Application points and identification methods of t

Application points and identification methods of common electronic components

I. resistance

resistance is represented by "R" plus numbers in the circuit, for example, R1 represents the resistance numbered 1. The main functions of resistance in the circuit are shunting, current limiting, voltage dividing, bias, etc

1. Parameter identification:

the unit of resistance is Ohm (Ω), and the magnification unit is kiloohm (K Ω), megaohm (m Ω), etc. The conversion method is:

1 megohm =1000 kiloohm = ohm

there are three methods to mark the parameters of resistance, namely, direct marking method, color marking method and number marking method

a, the digital scaling method is mainly used for small volume circuits such as patch, for example:

472 means 47 × 100 Ω (i.e. 4.7K); 104 means 100k

B. the color ring marking method is most used. Now examples are as follows:

four color ring resistance five color ring resistance (precision resistance)

2 The relationship between the color scale position and magnification of the resistance is shown in the following table:

Color effective digit magnification allowable deviation (%)

Silver/x0.01 ± 10

Gold/x0.1 ± 5

black 0 +0/

Brown 1 X10 ± 1

Red 2 X100 ± 2

Orange 3 X1000/

yellow 4 x10000/

Green 5 x10000 ± 0.5

Blue 6 x ± 0.2

purple 7 x ± 0.1

gray 8 x/

White 9 x/

II Capacitance

1. Capacitance is generally represented by "C" plus numbers in the circuit (for example, C13 represents the capacitance numbered 13). Capacitance is an element composed of two metal films close together and separated by insulating materials. The main characteristic of the capacitor is to isolate direct current AC

the size of capacitance is the size of electric energy that can be stored. The blocking effect of capacitance on AC signal is called capacitive reactance, which is related to the frequency and capacitance of AC signal

capacitive reactance xc=1/2 π F C (f represents the frequency of AC signal, C represents the capacitance)

the types of capacitors commonly used in machines include electrolytic capacitors, ceramic chip capacitors, chip capacitors, monolith capacitors, tantalum capacitors and polyester capacitors

2. Identification method: the identification method of capacitance is basically the same as that of resistance, which is divided into three methods: direct calibration method, color coding method and number coding method

the basic unit of capacitance is expressed in farad (f), and other units are: milli method (MF), micro method (UF), nano method (NF), skin method (PF)

among them: 1 farad =103 millimethod =106 micro method =109 nanomethod =1012 PI method

the capacity value of the capacitance with large capacity is directly marked on the capacitance, such as 10 uf/16v

the capacity value of the capacitance with small capacity is represented by letters or numbers on the capacitance

letter representation: 1m=1000 UF 1p2= 1.2pF 1n=1000pf

number representation: generally, three digits are used to represent the capacity, the first two digits represent the significant digits, and the third digit is the magnification

for example: 102 means 10 × 102pf=1000pf 224 means 22 × 104pf=0.22 uf

3. Capacitance error table

symbol F G J KL m

allowable error ± 1% ± 2% ± 5% ± 10% ± 15% ± 20%

for example, a ceramic chip capacitance of 104j means that the capacity is 0 1 UF, the error is ± 5%

III. crystal diode

crystal diode is usually represented by "d" plus numbers in the circuit, for example, D5 represents the diode numbered 5

1. Function: the main characteristic of diode is unidirectional conductivity, that is, under the action of forward voltage, the on resistance is very small; Under the action of reverse voltage, the on resistance is extremely large or infinite. Because the diode has the above characteristics, it is often used in the circuits of rectification, isolation, voltage stabilization, polarity protection, coding control, frequency modulation and noise suppression in cordless machines. The crystal diodes used in the machine 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 small power diodes is mostly marked with a color circle on the surface of diodes. Some diodes also use special symbols for diodes to represent P pole (positive pole) or N pole (negative pole), and some use symbols marked as "P" and "n" to determine the polarity of diodes. The positive and negative poles of the LED can be identified from 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 measure 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 to the probe 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

voltage withstand (V) 50 100 200 400 600 800 1000

current (a) is 1

IV. zener diode

zener diode is commonly represented by "ZD" plus numbers in the circuit, for example, zd5 represents the zener tube with number 5

1. Voltage stabilizing principle of Zener diode: the characteristic of Zener diode is that after breakdown, the voltage at both ends basically remains unchanged. This is to share with you the factors that need to be considered in the protection, maintenance and selection of material change experimental machine. In this way, when the regulator is connected to the circuit, if the voltage at each point in the circuit changes due to the fluctuation of the power supply voltage or other reasons, the voltage at both ends of the load will basically remain unchanged

2. Fault characteristics: the fault of Zener diode is mainly manifested in open circuit, short circuit and unstable Zener value. Among the three kinds of faults, the former one shows the rise of power supply voltage; The latter two faults show that the power supply voltage becomes low to zero volts or the output is unstable. The models and regulated values of commonly used zener diodes are shown in the following table:

model 1n4728 1n4729 please check whether the power supply voltage is ac220v1n4730 1n4732 1n4733 1n4734 1n4735 1n4744 1n4750 1n4751 1n4761

regulated value 3.3V 3.6V 3.9v 4.7V 5.1V 5.6v 6.2V 15V 27V 30V 75V

v. inductance

inductance is usually expressed by "L" plus numbers in the circuit, and for example, L6 represents the inductance numbered 6

inductance coil is made by winding the insulated wire on the insulated skeleton for a certain number of turns

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, the self induced electromotive force will be generated at both ends of the coil. The direction of the self induced electromotive force is opposite to the direction of the applied voltage, which hinders the passage of AC. therefore, the characteristic of the inductance is to connect DC resistance to ac. the higher the frequency, the greater the coil impedance. The improved component quality of inductance in the circuit can form an oscillation circuit with capacitance. Inductance generally has direct marking method and color marking method, which is similar to resistance. For example, brown, black, gold and gold represent 1uh (error 5%)

inductance

the basic unit of inductance is Heng (H). The conversion units are: 1h=103mh=106uh

VI. varactor

varactor is a special diode specially designed according to the principle that the junction capacitance of the "PN junction" inside the ordinary diode can change with the change of the applied reverse voltage. Varactor diode is mainly used in the high-frequency modulation circuit of cordless machine or landline machine to realize the modulation of low-frequency signal to high-frequency signal and send it out. In the working state, the modulation voltage of the varactor is generally added to the negative pole, so that the internal junction capacitance of the varactor changes with the modulation voltage

varactor diode failure is mainly manifested in leakage or poor performance:

(1) when leakage occurs, the high-frequency modulation circuit will not work or the modulation performance will become poor

(2) when the varactor performance becomes poor, the operation of the high-frequency modulation circuit is unstable, causing distortion after the modulated high-frequency signal is sent to the other party and received by the other party

in case of one of the above situations, the varactor of the same model should be replaced

VII. Crystal triode

crystal triode is usually represented by "Q" plus numbers in the circuit, for example, Q17 represents the triode numbered 17

1. Characteristics: crystal triode (referred to as triode) is a special device with two PN junctions inside and amplification ability. It can be divided into two types: NPN type and PNP type. These two types of triodes can complement each other in terms of working characteristics. The so-called opposite transistor in OTL circuit is used by PNP type and NPN type in pairs

2. Crystal triodes are mainly used for amplification in amplification circuits. There are three connection methods in common circuits. In order to facilitate comparison, the characteristics of the three transistor connection circuits are listed in the table below for your reference

Name: common emitter circuit, common collector circuit (emitter output) common base circuit

input impedance: medium (hundreds of euros to thousands of euros) large (more than tens of thousands of euros) small (a few euros to tens of euros)

output impedance: medium (thousands of euros to tens of thousands of euros) small (a few euros to tens of thousands of euros) large (tens of thousands of euros to hundreds of thousands of euros)

voltage magnification: size (less than 1 and close to 1) Large

current magnification: large (dozens) large (dozens) small (less than 1 and close to 1)

power magnification: large (about 30 ~ 40 dB) small (about 10 dB) medium (about 15 ~ 20 dB)

frequency characteristics: high frequency difference good

Application: intermediate stage of multi-stage amplifier, low-frequency amplification input stage, output stage or high-frequency or broadband circuit for impedance matching and constant current source circuit

VIII Field effect transistor amplifier

1, field effect transistor has the advantages of high input impedance and low noise, so it is also widely used in various electronic devices. In particular, using FET as the input stage of the whole electronic equipment can obtain the performance that is difficult to achieve when all switches of general crystal are turned off

2. FET is divided into junction type and insulated grid type, and its control principle is the same. As shown in the figure, there are two types of symbols:

3. Comparison between FET and transistor

(1) FET is a voltage control element, while transistor is a current control element. When only a small amount of current is allowed to be taken from the signal source, the field effect transistor should be selected; When the signal voltage is low and more current is allowed from the signal source, transistors should be selected

(2) field effect transistor uses most carriers to conduct electricity, so it is called unipolar device, while transistor has both most carriers and a few carriers to conduct electricity. It is called bipolar device

(3) the source and drain of some FET can be used interchangeably, and the gate voltage can also be positive or negative, which is more flexible than transistors

(4) FET can work under the condition of very small current and low voltage, and its manufacturing process can easily integrate many FET on a silicon chip, so FET has been widely used in large-scale integrated circuits. (end)