratio of voltage to current is the static resistance at the working point, and the slope on the V-A characteristic curve is the dynamic resistance. The expression of nonlinear resistance characteristics is complex, but these nonlinear relations have been widely used in electronic circuits.
Classification by material
- The wire wound resistor is formed by winding the resistance wire. The resistor is made by winding the high resistance alloy wire on the insulating skeleton, and the outside is coated with heat-resistant glaze insulating layer or insulating paint. Winding resistance has low temperature coefficient, high resistance accuracy, good stability, heat resistance and corrosion resistance. It is mainly used as precision high-power resistance. Its disadvantages are poor high-frequency performance and large time constant.
- Carbon synthetic resistor is made of carbon and synthetic plastic.
- The carbon film resistor is made by plating a layer of carbon on the ceramic tube and depositing the crystalline carbon on the ceramic rod skeleton. Carbon film resistor is the most widely used resistor at present because of its low cost, stable performance, wide resistance range and low temperature coefficient and voltage coefficient.
- The metal film resistor is formed by plating 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.
Compared with carbon film resistance, metal film resistance has high precision, good stability, low noise and temperature coefficient. It is widely used in instruments and communication equipment.
- The metal oxide film resistor is formed by plating a layer of tin oxide on the porcelain tube and depositing a layer of metal oxide on the insulating rod. Because it is an oxide itself, it is stable at high temperature, resistant to heat shock and strong load capacity. According to its purpose, it has general purpose, precision, high frequency, high voltage, high resistance, high power and resistance network.
- Fuse resistor: also known as fuse resistor, it plays the dual role of resistance and fuse under normal conditions. When the power of the circuit exceeds the rated power due to fault, it will fuse like a fuse to disconnect the connecting circuit. The fuse resistance is generally small (0.33 Ω ~ 10K Ω) and the power is also small. Common models of fuse resistors include: rf10, symbol type of rf111-5 fuse resistor, rrd0910, rrd0911, etc.
- Sensitive resistor: it means that its resistance value is sensitive to certain physical quantities (such as temperature, humidity, light, voltage, mechanical force, gas concentration, etc.). When these physical quantities change, the resistance value of the sensitive resistor will change with the change of physical quantities, showing different resistance values. According to the sensitivity to different physical quantities, sensitive resistors can be divided into thermal, humidity, photosensitive, pressure sensitive, force sensitive, magnetic and gas sensitive resistors. The materials used in sensitive resistors are almost all semiconductor materials, which are also called semiconductor resistors.
The resistance value of thermistor changes with the change of temperature, and the temperature rise resistance is a negative temperature coefficient (NTC) thermistor. Negative temperature coefficient thermistors are widely used, which can be divided into ordinary negative temperature coefficient thermistors; Voltage stabilizing negative temperature coefficient thermistor; Temperature measurement type negative temperature coefficient thermistor, etc. Photosensitive resistance is that the resistance value of the resistance changes with the intensity of the incident light
When the incident light is enhanced, the photosensitive resistance decreases, and when the incident light is weakened, the resistance increases.