As a purchaser of electronic components, it is necessary not only to have flexible business capabilities, but also to master basic professional knowledge of electronic components classification, model identification and usage, so as to provide more professional procurement suggestions for enterprises.

Classification of electronic components

The basic parts used for manufacturing or assembling electronic whole machine are called electronic components, components are independent individuals in electronic circuits.

Active and passive components

Active component refers to the component that can activate the active functions such as signal amplification, oscillation, control current or energy distribution and even perform data operation and processing when energy supply is obtained.

Active components include various transistors, integrated circuits (ICS), image tubes and displays.

The passive component relative to the active component, refers to the electric signal can not be excited amplification, oscillation, etc., the response to the electric signal is passive and obedient, and the electric signal according to the original basic characteristics through the electronic component.

The most common resistors, capacitors and inductors are passive components.

Active and passive components

What is the basic knowledge of electronic component purchasing

The active component corresponds to the active component. If an electronic component is operating with an internal power source, it is called an active device and requires a source of energy to perform its specific function.

Active devices also consume power themselves, and high power active devices usually have heat sinks.

The counterpart of the passive element is the passive element. Resistance, capacitance and inductance components in the circuit through the signal can complete the specified function, do not need to add an incentive power supply, so called passive components.

Passive devices consume very little energy of their own or convert it to a different form of other energy.

Discrete components are related to integrated circuits (ICS)

In terms of physical structure, circuit function and engineering parameters, active devices can be divided into discrete devices and integrated circuits. Discrete components are as opposed to integrated circuits (ics).

IC Integrated circuit (IC Integrated Circuit) is an electronic component with circuit function that interconnects transistors, resistive and capacitive components and wiring, and makes them into a small piece or several small pieces of semiconductor chip or dielectric substrate.

Discrete components refer to ordinary resistance, capacitance, transistor and other single electronic components, collectively known as discrete components. A discrete component is a single, “minimal” component with no other functional unit inside.

Circuit type components are distinguished from connection type components

Passive devices in electronic systems can be divided into circuit devices and connection devices according to their functions.

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Identification of common electronic components

A, resistance
Resistors are commonly called resistors and are the most commonly used electronic components in electronic equipment. Resistance is represented by “R” plus numbers in the circuit. For example, R13 represents the resistance numbered 13. The main functions of resistors in circuits are shunt, current limiting, voltage divider, bias, filter (used in combination with capacitors) and impedance matching.

Parameter identification: the unit of resistance is ohm (ω), the unit of multiplier is: thousand ohms (K ω), megohm (mω) and so on. The conversion method is: 1 megohm (mω) =1000 kilohm (K ω) = 1,000,000 ohms

What is the basic knowledge of electronic component purchasing

There are three methods to mark the parameters of resistors, namely, direct label, color label and number label.

1, number standard method is mainly used for patches and other small volume circuit, such as: 472 47×100ω= that is 4.7K; 103 is 10,000 ω (10 followed by three zeros), which is 10kω

2, color ring labeling method is the most used, the first color ring represents the resistance value of the largest number, the second color ring represents the second number, the third color ring represents the resistance value should not have several zeros, the fourth color ring represents the resistance value error.

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The relationship between the color code position and the rate of resistance is shown in the following table:

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Second, the capacitance

Capacitance consists of two metal films close together, separated by an insulating material. Capacitors in the circuit generally use “C” plus a number, such as C223 indicates the number of the capacitor 223 capacitors are mainly separated direct current AC.

Capacitors also have two main parameters, nominal capacitance and allowable error.

1, nominal capacitance, refers to the capacitance marked on the capacitor, capacitance capacity is the size of the storage of electric energy, capacitance to the AC signal blocking effect is called capacitive reactance, it is related to the frequency and capacitance of the AC signal.

Capacitive reactance xc = 1/2 PI c f

(F represents the frequency of the AC signal and C represents the capacitance)

Identification method: the identification method of capacitance and resistance is basically the same, also divided into direct standard method, color standard method and numerical standard method. The basic unit of capacitance is expressed in Farad (f), and other units are: millimeter (MF), micrometer (UF), nano method (NF), and skin method (PF). Where: 1 farad =103 millifa =106 microfa =109 nanfa =1012 picofa

Direct label method: the capacity value of the capacitor with large capacity is directly indicated on the capacitor, such as 2200 uF / 10V

Letter notation: 152m=1500pf

Numerical representation: the capacity is usually represented by three digits, the first two digits represent significant digits, and the third digit is the multiplier. For example, 102 indicates that 10 x 102PF = 1000PF

2. The allowable error is divided into three levels, the same as the representation of the resistor error. Trimmer and variable capacitors indicate their minimum and maximum capacitance, e.g. 7/270p

Third, inductance

Inductance coil is made by winding an insulated wire around an insulated skeleton a certain number of times. Dc can pass through the coil, dc resistance is the resistance of the wire itself, the voltage drop is very small; When the AC signal through the coil, both ends of the coil will produce self-induced electromotive force, the direction of the self-induced electromotive force and the direction of the applied voltage is opposite, blocking the AC through, so the characteristics of inductance is dc resistance AC, the higher the frequency, the greater the coil impedance. Inductance and capacitance can form an oscillating circuit in a circuit.

Inductance in the circuit is usually “L” plus numbers, such as: L3 refers to the inductance number 3.

Inductance generally has the direct standard method and the color standard method, the color standard method is similar to the resistance. The basic unit of inductance is: H (h) conversion unit: 1H = 103MH =106uh.

Four, crystal diode

The main characteristic of diode is unidirectional conductivity, that is, under the action of forward voltage, the conduction resistance is very small; Under the action of reverse voltage, the conduction resistance is extremely large or infinite. Crystal diode is used to detect radio waves in radio, to transform alternating current into pulsating direct current in power conversion circuit, and to act as a contactless switch in digital circuit.

According to the role of crystal diode can be divided into: rectifier diode (such as 1N4004), isolation diode (such as 1N4148), schottky diode (such as BAT85), light emitting diode, voltage regulator diode, etc..

1, the identification method: identification of a diode is very simple, small power diode n pole (cathode), the diode looks mostly USES 1 kind of color ring marking out, some diodes also use special symbols to represent a p (positive) or n (cathode), also have use symbols for “p”, “n” to determine of polarity of the diode. The positive and negative poles of leds can be identified by the length of the pins, with long pins being positive and short pins being negative.

2. Main parameters

Rated forward operating current refers to the maximum forward current allowed to pass through the diode during long-term continuous operation. Because the current through the tube will make the tube core heat, temperature rise, temperature exceeds the allowable limit (silicon tube is about 140, germanium tube is about 90), will make the tube core overheating and damage.

The highest reverse working voltage, when the reverse voltage at both ends of the diode is high to a certain value, the tube will break down and lose the one-way conductivity. In order to ensure safe use, the maximum reverse working voltage value is specified.

Reverse current refers to the reverse current flowing through the diode at the specified temperature and the highest reverse voltage. The smaller the reverse current, the better the one-way guide electrical performance of the tube. It is worth noting that the reverse current has a close relationship with temperature, approximately doubling for every 10 increase in temperature.

Five, crystal triode

The crystal triode has the function of amplifying and switching in the circuit. We use crystal triodes to amplify weak signal currents in circuits or to make automatic switches to control the on-off of electrical appliances. Crystal triode is commonly used in the circuit “Q” plus numbers, such as: Q1 stands for the number of 1 triode.

Commonly used crystal triode packaging forms are metal packaging and plastic packaging two categories, pin arrangement has a certain rule. The three poles of a crystal triode are called base (B), collector (C) and emitter (e). The arrow on the emitter indicates the direction of current flowing through the triode.

Integrated circuits

Integrated circuit is the diode, audion and resistor capacitor components in accordance with the requirements of the circuit structure, made on a small piece of semiconductor material, forming a complete circuit with a certain function, and then packaged, its character symbol is IC.

Integrated circuit is the late 60’s, with the development of electronic technology and rapid development. Compared with the circuit assembled by discrete components, the integrated circuit has many advantages such as fewer components, light weight, small size, good performance and energy saving, so the integration of electronic products has become the inevitable trend of the development of electronic technology.

Distinguish original and loose new IC chip

IC chips on the market, all kinds of, do not pay attention to distinguish, sometimes it is difficult to see how different various materials. Now let’s take a look at what separates the original chip from the new one.

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1, see whether the chip surface has polished traces

Every polished chip surface will have fine lines and even before printing micro marks, some to cover the chip surface is also coated with a thin layer of paint, looks a little shiny, plastic-free texture.

2, look at the printing

The vast majority of today’s chips use laser marking or a dedicated chip printer to print the word, which is clear, inconspicuous, not blurred and difficult to erase. The new chips either had “jagged” edges corroded by cleaning agents, blurred, different shades, poorly positioned, easily erased, or were too conspicuous.

Screen printing process is now IC factory has long been eliminated, but many chip renovation due to cost reasons still use screen printing process, which is one of the basis for judgment, screen printing words will be slightly higher than the chip surface, touch with the hand can feel the subtle uneven or astringent feeling. However, recently with the laser marking machine to modify the phenomenon of chip marking more and more, especially in memory and some high-end chips, once found that the location of the laser printing individual letters are not even, uneven stroke thickness, can be identified as refurbished.

Main method is to look at the overall coordination, handwriting is not in conformity with the background, pin condition such as the word mark about the possibility of new, there is something wrong with the qing dynasty is bigger also, but many small factory especially some domestic small chip IC company is born this way, it added a lot of trouble for identification, but the mainstream companies chip the judgment of this method is very meaningful.

3. Look at the pins

Where bright as “new” tin pins will be refurbished goods, the vast majority of IC pins should be so-called “silver powder feet”, dark color but uniform color, the surface should not have oxidation traces or “flux”, in addition to dip and other plug-in pins should not erase traces, Even if there is (repackaging will have) scratches should be neat, in the same direction and the metal exposure is smooth without oxidation.

4, look at the device production date and sealing factory label

The label of the original product, including the label of the bottom of the chip, should be consistent and the production time should be consistent with the product of the device, while the label of the refurbished chip without remark is confused and the production time is different. Although the label on the front of the chip is the same as that on the other side, sometimes the value is not reasonable (such as “lucky number”) or the production date is not consistent with the product of the device. If the label on the bottom of the device is confused, it also indicates that the device is made of remark.

5, measure device thickness and look at the edge of the device

Many original laser printing polishing refurbished pieces (mostly power devices) due to the removal of the original mark, must be polished deep, so the overall thickness of the device will be significantly less than the normal size, but not compared or measured with calipers, generally inexperienced people are still difficult to distinguish, but there is a flexible detection method, that is, to see the front edge of the device.

Because the plastic sealing device must be “moulded” after injection molding, the edge Angle of the device is round (R Angle), but the size is not large, and it is easy to grind the rounded Angle into a right Angle during grinding. Therefore, once the front edge of the device is a right Angle, it can be judged as polished goods.

6. Look at the package

In addition, another method is to see whether the business has a large number of original packaging, including the identification of the same inside and outside of the carton, anti-static plastic bags, etc., the actual identification should be more than the method used, there is a problem can identify the quality of the device.

In addition to the basic knowledge of components, the procurement staff is also equipped with diversified business capabilities, understanding market conditions and exploring supply channels. Offline market visits and online trading platforms should be combined to ensure that enterprises can purchase genuine components with fair price and high quality.

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