Component procurement essential basic knowledge book

As an electronic components procurement, not only do you need flexible business skills, you also need to master the classification of electronic components, model identification, usage and other professional basic knowledge in order to provide more professional procurement advice to enterprises.
Classification of electronic components
The basic parts used to manufacture or assemble the electronic machine are called electronic components, and the components are the independent individuals in the electronic circuit.
Active and Passive Components
Active components refer to components that can excite active functions such as amplification of electrical signals, oscillation, control of current or energy distribution, and even perform data operations and processing when energy supply is obtained.
Active components include a wide variety of transistors, integrated circuits (ic), video tubes, and displays.
Passive components relative to active components are those that cannot excite amplification, oscillation, etc., of electrical signals, and the response to electrical signals is passive and submissive, while the electrical signals pass through the electronic components according to the original basic characteristics.
The most common resistors, capacitors, inductors, etc. are passive components. Active and passive components
Active components correspond to active components. If an electronic component works with the presence of a power source inside it, this device is called an active component and requires a source of energy to achieve its specific function.
Active devices themselves also consume power, and high-power active devices are usually equipped with heat sinks.
The opposite of passive components are passive components. Resistors, capacitors and inductors are called passive components because they can perform their prescribed functions without the need for an external excitation power supply when a signal is passed through the circuit.
Passive devices consume little electrical energy themselves, or convert electrical energy into other forms of energy.
Discrete components are the same as integrated circuits (ic)
In terms of physical structure, circuit function and engineering parameters, active devices can be divided into two categories: discrete components and integrated circuits. Discrete components are opposed to integrated circuits (ic).
Integrated circuit (ic integrated circuit) is a kind of circuit required in a class of transistors, resistive and capacitive components and wiring interconnected together, made in a small piece or several small pieces of semiconductor wafers or dielectric substrates, packaged as a whole, with the circuit function of electronic components.
Discrete components are ordinary resistors, capacitors, transistors and other individual electronic components, collectively referred to as discrete components. Discrete components are single-function, "minimum" components, no longer have other components inside the functional unit.
Distinction between circuit-type components and connection-type components
Passive devices in electronic systems can be divided into circuit-type devices and connection-type devices according to the circuit function they perform.
Distinction between circuit-type components and connection-type components
Identification of common electronic components

I. Resistance
Resistors, as we are accustomed to call them, are the most commonly used electronic components in electronic equipment, and are represented by "r" plus a number in the circuit, e.g., r13 means the number 13 resistor. The main role of resistors in the circuit is shunt, current limiting, voltage dividing, biasing, filtering (used in combination with capacitors) and impedance matching.
Parameter identification: the unit of resistance is ohm (ω), multiplier units are: kilo-ohm (kω), megohm (mω), etc. Conversion method is: 1 megohm (mω) = 1000 kilohm (kω) = 1000000 ohms
There are three methods of labeling the parameters of resistance, namely, the direct scale method, the color scale method and the number scale method.
1, the number of marker method is mainly used for SMD and other small volume of the circuit, such as: 472 said 47 × 100ω = that 4.7k; 103 said 10000ω (10 followed by three 0) that is, 10kω
2, the color ring labeling method is most used, the first color ring indicates the maximum resistance of a number, the second color ring indicates the second number, the third color ring indicates the resistance should not have several zeroes, the fourth color ring indicates the error of the resistance value.
Color ring labeling method
The relationship between the color scale position and the multiplier of the resistor is shown in the following table.
Relationship between color scale position and multiplicity of resistance

II. Capacitance
Capacitor is a component made up of two metal films close together and separated by an insulating material in the middle. Capacitance in the circuit is generally expressed by "c" plus a number, such as c223 indicates the number 223 capacitor capacitance characteristics are mainly isolated direct flow AC.
There are also two main parameters of the capacitor, the nominal capacity and the allowable error.
1, nominal capacity, refers to the capacitor capacity marked on the capacitor, the size of the capacitor capacity is to indicate the size of the electrical energy can be stored, the capacitor on the AC signal obstruction is called capacitive resistance, it is related to the frequency and capacity of the AC signal.
Capacitive resistance xc = 1/2πf c (f denotes the frequency of the AC signal, c denotes the capacitance capacity)
Identification method: The identification method of capacitance is basically the same as that of resistance, and it is also divided into three kinds of direct scale method, color scale method and number scale method. The basic unit of capacitance is expressed in farad (f), other units are: millifarad (mf), microfarad (uf), nanofarad (nf), picofarad (pf). Where: 1 farad = 103 millifa = 106 microfa = 109 nanofa = 1012 picofar
Direct marking method: The capacity value of capacitor with large capacity is marked directly on the capacitor, such as 2200 uf/10v
Alphabetical representation: 152m=1500pf
Digital representation: Generally, three digits are used to indicate the size of the capacity, the first two digits indicate the effective number, and the third digit is the multiplier. For example: 102 means 10×102pf=1000pf
2、The allowable error is divided into three levels, the same as the resistor error indication. The trimmer capacitor and variable capacitor are marked with the minimum and maximum values of its capacity, such as 7/270p

III. Inductance
The inductance coil is made by winding the insulated wire around a certain number of turns on an insulated skeleton. DC can be passed 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, the coil ends will produce self-induced electromotive force, the direction of self-induced electromotive force and the direction of the applied voltage is opposite to prevent the passage of AC, so the characteristics of the inductor is through DC resistance AC, the higher the frequency, the greater the coil impedance. The higher the frequency, the higher the impedance of the coil. Inductors can be used in circuits with capacitors to form oscillating circuits.
Inductance in the circuit is often expressed as "l" plus a number, for example: l3 indicates the inductance numbered 3.
Inductance generally has a straight scale method and color-coded method, color-coded method is similar to the resistance. The basic unit of inductance is: Hen (h) Conversion units are: 1h = 103mh = 106uh.

IV. Crystal diodes
The main characteristic of diodes is unidirectional conductivity, that is, under the action of forward voltage, the on-resistance is very small; and under the action of reverse voltage on-resistance is very large or infinite. Crystal diodes in the radio for radio wave detection, in the power conversion circuit to AC into pulsating DC, in the digital circuit as a non-contact switch, etc., are the use of its one-way conductive properties.
Crystal diodes can be divided into: rectifier diodes (such as 1n4004), isolation diodes (such as 1n4148), Schottky diodes (such as bat85), light emitting diodes, voltage regulator diodes, etc. according to their role.
1, identification method: the identification of the diode is very simple, the n-pole of the low-power diode (negative), in most of the diode appearance using a color circle marked out, some diodes also use the diode special symbol to indicate the p-pole (positive) or n-pole (negative), there are also symbols marked as "p", " n" to determine the polarity of the diode. The positive and negative polarity of light-emitting diodes can be identified from the length of the pin, the long leg is positive, the short leg is negative.
2、Main parameters
The rated forward operating current is the maximum forward current value allowed to pass through the diode during long-term continuous operation. Because the current through the tube will make the core heat up, the temperature rises, the temperature exceeds the permissible limit (about 140 for silicon tubes, about 90 for germanium tubes), it will make the core overheat and damage.
The maximum reverse operating voltage, the reverse voltage added to both ends of the diode is high to a certain value, the tube will break through and lose its one-way conductivity. In order to ensure the safety of use, the maximum reverse working voltage value is specified.
Reverse current is the reverse current flowing through the diode under the action of the specified temperature and maximum reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the tube. It is worth noting that the reverse current has a close relationship with the temperature, about 10 for every increase in temperature, the reverse current doubled.

V. Crystal Triode
Crystal transistors have an amplifying and switching role in circuits. We use crystal transistors to amplify weak signal currents in circuits or to make automatic switches to control the on/off of appliances. Crystal transistors in the circuit is often indicated by "q" plus a number, such as: q1 means the number of 1 transistor.
Commonly used crystal transistor package form of metal package and plastic package 2 major categories, the pin arrangement with a certain pattern. The three poles of the crystal transistor are called the base (b), collector (c) and emitter (e), and the arrow on the emitter indicates the direction of current flowing through the transistor.

VI. Integrated Circuits
Integrated circuit is a diode, transistor and resistor-capacitor components in accordance with the requirements of the circuit structure, made on a small piece of semiconductor material to form a complete circuit with certain functions, and then packaged, its literal symbol is ic.
Integrated circuits are the late 60s, with the development of electronics technology and the rapid development of. The use of integrated circuits and the use of discrete components to assemble the circuit, with fewer components, light weight, small size, good performance and power saving and many other advantages, so the integration of electronic products has become an inevitable trend in the development of electronic technology.

Distinguish between original and bulk new ic chips
There are many different kinds of ic chips on the market, so if you don't pay attention to the distinction, it is sometimes difficult to see the difference between various materials. Now let's see what are the key points to distinguish the original from the new chips.

Distinguish between original and bulk new ic chips
1 Look at the surface of the chip whether there are polished traces
Where the surface of the polished chip will have fine lines and even microscopic traces of the previous printing, some to cover up also coated with a thin layer of paint on the surface of the chip, looks a little shiny, no plastic texture.
2 Look at the print
Nowadays, most of the chips are laser marked or printed with a special chip printer, with clear handwriting, neither conspicuous, not blurred and difficult to erase. Refurbished chips either have a "jagged" sense of cleaning agent corrosion along the edge of the handwriting, or the print is blurred, varying depths, incorrect location, easy to erase or too conspicuous.
Silk-screen printing process has now been eliminated by the big ic manufacturers, but many chip refurbishment due to cost reasons still use silk-screen printing process, which is also one of the basis for judgment, silk-screened words will be slightly higher than the surface of the chip, with the hand can feel the slightest uneven or astringent feeling. However, recently the phenomenon of using laser marking machine to modify the chip mark more and more, especially in the memory and some high-end chips, once the location of the laser printed word there are individual letters uneven, uneven thickness of the strokes, can be identified as refurbished.
The main method is to look at the overall coordination, the handwriting and background, the degree of newness of the pins do not match the word mark such as too new, too clear there is a greater possibility of problems, but many small factories, especially some small domestic ic company's chips are born so, which adds a lot of trouble for the identification, but the judgment of the mainstream of large manufacturers of chips this method is still very meaningful.
3 Look at the pins
Where bright as "new" tin-plated pins must be refurbished goods, the vast majority of genuine goods ic pins should be the so-called "silver powder feet", darker but uniform color, the surface should not be oxidation traces or "flux", in addition dip and other plug-in pins should not be scuffed traces, even if there is (again packaging will have) scuff marks should also be neat, the same direction and metal exposure at the clean without oxidation.
4 Look at the device production date and packaging factory label number
The markings of genuine goods including the markings on the bottom of the chip should be consistent and the production time is consistent with the device phase, while the markings of un-remarked refurbished chips are confusing and the production time is not the same. If the label number on the bottom of the device is confusing, it also means that the device is remarked.
5 Measure the thickness of the device and look at the edge of the device
Many of the original laser printing polished refurbished piece (power devices mostly) because to remove the original mark, must be polished deeper, so the overall thickness of the device will be significantly smaller than the normal size, but not compared or measured with calipers, the general inexperienced people are still difficult to distinguish, but there is a workaround to recognize the law, that is, look at the front edge of the device.
Because the plastic sealing device injection molding must be "off the mold", so the device edge corner is rounded (r angle), but the size is not large, grinding processing is easy to grind this rounded corner into a right angle, so the front edge of the device once the right angle, can be judged as polished goods.
6 Look at the packaging
In addition, another method is to see whether the business has a large number of the original outer packaging, including the logo inside and outside the same carton, anti-static plastic bags, etc., the actual identification should be used in a number of ways, there is a problem can be identified as the quality of the goods of the device.

Summary
In addition to these basic component knowledge, procurement personnel still have a variety of business skills to understand the market situation and explore supply channels. To combine offline market visits and online trading platform, in order to ensure the procurement of genuine components at affordable prices and high quality for enterprises.