Many items in everyday life have resistance, but some are very large and some are small. The resistor we are talking about here is a resistor in an electronic device, but the resistor is often referred to as a resistor. Resistor is almost an indispensable part of any electronic circuit. As the name suggests, the role of the resistor is to block the action of electrons. The main functions in the circuit are: buffer, load, voltage division and shunt, protection and so on.
The resistance value of the resistance element is generally related to temperature, material, length, and cross-sectional area. The physical quantity that measures the magnitude of the resistance of the resistance is the temperature coefficient, which is defined as the percentage change of the resistance value for every 1 °C increase in temperature. The main physical characteristic of a resistor is that it converts electrical energy into thermal energy. It can also be said that it is an energy-consuming component through which current generates internal energy. The resistor usually functions as a partial pressure or a shunt in the circuit. For signals, both AC and DC signals can pass through the resistor.
Development of Resistance In 1885, British C. Bradley invented molded carbon core solid resistors. In 1897, British T. Gabriel and A. Harris made carbon film resistors with carbon ink. From 1913 to 1919, W. Swann of the United Kingdom and F. Kruger of Germany invented metal film resistors. In 1925, the German company Siemens-Halsk invented the thermal decomposition carbon film resistor, breaking the monopoly market of carbon solid core resistors. After the advent of the transistor, the requirements for miniaturization and resistance stability of the resistor are stricter, which promotes the development of various new types of resistors. Bell Labs in the United States developed a TaN resistor in 1959. Since the 1960s, new technologies such as roller magnetron sputtering and laser resistance trimming have been adopted, and some products have been developed in terms of planarization, integration, miniaturization and flaking.
The composition of the resistor <br> A two-terminal electronic component made of a resistive material and having a certain structure and capable of limiting the passage of current in the circuit. A resistor cannot be changed and is called a fixed resistor. A variable resistance is called a potentiometer or a variable resistor. The ideal resistor is linear, ie the instantaneous current through the resistor is proportional to the applied instantaneous voltage. Some special resistors, such as thermistors, varistors, and sensitive components, have a non-linear relationship between voltage and current. Resistors are the most widely used components in electronic circuits. They are usually formed in different series according to power and resistance for circuit designers to choose. The resistor is mainly used in the circuit to regulate and stabilize the current and voltage. It can be used as a shunt and a voltage divider, or as a circuit matching load. According to the circuit requirements, it can also be used for amplifying the circuit's negative feedback or positive feedback, voltage-current conversion, input voltage or current protection components, and RC circuit as oscillation, filtering, bypass, differential, integral and time constant. Components, etc.
Classification of resistors
Carbon Film Resistors <br> It is a carbon film fixed resistor with the largest amount of electronics, electrical appliances and information products, the cheapest price and high reliability of quality stability. The resistor separates the carbon of the organic compound in a high-temperature vacuum, and the carbon film closely attached to the surface of the ceramic rod is a resistor, and is thinned by a suitable joint, and is coated with an epoxy resin seal on the surface. Advantages: simple production, low cost Disadvantages: poor stability, high noise, large error Metal oxide film resistors with the development of electronic equipment, its components are also tend to be smaller, lighter and more durable. The resistor works at high temperature, and has long-term stability and stability. The unit area of ​​the film of the resistor must be loaded with high power to meet the requirements of its work, and the metal oxide film resistor is a suitable resistor. Advantages: small size High precision, good stability, low noise, small inductance. Disadvantages: high cost wirewound resistor, non-inductive wirewound resistor wound on the asexual heat-resistant porcelain body, the surface is coated with heat resistance, moisture resistance, no Corrosive non-combustible coating, protected. Its characteristics are as follows: excellent heat resistance, small temperature coefficient, light weight, short-time overload, low noise, and small change in resistance over the years. Non-inductive wirewound resistor (NKNP) has the basic characteristics of wirewound resistor (KNP), plus the advantages of low inductance. Advantages: Power shortage: Inductance, large volume, not suitable for resistance with large resistance<br> Cement type wirewound resistor <br> The wire is wound around a non-salty heat-resistant porcelain piece or fixed with a resistor such as an oxide film resistor, and is protected by a heat-resistant, moisture-resistant and corrosion-resistant material. The cement type resistor is formed by placing the resistor body in a square porcelain frame and filling it with a special non-combustible heat-resistant cement. It has the advantages of high power resistance, easy heat dissipation and high stability. It has the advantages of large power: it has inductance, large volume, and it is not suitable for resistors with large resistance.
Two large resistance reading methods
First, the color ring resistance reading method
The color ring resistance is also a common in-line resistor, and is generally divided into a four-color ring and a five-color ring according to the number of color rings. Each color circle represents a different meaning, as shown in the following figure.
Four color ring reading method first color ring: the first significant number;
The second color circle: the second significant number;
The third color circle: indicates the magnification;
The fourth color circle: indicates the error, that is, the accuracy;
Four color ring examples:
The first color circle: yellow, representing 4;
The second color circle: purple, representing 7;
The third color circle: red, representing the square of 10;
The fourth color circle: brown, representing ±1%;
Therefore, the resistance of this resistor is 47 & TImes; 10 ^ 2 = 4700 Ω = 4.7 K ohms with an error of ± 1%.
The fifth color ring reading method first color ring: the first significant number;
The second color circle: the second significant number;
The third color circle: the third significant number;
The fourth color circle: indicates the magnification;
The fifth color circle: indicates the error, that is, the accuracy;
Five color ring examples:
The first color circle: yellow, representing 4;
The second color circle: purple, representing 7;
The third color ring: black, representing 0;
The fourth color circle: brown, representing 10;
The fifth color circle: brown, representing ±1%;
Therefore, the resistance of this resistor is 470 & TImes; 10 = 4700 Ω = 4.7 K ohms with an error of ± 1%.
For the reading method of the color ring resistance, we can only understand it. In reality, no one will remember the value represented by the color ring, and now many color rings are not standard, which brings interference to the identification. . If you encounter someone in real life who can correctly read the resistance value without using any tools and only through the color circle, then call him the god.
Second, the chip resistance reading method <br> The surface of the chip resistor has a digital silk screen, as long as the meaning of the number is clear, the resistance and accuracy can be determined.
Chip resistor resistance error accuracy is ±1%, ±2%, ±5%, ±10% accuracy, the most commonly used is ±1% and ±5%, 5% accuracy is represented by three digits, The 1% accuracy is represented by four digits. Examples are as follows:
The silkscreen of the resistive surface is 103:
The first two digits 10 represent the significant digits, and the third digit 3 represents the magnification, which is 10^3, so the resistance of the 103 resistor is 10 & TImes; 10^3 = 10000 Ω = 10K, and the accuracy is 5%.
The silkscreen of the resistive surface is 1502:
The first three digits 150 represent the effective digits, and the fourth digit 2 represents the magnification, ie 10^2, so the resistance of the 1502 resistor is 150 & TImes; 10^2 = 15000 Ω = 15K with an accuracy of 1%.
There is also a case where the screen printing tape R is used, which means a resistor with a decimal number, and the position where R is located is the position of the decimal point.
The silk screen of the resistive surface is R047:
The position where R is located indicates the position of the decimal point, and R047 indicates the resistance of 0.047 ohm.
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