How to identify the device by the labeling code on the IC component? What are the package types of SMD components?

Non-patch component electronic components can carry more production information, such as specification, model, manufacturer, and product serial number. The size or size of a patch element is measured in millimeters. There is not allowed to mark too much information on the body of the component. The identification method usually has:

1) Simplify the identification method. The conventional identification model is simplified, for example, 74LS14 (six inverter digital IC) is identified as LS14;

2) Code tagging, which further simplifies the identification, called code tagging. For example, the -24, 1L, etc. of the SMT transistors are more like passwords. It is necessary to use data to "decipher" them before they can know the meaning of the component specifications behind the logo.

3) No logo. Low-power (such as 16/1W) chip resistors, and (PF-level) small-capacity capacitors, because the device body is too small to print the logo, simply becomes a no-label component.

Beginners are often faced with such puzzling and very scratching questions: How do you identify the device by annotating code (also called printing) on ​​the IC component? How to find the relevant IC circuit data? How to determine the device without marking (printing) component, how to measure its quality? Can I replace the patch components with other types of components (even non-patch components)? What are the package types of SMD components? and many more.

Patch resistance

The chip resistor is a component with the largest number of applications on the circuit board. The shape is rectangular, black, and the resistance body is generally marked with white numerals (small resistors without labels, said no printed chip resistors), the inverter manufacturers in the circuit board The component serial number on the label is R (such as R1, R147, etc.). The basic parameters of the SMD resistors are nominal resistance, rated power, and error level. In addition to the maximum operating voltage and temperature coefficient, we only need to pay attention to the nominal resistance value and the rated power value.

Figure 1 SMD resistors

1, patch resistors operating parameters and categories

1) Rated resistance. The most common method is digital identification.

a, use 3 digital resistance values. The first two digits are ten digits and one digit value, which are valid numerical values. The third digit is the number of zeros or X power of ten. If labeled 152, that is 1500Ω; 101, that is, 100Ω; 103, that is, 10000Ω (10 kΩ).

The value below 1 Ω is denoted by R, such as 1R5, ie 1.5 Ω; R10, ie 0.01 Ω.

b. Use 4 digits to indicate the resistance value. The first 3 bits are valid values, ie, the thousands, one hundred, and one digit values, and the fourth digit is the number of zeros. For example, if the label is 1501, it is 1500Ω; the label is 1000, which is 100Ω; the label is 681, which is 680Ω; the label is 1003, which is 100kΩ. The value below 1Ω plus R is as above.

3 color ring and 4-color ring resistance value labeling method, not common, the labeling rule is the same as the ordinary resistance, and will not repeat them. The precision patch resistor is coded by the code labeling method, which consists of two digits and one code, the first two digits. For valid values, the third letter is the multiplier value. Such as 01A - 100Ω, 02 C - 100kΩ, not common, but must pay attention!

2) Rated power. Digitally-identified chip resistors are mostly black and their power levels are divided into 1/20W, 1/16W, 1/8W, 1/10W, 1/4W, 1/2W, 1W, etc. to 1/16W, 1/ The 8W, 1/10W, and 1/4W applications are the most common. The higher the general power, the larger the resistance volume, and the power level is gradually increasing with the size. In addition, the same shape, the darker the color, the greater the power value. Dissipation resistors with a power rating of 1W or more must not be in direct contact with the printed circuit board due to heat dissipation requirements. Therefore, the chip resistance used on all circuit boards is generally less than 1W. The power value of the patch resistor is limited, so in places where a large power resistor is needed in the circuit, multiple patch resistors are often connected in parallel (plus series) to increase the power value. The power value of the chip resistor is not directly marked on the resistor body, and the value of the resistor power value can be judged according to the “head” of the resistor.

When using resistance elements, look at the digitally labeled resistance values. Second, look at the size of the resistance. When the conditions are met, replace them.

3) Chip fuse resistance. This is a special type of chip resistors. For circuit safety reasons, it should not be replaced by ordinary chip resistors, or it can be easily shorted with a wire.

The chip fuse resistor is a special chip resistor that plays a fuse protection role in a circuit and is generally connected in series to a power supply branch of a unit circuit. When the current flowing through the resistor exceeds a certain value, the resistance thereof is The layer is quickly blown, cutting off the power supply of the circuit of the circuit, to avoid the increase of the fault. The digital signal of the resistor body is 000 or 0, which is the characteristic of the chip fuse resistance. The normal resistance value of the resistor is measured as 0Ω.

4) patch exclusion. This is another type of chip resistor, the most common being 4-pin 2-element patch, 8-pin 4-element patch, and 10-lead 8-element patch, 8 this 4-element patch The resistor has four independent resistance elements with the same resistance value, and the chip exclusion denoted as 472 means that the inner part contains four resistance elements with a resistance of 4.7k, which are used to concentrate the circuit using the same resistance element. The upper resistance of the MCU pin, for example, is more commonly used in the MCU interface circuit.

Figure 2 patch exclusion and internal equivalent circuit

2. How to determine the resistance and power of the SMD resistor?

If you can clearly see the digital sign on the chip resistor body, there is of course no problem in determining the resistance value and the power value. If the damaged resistor itself is not marked, or has been burned down beyond recognition, can not see the mark, then the resistance value of the replacement before the decision will take a little twists and turns, but also must be aware of in order to make the next repair. What methods can be used to make more accurate judgments?

1) Refer to the resistance of the corresponding element in the same circuit of this model. There are many identical circuits in the inverter circuit, such as 6 IGBT drive pulse transmission channels, of which 6 branches are exactly the same, from the MCU pulse signal output pin, to the buffer circuit, to the driver IC, to the IGBT gate, shot Polar circuit. Any one or several of the branches in the resistance or other components of the damage, may refer to the parameters of the patch components in the undamaged branch, if no identification, can be measured on the circuit board to determine or component soldered circuit board Determination. 3 phase output current (analog signal) transmission channel, 3 signal detection circuit is also generally the same, if there is damage to one way, may not damage the two components of the parameters to determine the parameters of damaged components.

As shown in Figure 2-9, the peripheral circuit components of PC5 and PC6 are identical. The peripheral components of PC3 and PC8 are the same. R17=R51, R23=R48, R22=R49... ..., When PC3 peripheral components are damaged or bad, you can "copy" the parameter values ​​of PC5 corresponding external components to repair.

In the same way, when the damage of other components, such as transistors, diodes, and IC chips, cannot be determined when parameters of the components are damaged, the replacement can be performed by referring to the parameter values ​​of the same type of circuit components.

2) Determine the component parameters according to the circuit type. If the pull-up and pull-down resistors connected to the MCU (microcontroller) pin are damaged, the MCU needs a digital port with external pull-up and pull-down resistors. Generally, the internal open-drain structure is used. Pull-up or pull-down resistors can be used to avoid I/O. The mouth has a level drift state, maintaining a statically stable level. The resistance selection value is generally 10kΩ, 6.8kΩ, 5.1kΩ, 4.7kΩ, 3.3kΩ, etc. If the value is too small, the power consumption increases. If the value is too large, level shift or interference is easily introduced. As long as it is determined that the damaged chip resistor is the upper and lower resistors of the MCU pin, it can be directly determined that the resistance of the damaged component is within the range of 3.3-10 kΩ. Of course, it is also possible to refer to the resistance values ​​of other upper and pull-down resistors.

Figure 3 refers to the schematic diagram of component parameters in the same circuit

Figure 4 Circuit diagram of the MCU pin pull-up resistor

As shown in Figure 4, the pull-up resistance of U2's pulse pin is 5.1k, which is in the range of 3.3~10kΩ.

3) Determine the component parameter values ​​with reference to similar models. The same circuit may not be referenced, nor can it roughly "evaluate" the parameters of the components as the pull-up and pull-down resistors do, and the same type of model may be compared for measurement, and the parameter values ​​of the damaged components may also be determined.

4) Adjust the test to get the parameter values ​​of the components. If there is no similar model for reference, it takes some effort to map out the part of the circuit, understand the location and specific role of the damage resistance in the circuit, and the connection method with other components, "estimate" the approximate resistance value, if not Grasp, will damage the resistance, temporarily access potentiometer, inverter power, adjust the potentiometer to test, with the artificial signal given, the subsequent circuit response to the signal, the panel display, etc., measure the resistance value of the potentiometer, and then Determine the parameters of the damaged resistor.

3, patch resistance measurement and appearance inspection

1) Measured online with a multimeter. When the resistance value is greater than the nominal value, it indicates that the component has a breaking fault or the resistance value has become larger and has been damaged; when the measured resistance value is less than the nominal value, it must be taken into account that the peripheral parallel component causes damage. The effect of this is that one or both ends of the component should be disconnected from the circuit and measured to obtain an accurate measurement.

2) The appearance characteristics of patch resistors are as follows:

a. The secondary vitreous protective film on the surface of the patch resistor should be well covered and come off, and may have been damaged;

b. The surface of the component should be flat. If some “bumps” are reproduced, it may be damaged.

c. The lead-out electrode of the component should generally be flat, with no pinholes and no discoloration. If cracks appear, it may be damaged.

d. The surface of the resistor body is black and may have been damaged;

e. The resistor body has been deformed and may be damaged.

4, replacement of chip resistors

Replacement of chip resistors, in addition to requiring the same resistance value, but also pay attention to the size and power value. Small signal circuits (such as MCU motherboard circuits) first require the same size for easy soldering installation. Substitution notes are as follows:

1) Strictly replace the original parameters. Analog signal processing circuits, such as proportional amplifier circuits, have strict values ​​for the input resistors and feedback resistors, and the resistance values ​​of the substitute components should be the same as those of the original damaged components. This does not allow the difference to be too large, otherwise it will cause circuit malfunctions.

2) For digital circuit components, such as the above connection, pull-up resistors, isolation resistors, etc., there is a certain range of values, as long as the signal voltage changes significantly, in line with the high and low level of the required range. First, the component substitution should be selected with the same parameters. If you can't find the same resistance component, you can replace it with a component that is close to the value. Generally, it will not affect the circuit performance. If the 4.7kΩ resistor is damaged, it can be replaced with a 5.1kΩ or 6.8kΩ resistor.

3) Non-patch components can be substituted. The damage rate of the chip resistor is extremely low, except that the drive circuit may be damaged due to the possibility of strong electric shock (parts of spare parts that can be purchased). The components of other circuits are rarely damaged, and there may be one or two damaged types. Unable to purchase spare parts. When such damaged components are encountered, using a non-patch 1/4W or 1/8W common resistor is not a problem. It is not the case that the original parts do not result in the maintenance progress. Of course, we must pay attention to welding, do the lead shaping, as long as possible to make the lead shorter, if necessary after welding 704 plastic coating reinforcement, can also achieve high-quality repair requirements.

Chip capacitors

Chip capacitor is a kind of component with a large number of applications on the circuit board. The shape is rectangular, yellow, cyan and cyan gray, and semi-transparent light yellow is common (it is a ceramic capacitor that is sintered at high temperature and cannot be printed. ). A small-capacity (skin-grade) capacitor is generally not marked on the capacitor body, and the micro-level capacitor has a mark (a few applications, a slightly larger capacitance, and a socket capacitor with a lead). The serial number of the component marked by the inverter manufacturer on the circuit board is C (such as C1, C47, etc.). Since the components of the actual circuit board of the inverter are installed compactly, the serial number is generally only indicated but the capacity value is not marked. The basic parameters of the chip capacitor include capacitance, operating voltage, leakage current, and error. The supply voltage for a small-signal circuit is generally 15 V or less. For example, the power supply for an MCU motherboard is 5 V. Therefore, in practical applications, only the first A parameter of capacitance and size (easy to install) is sufficient.

Fig. 5 Outline drawing of non-polar chip capacitor and tantalum capacitor element

SMD capacitors used in inverter circuits mainly include non-polar small-capacity chip capacitors (used for IC small-signal filtering, which suppresses ringing), and polar-polarity tantalum capacitors (a type of electrolytic capacitor used for power supplies). The output filter) is two kinds, the withstand voltage is below 63V. Capacity in the 10 microFarad and high voltage capacitors, often using ordinary capacitors.

1, no identification chip capacitor capacity estimation, detection and substitution

1) SMD capacitors for the power supply output of the switching power supply circuit and the power supply input of the IC circuit. See the figure on the left side of the circuit in the figure above.

At the power supply output, it is connected in parallel with the (filtered) electrolytic capacitor. Due to the electrolytic capacitor-based lead plate and the insulating medium wound together, it has an "inductive effect" and the high-frequency filtering effect is poor. Parallel small-capacity capacitors filter out the rectified high-frequency ripple components. The power supply terminals of ICs in the circuit are also provided with high-frequency filter capacitors to absorb power disturbances (which may be caused by parasitic inductance formed by the leads or caused by some kind of interference). The capacitance of such capacitors is generally about 0.01~0.1μF. This type of capacitor does not require strict capacity and the failure rate is relatively low. If it is found to be damaged, it can be replaced with a capacitor in the range of 0.01 to 0.1 μF.

2) SMD capacitors used for low-pass filters in the signal path. A low-pass filter circuit is used to attenuate and absorb high frequency components in a certain frequency band in a signal, and requires only low frequency components (even direct current components) in the signal to pass through. In the signal transmission path of the inverter, it is mostly used to convert the pulsating DC signal into a DC signal through an RC circuit, so the capacitance in this circuit is approximately 0.01 to 0.47 μF, because of the effect of the resistor R, although the capacitance is small, RC total time constant is not small, can also achieve better filtering results. If it is not possible to confirm the size of the capacitor, a capacitance test of 0.01 to 0.47 μF in terms of content may be used. It is preferable that the pulsed component is not filtered after RC filtering.

3) Chip capacitors with a specific capacity. For example, the compensation capacitance of the MCU crystal pin is related to the MCU type and the crystal frequency. The capacity of the capacitor can be determined by the relevant data of the MCU and the frequency of the crystal element labeled, typically 33PF or 22PF, 15PF.

Chip capacitor damage and detection methods:

a, the same type of capacitor, the larger the head or the darker the color, the larger the capacity. The capacity of the capacitor can be measured with a dedicated capacitance tester. Some digital multimeters currently have this feature. When measuring the capacitance, the chip capacitor must be disconnected at least at one end, and after the influence of the external circuit is excluded, the detection is performed again.

b. Test with a multimeter. If it is detected online, the multimeter measures the resistance value between the two pins of the capacitor. It is actually the “integral resistance value” of the external circuit connected to the capacitor. If the capacitor is short-circuited or near-short-circuited (very low resistance value) Can be reflected. Remove the capacitor from the original circuit and measure its resistance to infinity. When measuring with the x10k block of the pointer table, the capacitance pointer of about 0.1 μF has a jumping (charging) phenomenon, and it returns to infinity after being stopped. If a fixed resistance value is measured, the capacitor is damaged.

c. Power-on detection. The circuit judges the voltage drop at this point, which may be caused by the leakage of the capacitor. See the circuit example below. This is also a better way.

As shown in Figure 6 below, the normal value of the measured voltage at point a should be the voltage division value of R221 and R22 to 3V power supply. If the measured voltage value is higher than 1.5V, it may be caused by the leakage of capacitor C112; The normal value of the voltage should be 3V. If it is lower than 3V, it may be caused by the leakage of the capacitor C56.

Figure 6 Voltage leakage causes voltage drop at point A

Further, the C112 or C56 solder-off circuit can be verified by measuring its pin resistance.

When the chip capacitor is damaged, as well as the resistance value of the chip resistor, the same circuit can be used to determine the capacitance of a good capacitor element to determine the fault capacitor parameters. If the pin capacitance of the crystal oscillator is broken, measure the capacitance of the capacitor element of the other pin. The capacity of the two capacitors is the same.

Replacement of faulty capacitors: The failure rate of chip capacitors is relatively low, and patch capacitors of various sizes must be spare parts, which is obviously not realistic. Occasionally, when damage is found, it is entirely possible to replace it with an ordinary ceramic capacitor or Jawlon capacitor. Note that the lead should be as short as possible and the welding quality should be better.

2. Capacity identification, detection and substitution of polar (labeled) patch capacitors

The shape of a polar patch capacitor is shown in the right component diagram in Figure 2-11. There are generally two types of rectangular patches and cylindrical patches. The shape and shape of the latter are similar to ordinary capacitors and they are easy to identify. Discuss it. The color of a rectangular patch capacitor is mostly silver or black, and one end marked with a crossbar is positive (this can be further judged by the way it is connected in the circuit - one end of the crossbar is connected to the positive terminal of the power supply). According to the different package types, the breakdown voltage is divided into four grades: A (10V), B (16V), C (25V), and D (35V), and the capacity is mostly from several microfarads to several tens of microfarads.

The specifications of the chip capacitor include parameters such as capacitance, rated voltage, capacity error, size, and package type. There are differences among different manufacturers. It is very difficult (and unnecessary) to remember or understand.

Examples of labels with polar capacitors:

1) Using the digital annotation method, using a letter + 3 digits, such as A475, the first two digits in the figure are valid values, and the last digit is zero, that is, 4700000PF=4.7μF. A is a pressure rating, 10V.

2) Direct tagging. Such as 16V 10, that is 10μF, voltage 16V with a polar capacitor.

3) Four-color ring labeling method. The color and number of the color ring corresponding relationship, brown (or brown) 1, red 2, orange (or orange) 3, yellow 4, green 5, blue 6, purple 7, gray 8, white 9, black 0, with the ordinary The color circle of resistors is the same. (From left to right) The first two color rings are valid, the third color ring is zero, and the fourth color ring is rated voltage. Such as yellow, green, green, the first 3 rings for the 4700000PF (4.7μF), the fourth color ring indicates the rated voltage of 10V.

4) The code marking method is difficult to identify without relevant data. According to the code, according to the data "translation" out of the capacitor capacity and pressure and other parameters.

For the determination of fault capacitor parameters, assuming that it is difficult to determine from the identification, the other methods such as the determination of the chip resistance mentioned above can also be used to determine and determine the parameters of the components. For example, the same can be found in the circuit. The labeled chip capacitor uses the capacitance meter to measure the same capacitor and can determine the capacitance. If the voltage is higher than the power supply, it can be used. For example, if the power supply is 5V, you can use 6.3~16V.

There is a good or bad judgment of the polar patch capacitor:

Chip capacitors have breakdown short circuit, internal electrode open circuit, leakage, capacity reduction and other failures, detection methods common electrolytic capacitor detection and judgment methods. Using a digital multimeter to measure the capacitance, or the resistance of an analog multimeter to measure charge and discharge and the static resistance, can determine the quality of the capacitor.

Patch replacement with polar capacitors:

1) If it is easy to purchase the “original parts” of the original model and original package, the substitution is most convenient. The source of the original parts is generally two: procurement, from the (electronic components mall) suppliers, or from (Dangdang.com, Taobao can be used to buy the original parts of the original accessories used network); scrap circuit board demolition. No matter where you get the accessories, you must first measure, determine is good, and then welding to the circuit board, there must be a "measurement verification" before welding this link, to avoid detecting a bad component, and then put on a bad Components, so that the repair into the wrong area lead to the phenomenon of repair failure.

2) The damage rate of the patch with polar capacitors is also quite low. If the installation space permits, it is not a problem to use an ordinary electrolytic capacitor with the same capacity and withstand voltage to meet the requirements. Pay attention to the use of electrolytic capacitors with good quality (small temperature coefficient, stable performance), and the welding pin should be short. After the use of 704 rubber reinforcement.

Chip inductors

The number of applications of SMD inductors in the circuit is small. Only at the output of the low voltage DC control power supply, see its application, and the filter capacitor forms the π-shaped filter circuit of the CLC. It has the effect of stabilizing the output current by suppressing the sudden change of current. . Inductive components consist of single coils, some with magnetic cores (large inductances), and units generally denoted by μH and mH, and currents in the range of a few milliamperes to several hundred milliamperes.

SMD inductors are available in round, square, and rectangular packages and are mostly black in color. With iron core inductance (or circular inductor), easy to identify from the appearance. However, some rectangular inductors look more like chip resistors. The label of the inductor of the inverter manufacturer on the circuit board is marked with "L". Inductor operating parameters are inductance, Q (quality factor), DC resistance, rated current, self-resonant frequency, etc., but patch capacitance is limited by the size of the sensor, most of them only indicate the inductance, other parameters are not marked, and often are The indirect labeling method—labeled on the body of the chip inductor, is only part of the information of the entire specification and model, that is, most of them are only inductance information.

Figure 7 SMD inductor outline

SMD inductor tagging example: Actual (printing) labeling - 101, complete model - MPI 0610 MT 101 (including type, size, error, package type, inductance, etc.), is a chip inductor with an inductance of 100μH . 1R1 is a chip inductor with an inductance of 1.1μH. Some use one letter to represent the inductance (code markup method), the actual labeling - E, the complete model - MPE0312NT2R7, is a chip inductor with an inductance of 2.7μH.

SMD inductor identification method:

1) From the exterior, such as a square or round inductor with magnetic core, the volume is slightly larger and the magnetic core and coil can be seen;

2) Some SMD inductors are the same as the SMD resistors in appearance, but they are not marked with numbers and letters. There is only a small circle marked, meaning an inductive component;

3) The serial number of the component in the circuit is often marked as L, such as "L1", "DL1", etc.

4) There is an inductance mark, such as 100.

5) The AC resistance of the ideal inductor is large, and the DC resistance is zero. The measured value of the inductive element is extremely small, and the resistance is close to zero ohms. From items 3), 4), and 5), with observations and measurements (positions and effects in the circuit), it can be distinguished whether the component is a chip resistor or a chip inductor, and the inductance component is determined.

6) Use a dedicated inductance tester to disconnect the circuit from the device and measure its inductance.

The quality of chip inductors:

1) First determine the inductance element;

2) Observe the appearance of deformation, discoloration, disintegration, etc. If the above phenomenon, may have been damaged;

3) Use the multimeter's small blocking position (such as 200 or 1 block) and measure the DC resistance to be close to 0. If the measured resistance value is large or infinite, the inductor element is damaged.

Fault replacement of chip inductors:

1) Can replace the same type of component replacement from the old circuit board;

2) First determine the inductance and current value, replace it with a normal lead-inductor, and fix it;

3) Self-winding, making inductive alternatives, with a certain degree of difficulty;

4) If there is no obvious effect on the circuit performance, the emergency repair can be temporarily shorted (for reference only, this repair method is not recommended and may reduce some of the product's performance).