Date：2016-09-02 Categories：Industry News Hits：404
Identification of common components
1、 Resistance
Resistance in the circuit with "R" plus a number, such as: R15 for the number of 15 resistance. The main functions of resistance in the circuit are shunt, current limiting, voltage dividing, bias, filtering (combined with capacitor) and impedance matching.
Parameter identification: the unit of resistance is Ohm (Ω), and the unit of magnification is kiloohm (K Ω), megaohm (m Ω), etc. The conversion method is: 1 megohm = 1000 kilo ohm = 1000000 ohm
There are three kinds of marking methods of resistance parameters, namely direct marking method, color coding method and number standard method.
The digital standard method is mainly used for small volume circuits such as chip, etc
472 means 47 × 102 Ω (i.e. 4.7K); 104 indicates that 100k color ring labeling method is most commonly used. Here are some examples:
The relationship between the color mark position and magnification of the four color ring resistance (precision resistance) resistance is shown in the table below
Allowable deviation of effective number ratio of color
Silver / 10-2 ± 10
Gold / 10-1 ± 5
Black 0 100/
Brown 1 101 ± 1
Red 2 102 ± 2
Orange 3 103/
Yellow 4 104/
Green 5 105 ± 0.5
Blue 6 106 ± 0.2
Purple 7 107 ± 0.1
Grey 8 108/
White 9 109 + 5 to - 20
Colorless / / ± 20
2、 Capacitance
1. Capacitance in the circuit is generally represented by "C" plus a number (for example, C25 represents the capacitance numbered 25). A capacitor is a component composed of two metal films close to each other and separated by insulating materials. The main characteristic of capacitor is that it flows through AC directly.
The size of capacitance is the size of the stored electric energy. The blocking effect of capacitance on AC signal is called capacitive reactance, which is related to the frequency and capacitance of AC signal. Capacitance reactance XC = 1 / 2 π F C
(F is the frequency of the AC signal, C is the capacitance capacity)
The types of capacitors commonly used in telephone sets include electrolytic capacitor, ceramic chip capacitor, chip capacitor, monolith capacitor, tantalum capacitor and polyester capacitor.
2. Identification method: the identification method of capacitance is basically the same as that of resistance, which can be divided into three types: direct labeling method, color coding method and number standard method. The basic unit of capacitance is expressed in farad (f), and other units are: millimetre (MF), micromethod (UF), nanomethod (NF) and skin method (PF).
Among them: 1 farad = 103 MF = 106 MF = 109 NF = 1012 PFA, the capacitance value of large capacitance is directly indicated on the capacitance, such as 10 UF / 16 v
The capacitance value of a small capacitance is represented by letters or numbers on the capacitance
Alphabetic representation: 1m = 1000 UF 1P2 = 1.2pF 1n = 1000pf
Digital representation: generally, three digits are used to represent the capacity, the first two digits represent the effective number, and the third digit is the multiplier.
For example: 102 means 10 × 102pf = 1000pf, 224 means 22 × 104pf = 0.22uf
3. Capacitance error table
Symbol fgjklm
The allowable error is ± 1% ± 2% ± 5% ± 10% ± 15% ± 20%
For example, if the capacitance of a ceramic chip is 104j, the capacity is 0.1 UF, and the error is ± 5%.
4. Fault characteristics
In practical maintenance, the main faults of capacitor are as follows:
(1) Open circuit fault caused by pin corrosion.
(2) Open circuit fault of desoldering and false soldering.
(3) Leakage causes small capacity or open circuit fault.
(4) Leakage, serious leakage and breakdown fault.
3、 Crystal diode
Crystal diode in the circuit commonly used "d" plus number, such as: D5 refers to the number of 5 diode.
1. Function: the main characteristic of diode is unidirectional conductivity, that is, under the action of forward voltage, the on resistance is very small; while under the action of reverse voltage, the on resistance is very large or infinite. Because of the above characteristics, diodes are often used in rectifying, isolating, stabilizing voltage, polarity protection, coding control, frequency modulation and silencing circuits in cordless telephone sets.
The crystal diodes used in telephone can be divided into rectifier diodes (such as 1N4004), isolation diodes (such as 1N4148), Schottky diodes (such as BAT85), light-emitting diodes, voltage stabilizing diodes, etc.
2. Identification method: the identification of diode is very simple. Most of the N-pole (negative pole) of low-power diode is marked with a color circle on the outside of the diode. Some diodes also use the special symbol of the diode to indicate the P-pole (positive pole) or N-pole (negative pole), and some use the symbol marks "P" and "n" to determine the diode polarity. The positive and negative poles of LED can be identified by the length of the pin. The long pin is positive and the short pin is negative.
3. Test precautions: when using a digital multimeter to test the diode, the red probe is connected to the positive pole of the diode, and the black probe is connected to the negative pole of the diode. At this time, the measured resistance is the positive conduction resistance of the diode, which is just the opposite of the connection method of the pointer multimeter.
4. The voltage withstand comparison of commonly used 1n4000 series diodes is as follows:
Model 1N4001 1N4002 1N4003 1N4004 1N4005 1N4006 1N4007
Withstand voltage (V) 50 100 200 400 600 800 1000
The current (a) is 1
4、 Zener diode
Zener diode in the circuit commonly used "ZD" plus digital representation, such as: zd5 refers to the number of 5 Zener tube.
1. The voltage stabilizing principle of voltage stabilizing diode: the characteristic of voltage stabilizing diode is that after breakdown, the voltage at both ends basically remains unchanged. In this way, when the voltage regulator is connected to the circuit, the voltage at both ends of the load will remain basically unchanged if the power supply voltage fluctuates or the voltage at each point in the circuit changes due to other reasons.
2. Fault characteristics: voltage regulator diode fault main