Resistors, commonly referred to as resistors, are one of the most common and widely used electronic components. It accounts for more than 30% of the total number of components in electronic equipment. Our understanding of resistors cannot stay at the level of "R=U/I". Understanding the manufacturing process of resistors is very important for us to learn and understand the main parameters of resistors, and to choose and use resistors correctly. Resistors are made of materials with high resistivity, which play a role in stabilizing or regulating current and voltage in circuits.
1. Resistor Classification
2.Resistor Classification Introduction
2.1 Carbon film resistors
Carbon film resistors are hydrocarbons separated in high temperature and vacuum furnaces, and then carbon is deposited on the surface of the ceramic substrate to form a carbon film with a certain resistance value (the resistance value can be obtained by changing the thickness or length of the carbon film) (resistor body), a resistor produced by cutting it thin after adding appropriate joints, and coating the surface with epoxy resin for sealing protection, so it is also called thermal decomposition carbon film resistor. The main characteristics of carbon film resistors are relatively good high frequency characteristics, wide resistance range, and low price, but the resistance error is large. It is the general-purpose resistor with the largest production volume and the widest application in our country. It is widely used in electronic products such as tape recorders and TV sets.
2.2 Metal film resistors
Metal film resistors are made by depositing a layer of alloy powder on a porcelain substrate under vacuum conditions. Different resistance values can be obtained by changing the thickness, length or groove of the metal film. Metal film resistors mainly include metal film resistors (CN), metal oxide film resistors (RS) and metal glaze film resistors (K). Due to the advantages of high power, low noise, small temperature coefficient, high precision, good high-frequency characteristics, and wide resistance range, metal film resistors are widely used in high-end equipment such as high-end audio, computers, test instruments, and automation controls. Of course, there are also precision metal film resistors, which use nickel or similar alloy vacuum plating technology to deposit resistive materials on the surface of white porcelain rods, and then cut and adjust the resistance to achieve the final required precision resistance. Precision metal film resistors have precise resistance and small tolerance range, and are mainly used in occasions that require more precise resistance.
2.3 Impact-resistant glass glaze film power resistors
Impact-resistant glass glaze film power resistor is a kind of resistor produced by plating metal glass glaze on the magnetic rod. It has excellent impact resistance characteristics and high temperature stability, and is mainly used in high-power equipment.
2.4 Wirewound resistors
Wire-wound resistors are made by winding resistance wires (constantan wire or nickel-chromium alloy wire) on a heat-resistant ceramic skeleton, and the surface is coated with heat-resistant, moisture-resistant, non-corrosive non-combustible protective coating. This kind of resistance is divided into two types: fixed resistance and variable resistance. It is characterized by good heat resistance, small temperature coefficient, light weight, short-time overload resistance, low noise, stable resistance, low inductance, etc., but its high-frequency characteristics are poor, so it is suitable for high-power applications. The rated power is generally above 1W.
2.5 Cement resistance
Cement resistance is also a kind of wire-wound resistance, which is made by winding resistance wire on heat-resistant ceramic parts, and protecting and fixing it with heat-resistant, moisture-resistant and corrosion-resistant materials on the outside. Cement resistors are usually made by putting the resistor body in a square porcelain frame and filling and sealing it with special non-combustible and heat-resistant cement. Because its shape is like a white rectangular cement block, it is called cement resistor. Cement resistors have the characteristics of high power, good heat dissipation, high stability, moisture resistance, and shock resistance. It is mainly used in high-power circuits, such as overcurrent detection and protection circuits of power circuits, and power output circuits of audio power amplifiers. The disadvantage of cement resistance is that it is large in size, high in heat when used, easy to emit, and its precision often cannot meet the requirements of use. When high power, small size resistance, or high precision and fast heat dissipation are required, the cement resistance can be replaced by JEPSUN power resistance. Cement resistor shells are generally made of ceramics, and its main component is alumina (A1.0,), commonly known as corundum porcelain, which has the characteristics of fast heat dissipation and high strength.
2.6 Fuse resistor
Fused resistor, also known as fuse resistor or fuse resistor, is a special component with dual functions of resistor and fuse. It is represented by the letter "RF" or "R" in the circuit. It can be used as a resistor at ordinary times, and once the current is abnormal, it will play the role of a fuse to protect machinery and equipment. Most of the fuse resistors are gray, and the resistance value is indicated by a color ring or a number, and the rated power is determined by the size of the resistor. Divided into two kinds of resettable fuse resistors and one-time fuse resistors. Mainly used in power output circuits. The resistance value of the insurance resistor is generally small (a few ohms to tens of ohms), and the power is also small (1/8 ~ 1W). When a short-circuit fault occurs in the load circuit and an overcurrent occurs, the temperature of the insurance resistor will rise to 500C ~ 600C in a short period of time. At this time, the resistance layer will be peeled off by heat and blown, thereby protecting other important components. function to achieve the purpose of improving the safety of the whole machine.
2.7 Network resistance
Network resistance is also called exclusion. The network resistor is a compound resistor made by packaging multiple resistors together and combining them. Network resistors have the advantages of convenient assembly and high installation density, and have been widely used in electronic circuits.
2.8 Surface Mount Resistors
Surface mount resistors are also called leadless resistors, chip resistors, chip resistors, and SMC resistors. There are two main types of surface mount resistors, rectangular and cylindrical. Rectangular surface mount resistors are mainly composed of ceramic substrates, resistive films, protective layers, and metal terminal electrodes. The ceramic substrate is generally made of 96% aluminum oxide (A1.0,) ceramics: the resistance film is usually printed on the substrate with a resistance paste composed of Ruo., and then sintered: the protective layer covering the resistance film Generally, glass paste material is used for printing and then fired into glaze: the terminal electrode is composed of three layers of materials: the inner layer (that is, the part of the contact resistance film) adopts Ag-Pd alloy with small contact resistance and strong adhesion; the middle layer is Ni, mainly Used to prevent the terminal electrode from detaching: the outer layer is a solderable layer composed of Sn or Sn-Pb or Sn-Ce alloy. Cylindrical surface mount resistors are coated with metal or carbon resistance film on the high alumina ceramic substrate, and then press metal electrode caps on both ends, and then brush a layer of heat-resistant insulating varnish after confirming the resistance by engraving thread grooves. Spray color-coded marks on the surface
2.9 Sensitive resistor
Sensitive resistors refer to resistors whose device characteristics are sensitive to temperature, voltage, humidity, light, gas, magnetic field, pressure, etc. The symbol of the sensitive resistor is to add a slash to the symbol of the ordinary resistor, and mark the type of the sensitive resistor beside it, such as t.v.
Thermistors are made of heat-sensitive semiconductor materials through a certain sintering process. When this type of resistor is heated, its resistance value changes with temperature. It has positive and negative temperature coefficient types, users should pay attention to this point when using it. The positive temperature type resistor is represented by the letter PTC. When the resistance reaches a certain temperature, the resistance value decreases slowly with the increase of temperature. When the temperature exceeds this temperature, the resistance value increases sharply. This specific temperature point is called the Curie point. The Curie point of PTC thermistor can be changed by changing the proportion of each component in its material. It is widely used in home appliances, such as degaussing resistors for color TVs, thermostats for rice cookers, etc.: Negative temperature resistors are represented by the letter NTC, and their resistance decreases with increasing temperature. According to this characteristic, it can be used to control the size and on-off of current in the control circuit, and it is often used as a temperature-sensing element in circuits such as temperature measurement, temperature control, compensation, and protection.
Photoresistor, also known as photoresistor, is a resistor whose resistance value changes with the intensity of incident light, which is made of photosensitive semiconductor material such as vulcanization pot or vulcanization secret. Decrease, the human light is weak, and the resistance increases. Photoresistors are generally used for light measurement, light control, and photoelectric conversion. Photoresistors are made into thin sheets to absorb more light energy. When it is irradiated by light, electron-hole pairs are excited in the semiconductor chip (photosensitive layer) to participate in conduction, so that the current in the circuit is enhanced. The materials used to make photoresistors are mainly semiconductors such as metal sulfides, selenides, and thiamines. According to the spectral characteristics of photoresistors, it can be divided into three types of photoresistors: ultraviolet photoresistors, infrared photoresistors, and visible light photoresistors.
The varistor is mainly a semiconductor ceramic device made of silicon carbide and zinc oxide as the main material, and is a non-linear resistance device that is very sensitive to voltage changes. Within a certain temperature and a certain voltage range, when the external voltage increases, the resistance value decreases; when the external voltage decreases, the resistance value increases instead, so the varistor can keep the voltage stable at all times, and can be used in electronic circuits In switching circuits, overvoltage protection, noise cancellation circuits and absorption circuits.
Gas-sensitive resistors are made of certain semiconductors that absorb a certain gas and undergo redox reactions. The main components are metal oxides. There are metal oxide gas-sensitive resistors, composite oxide gas-sensitive resistors, ceramic gas-sensitive resistors, etc.
The force-sensitive resistor is a resistor whose resistance value changes with pressure, and is called a piezoresistor abroad. The piezoresistive effect is the effect that the resistivity of semiconductor materials changes with mechanical pressure. It can be made into various torque meters, semiconductor microphones, and pressure sensors. The main varieties are silicon force sensitive resistors and selenium broken alloy force sensitive resistors. Relatively speaking, alloy resistors have higher sensitivity. The main parameters of force sensitive resistors are temperature coefficient, sensitivity coefficient, sensitivity temperature coefficient and temperature zero drift. (1) Temperature coefficient: The resistance value change of the force-sensitive resistor is related to the temperature. The temperature change is 1C, and the percentage of the resistance value change is called the temperature coefficient. (2) Sensitivity coefficient: refers to the relationship between the deformation and the resistance value of the force-sensitive resistor. The relationship between the deformation and the resistance value change satisfies: Ar /r-k1 /1, which is the sensitivity coefficient. (3) Sensitivity temperature coefficient: When the temperature rises, the sensitivity of the force-sensitive resistor decreases, and the percentage of the sensitivity coefficient decreases for every 1C increase in temperature. (4) Temperature zero drift: within the ambient temperature range, when the ambient temperature changes by 1C, the percentage of the zero output change and the rated output caused by it
2.10 Potentiometer
The potentiometer is actually a variable resistor, which is often used to change and adjust the resistance value in the circuit, such as the brightness adjustment in the TV, the volume adjustment of the loudspeaker, etc., are all realized through it. According to actual needs, there are no less than dozens of types of potentiometers, but their basic principles are similar. The resistor body of the potentiometer is made by coating a layer of carbon film on a horseshoe-shaped paper glue board. The common ones are carbon film potentiometer and wire wound potentiometer. The relationship between the resistance value change of the potentiometer and the position of the intermediate contact has several types: linear, logarithmic, and exponential. The linear type is suitable for voltage division, current adjustment, and bias current adjustment: logarithmic and exponential types are often used to adjust the tone to meet the physiological characteristics of the human ear.
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