Star one: resistance


As a worker in the electronics industry, resistance is unknown. Its importance is beyond doubt. People say that resistance is the most used component in all electronic circuits.


Resistance, because of the impediment of the substance to the electric current, is called the resistance substance under this action. Resistance will lead to changes in the amount of electronic flow, the smaller the resistance, the greater the amount of electronic flow, and vice versa. A substance with very little resistance or resistance is called an electric conductor, or a conductor. The substance that can not form the current transmission is called an electrical insulator, or an insulator.


In physics, the resistance (Resistance) is used to indicate the magnitude of the impediment of the conductor to the current. The greater the resistance of a conductor, the greater the impediment of the conductor to the current. Different conductors have different resistances. Resistance is a characteristic of the conductor itself. Resistive elements are energy dissipation elements that impede current.


The resistance value of resistance element is generally related to temperature. The physical quantity to measure the resistance affected by temperature is the temperature coefficient, which is defined as the percentage of resistance value changing with temperature increasing by 1%.


The resistor is represented by "R" plus the number in the circuit, for example, R1 indicates a resistance of 1. The main functions of resistance in the circuit are shunting, current limiting, partial voltage, bias and so on.


1. Parameter identification: the unit of resistance is Ohm (omega), and the rate units are: 1000 ohm (K Ohm), mega (M Ohm) and so on. Conversion method is: 1 mega-ohm = 1000 kilo-ohm = 1000 000 ohm resistance parameter marking method has three kinds, namely, direct marking method, color marking method and number marking method. A. Numbering method is mainly used for small volume circuits such as SMT, such as: 472 for 47 *100 (4.7K); 104 for 100Kb, color ring marking method is the most used, for example: four-color ring resistance five-color ring resistance (precision resistance).


2. The relationship between the color mark position and the magnification of the resistor is shown in the following table: Color effective digital magnification allowable deviation (%) silver / X 0.01 (%) gold / x 0.1 (%) black 0 + 0 / Brown 1 x 10 (%) red 2 x 100 (%) Orange 3 x 1000 / yellow 4 x 10000 / Green 5 x 100000 (%) Blue 6 x 1000000 (%) purple 7 x 10000 (%) gray 8 x 10000 0000 / white 9 x1000000000 /.

Star two: capacitor


Capacitance (or electric capacity, Capacitance) refers to the charge storage at a given potential difference; denoted as C, the international unit is Farah (F). Generally speaking, charges move under force in an electric field, and when there is a medium between conductors, it blocks the movement of charges and causes them to accumulate on the conductor; the most common example of accumulation of charges is two parallel metal plates. It is also known as capacitors.


1, capacitance in the circuit is usually expressed in terms of "C" plus numbers (for example, C13 indicates capacitance of 13). Capacitance is composed of two metal films, which are separated by insulating materials in the middle. The main characteristics of capacitors are direct flow and exchange. Capacitance capacity is the size of the capacity to store electrical energy, the impediment of capacitance to AC signal is called capacitance reactance, it is related to the frequency and capacity of AC signal. Capacitance reactance XC = 1/2 PI F C (f denotes the frequency of AC signal, C denotes capacitance capacity) Telephone common capacitors are electrolytic capacitance, porcelain capacitance, patch capacitance, monolithic capacitance, tantalum capacitance and polyester capacitance. Please visit: transmission and distribution network to browse more information.


2. Recognition method: The capacitance identification method and resistance identification method are basically the same, divided into direct standard method, color standard method and number standard method. The basic unit of capacitance is expressed in Farad (F), and other units are: millimeter method (mF), micro method (uF), nanometer method (nF), skin method (pF). Among them: 1 Fara = 103 millimeter method = 106 micro method = 109 nano method = 1012 skin method capacitance of large capacity of its capacity value is directly marked on the capacitor, such as 10 uF / 16V capacitance of small capacity of its capacity value in alphabetical or digital expression of letters on the capacitor: 1m = 1000 uF 1P2 = 1.2PF 1n = 1000PF digital expression: generally three-digit capacity The first two digits represent a valid number, and the third digit is a multiplying rate. For example, 102 for 10 *102 PF = 1000PF 224 for 22 *104PF = 0.22 uF3, capacitance capacity error table symbol F G J K L M allowable error (+1%+2%+5%+10%+15%+20%) For example, a ceramic capacitor for 104J for 0.1 uF, error (+5%).


Star three: crystal diode


Crystal diode (crystaldiode) semiconductor devices at both ends of solid-state electronic devices. The main features of these devices are nonlinear current voltage characteristics. Thereafter, with the development of semiconductor materials and technology, a variety of crystal diodes with various structures and functions were developed by using different semiconductor materials, doping distribution and geometric structures. Manufacturing materials include germanium, silicon and compound semiconductors. Crystal diodes can be used to generate, control, receive, transform, amplify signals and carry out energy conversion.


The crystal diode is commonly used in the circuit as "D" plus numeric representation, for example, D5 means diode with numbered 5.


1. Function: The main characteristic of diode is unidirectional conductivity, that is, under the action of forward voltage, turn-on resistance is very small; and under the action of reverse voltage, turn-on resistance is very large or infinite. Because of these characteristics, diodes are often used in rectifier, isolation, voltage stabilization, polarity protection, coding control, FM modulation and noise suppression circuits in cordless telephones. The crystal diodes used in the telephone can be divided into rectifier diodes (such as 1N4004), isolation diodes (such as 1N4148), Schottky diodes (such as BAT85), light-emitting diodes, voltage regulated diodes and so on.


2. Recognition method: Diode recognition is very simple. The N-pole (negative pole) of low-power diode is marked by a color circle on the surface of the diode. Some diodes also use the special symbol of the diode to represent the P-pole (positive pole) or N-pole (negative pole), and some use the symbol "P", "N" to determine the polarity of the diode. The positive and negative poles of light emitting diodes can be identified from the length of pins. The long feet are positive and the short feet are negative.


3. Test Notes: When the diode is measured with a digital multimeter, the red meter is connected with the positive pole of the diode and the black meter is connected with the negative pole of the diode. At this point, the measured resistance is the positive conduction resistance of the diode, which is just the opposite of the dial-pen connection of the pointer multimeter.


4. The voltage withstand comparison of the commonly used 1N4000 series diodes is as follows: Model 1N40011N40021N4003 1N4004 1N40051 N40061N4007 voltage withstand (V) 50 100 200 400 600 800 1000 current (A) are 1.

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