There are various types of fixed resistors, and the choice of material and structure for resistors should depend on the specific requirements of the application circuit. Ordinary wire wound resistors are commonly used in low-frequency circuits or as current limiting resistors, voltage dividing resistors, discharge resistors, or bias resistors for high-power transistors. High precision wire wound resistors are often used in fixed attenuators, resistance boxes, computers, and various precision electronic instruments. Fixed resistor classification: The resistance value of a fixed resistor is fixed and unchanging, and the magnitude of the resistance value is its nominal resistance value. Due to its wide range of applications, there are various types of fixed resistors, which are generally classified according to their constituent materials and structural forms. Different types of fixed resistors have both common resistance performance and different characteristics

(1) Carbon resistors

A mixture of carbon black, resin, clay, etc. is pressed and heat treated to make it.

. Use a color ring on the resistor to represent its resistance value. This type of resistor has a low cost and a wide range of resistance values, but its resistance error and noise voltage are relatively large, and its stability is poor, making it less commonly used

(2) Film resistors

Common film resistors include carbon film resistors, metal film resistors, and metal oxide film resistors.

① Carbon film resistor

Carbon film resistor is a suspension of carbon ink, graphite, and filling material coated on an insulating substrate ceramic rod or tube using an organic adhesive, and then heated and polymerized.

. Gaseous hydrocarbons decompose under high temperature and vacuum, and carbon deposits on ceramic rods or tubes, forming a layer of crystalline carbon film. Changing the thickness of the carbon film or changing the length of the carbon film by grooving can result in different resistance values. Its accuracy and stability are average, but its high-frequency characteristics are good, and it is less affected by voltage and frequency and noise electromotive force. The pulse load is stable, and the resistance range is wide. Due to low production costs and low prices, it is still widely used in consumer electronics products

② Metal film resistor

Metal film resistor is a resistor that uses special metals or alloys as resistance materials and forms a resistance film layer on a ceramic or glass substrate using vacuum evaporation or sputtering technology.

. Vacuum evaporation is the process of heating an alloy in vacuum to evaporate, and then forming a conductive metal film on the surface of a ceramic or glass rod. The resistance value can be adjusted by adjusting the composition of the alloy material, changing the thickness of the film, or controlling the groove. The process is relatively flexible, so it can be made into resistors with good performance and a wide range of resistance values Metal film resistors have superior electrical properties such as heat resistance, noise potential, temperature coefficient, and voltage coefficient compared to carbon film resistors. Compared to carbon film resistors, metal film resistors have smaller volume, lower noise, and better stability, but slightly higher cost. Metal film resistors have been widely used as precision and high stability resistors, and are commonly used in various electronic devices

③ Metal oxide film resistors

Metal oxide film resistors are formed by the decomposition and deposition of hydrolyzable metal salt solutions (such as tin tetrachloride and antimony chloride) on the surface of hot glass or ceramics.

. The performance of resistors varies greatly with different manufacturing conditions. The main characteristics of this type of resistor are high temperature resistance and good chemical stability. This type of resistor has a low resistivity, and the resistance value of low-power resistors does not exceed 100K Ω. Therefore, its application range is limited, but it can be used as a supplement to the low resistance part of metal film resistors. The body of metal oxide film resistors is mostly gray, miniaturized to green or light pink, and is a four color ring resistor. The allowable error level is ± 5% and ± 2%

(3) Wire wound resistor

It is made by winding constantan or nickel chromium alloy resistance wire on a ceramic framework.

. This type of resistor is divided into fixed and variable types. Its characteristics are stable operation, good heat resistance, small error range, and can withstand large instantaneous peak power. Its rated power is generally above 1W and can withstand high temperatures. It can still operate normally in an ambient temperature of 170 ℃. But it has a large volume and low resistance, mostly below 100K Ω. Due to structural reasons, its distributed capacitance and inductance coefficient are relatively large and cannot be applied to high-frequency circuits. This type of resistor is usually used for voltage reduction or load reduction in high-power circuits

(4) Cement resistor