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What are the basic knowledge of electronic components


Identify common parts:

1. Resistance

The resistance in the circuit is represented by R and a number, such as R15 means a resistance of 15. The main functions of resistors in a circuit are shunt, current limit, voltage divider, bias, filter (used with capacitors) and resistor matching.

Parameter identification: The unit of resistance is ohm (ω), and the unit of magnification is kilo-ohm (Kω), megohm (Mω), etc. The conversion method is: 1 megohm = 1000 kiloohms = 10,000 euros.

There are three methods for marking the parameters of the resistance, namely the direct marking method, the color marking method and the numerical marking method.

Digital magnification tolerance of valid colors (%)



Black 0100/Black.

Brown 1101±1.

2102 ± 2 red.


4104 yellow

5105±0.5 green

Blue 6106 ± 0.2.

Violet 7107 ± 0.1.


White 9109+5-20.

Colorless //±20.


2. Capacitance

1. Capacitors are usually denoted by a C and a number (for example, C25 means a capacitor numbered 25). A capacitor consists of two parts close to a metal film separated by an insulating material. Capacitors are mainly characterized by DC communication.

The size of the capacitor refers to the size of the stored electrical energy. Capacitance blocking an AC signal is called capacitive reactance and is related to the frequency and capacitance of the AC signal. Capacitance XC=1/2πFC.

(f is the frequency of the AC signal, C is the capacitance)

The types of capacitors commonly used in telephones include electrolytic capacitors, chip capacitors, monolithic capacitors, tantalum capacitors, polyester capacitors, etc.


2. Identification method: The identification method of capacitance is basically the same as that of resistance, which is divided into direct marking method, color marking method and number marking method. The basic unit of a capacitor is expressed in farads (F), and other units include: m-farads (mf), microfarads (uf), nanofarads (nf), and picofarads (pf).

Among them: 1 farad = 103m method = 106 microfarads = 109 nanofarads = 1012 picofarads. The capacitance value is directly marked on the capacitor, such as 10uf/16V.

The capacity value of small-capacity capacitors is represented by letters or numbers.

Letter notation: 1m=1000u1P2=1.2PF1n=1000PF.

Digital representation: The capacity is generally represented by three digits, the first two digits represent significant digits, and the third digit is the magnification.

For example: 102 means 10×102PF=1000PF224 means 22×104PF=0.22UF.


3. Capacitance error table.

FGJKLM symbol.

For example, a capacitor of 104J means the capacity is 0.1uf. The error is ±5%.


4. Fault characteristics.

In actual maintenance, capacitor failures are mainly manifested as:

(1) Corrosion of pins leads to open circuit failure.

(2) Open circuit failure of desoldering and virtual soldering.

(3) Small capacity or open circuit failure after water leakage.

(4) Leakage. Serious leakage and breakdown faults.

Third, the crystal diode.

The crystal diode of D plus number is commonly used in the circuit, such as: D5 is a diode of 5.


1. Function: The main feature of the diode is unidirectional conduction, that is, under the action of forward voltage, the conduction resistance is very small; under the action of reverse voltage, the conduction resistance is very large or infinite. Due to the above characteristics of diodes, cordless phones are often used in circuits such as rectification, isolation, voltage regulation, polarity protection, coding control, frequency modulation regulation, and noise suppression.

The crystal diodes used in telephones can be divided into: rectifier diodes (such as 1N4004), isolation diodes (such as 1N4148), Schottky diodes (such as BAT85), light-emitting diodes, Zener diodes, etc.


2. Identification method: The identification of diodes is very simple. The N pole (negative pole) of the low-power diode is mainly marked on the appearance of the diode. Some diodes also use a special symbol for the diode to denote either the P pole (positive pole) or the N pole (negative pole), and label the symbols as P and N to determine the polarity of the diode. The positive and negative poles of the light-emitting diode can be determined from the length of the pins. The long pin is positive and the short pin is negative.


3. Test precautions: When measuring the diode with a digital multimeter, the red test lead is connected to the positive electrode of the diode, and the black test lead is connected to the negative electrode of the diode. The resistance value measured at this time is the forward resistance value of the diode, which is exactly the opposite of the connection method of the test lead of the pointer multimeter.

Fourth, the Zener diode.

Zener diodes commonly used in circuits such as ZD5 are represented as 5 Zener tubes.

1. The voltage regulation principle of the Zener diode: The characteristic of the Zener diode is that the voltage at both ends remains basically unchanged. In this way, when the Zener tube is connected to the circuit, if the power supply voltage fluctuates or other reasons cause the voltage at each point in the circuit to change, the voltage across the load remains basically unchanged.


5. Inductance


L plus a number indicates inductance, such as: L6 indicates No. 6 inductance.

The inductor coil is a certain number of insulated wires wound on the insulating skeleton.

DC can pass through the coil. The DC resistance is the resistance of the wire itself, and the voltage drop is very small; when the AC signal passes through the coil, a self-inductive potential will be generated at both ends of the coil. The direction of the self-induced potential is opposite to the external voltage, blocking the exchange. Therefore, inductance is characterized by AC through DC resistance. The higher the frequency, the higher the coil impedance. Inductance can form an oscillating circuit with capacitors in the circuit.

Inductors generally have direct marking method and color marking method, similar to resistance. Such as brown, black, gold. Gold indicates an inductance of 1uH (5% error).

The basic units of inductance are: Henry (H) conversion units are: 1H=103mH=106uH.

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