Basic knowledge of common electronic components

1. Resistor (R)
Resistor for short, refers to a component with certain technical performance that acts as a resistor in a circuit, which can be used to adjust the current and voltage in the circuit, or as a load in the circuit.
1. Parameters of resistance:
a. Resistance: refers to the value of the resistance. 0Ω—hundreds of MΩ
b. Dissipated power: refers to the maximum power that the resistor can withstand (consume) when it works for a long time.
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electric components
2. Resistor material:
Commonly used materials for resistors are carbon film, metal film, metal oxide film, wire wound, cement (ceramic) wire wound semiconductor and other materials.
3. Types of resistors:
Fixed resistance: refers to a resistance with a fixed resistance value
Fine-tuning resistor: refers to the resistor whose resistance value can be fine-tuned
Adjustable resistance: commonly known as potentiometer, refers to a resistance whose resistance value is continuously adjustable
Thermistor: refers to a resistor whose resistance value changes with temperature
a. Positive temperature coefficient thermistor: refers to the resistance (PTC) whose resistance value increases with the increase of temperature
b. Negative temperature coefficient thermistor: refers to the resistance whose resistance value decreases with the increase of temperature
Varistor: Refers to a resistor whose resistance value changes as the voltage changes.
Humidity resistance: refers to the resistance whose resistance value changes with temperature change
Photoresistor: refers to a resistor whose resistance value changes with temperature
Power representation of resistors: Generally, high-power (above 3W) resistors are marked with their power values ​​on the resistance shell, such as: 3W, 5W, 7W, 10W, 20W, 30W, etc., while low-power (below 3W) is partially marked with power , (such as: 3W, 2W, 1W, etc.), the ones that do not indicate the power are mostly low-power resistors with a power of less than 1W. For actual use, a resistor with a large power can be used to replace a resistor with a small power, otherwise it cannot be replaced. If When the size of the resistor power is not known, the resistor with the same or slightly larger volume can be used instead in practical applications.
5. Representation method of resistance value:
Directly indicate the value and unit of the resistance, such as: 1.5Ω, 160Ω, 1Ω, etc.
Directly indicate the value of the resistance and omit the unit “Ω”, such as: 100 is 100Ω, 1 is 1Ω, 22M is 22MΩ.
Use several X to represent several Ω, such as: 4Ω7, 9Ω1 is 9.1Ω, 8M2 is 8.2MΩ, etc.
Some use several R to represent several Ω, such as: 1R5 is 1.5Ω, 3R9 is 3.9Ω, etc.
The resistance value is followed by other English letters (such as: J, K, M, etc.) or Roman numerals (Ⅰ, Ⅱ, Ⅲ) or positive and negative percentages (such as: ±5%, ±10%, ±20%). It indicates the error level of the resistor.
Digital representation method (chip resistors and some trimmer resistors and potentiometers use this method)
It is represented by three digits, the first and second digits represent the significand, and the third digit represents the multiplier (1 is 101, 2 is 102, 3 is 103, 4 is 104, … 8 is 108, but 9 is 100 ) Multiply the effective number by the multiplier, that is, the resistance value. (unit: Ω)
Color circle notation:
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6. Color ring resistance
The resistance that uses the color circle to represent the resistance and the error is called the color circle resistance
Four-color ring resistor (for ordinary resistors, the most used)
The first and second color circles indicate the significant number, the third color circle indicates the multiplier, and the fourth color circle indicates the error. The multiplier, which is the resistance value of the resistor (in Ω)
▲Due to the manufacturing error of the resistance value, the measurement error of the multimeter, and the error of human eyesight, it is permissible to have a certain error when measuring the resistance value with the multimeter, and it is considered normal if the error is within .
▲When using high resistance gear (RX10K gear or 1K gear) to test the resistance with large resistance value (above tens of KΩ), the reading will become obviously smaller and the measurement error will increase.
▲For a four-color ring resistor: the first color ring represents the effective number, which is the first two digits of the resistance value, and the multiplier is the multiple of the resistance value, so read the effective number of the first two color rings ( write) down, and then multiply by the multiplier, which is its resistance value.
▲When practicing, you can read the resistance value of the color ring resistance according to the color ring reading, and then use the multimeter resistance file to test. If the test value is basically the same as the value you read (error), you can see that the color ring is basically accurate. If the difference between the read values ​​is too large, it is possible that the color of some color circles is wrong. You should re-test and look again until it is accurate.
▲If the resistance value is small, use the low resistance gear (X10 or X1) to test, and if the resistance value is large, use the high resistance gear (X10K or X1K). X100, X10, etc.) test, but the pointer points to the left and right in the close scale. At this time, it is not only easy to see the reading, but also the most accurate reading.
▲Quickly read the four-color ring resistance
Five-color ring resistor (for precision resistors, mostly used in instruments or circuits with high requirements)
The first, second, and third color circles are the significant numbers, the fourth color circle indicates the multiplier, and the fifth color circle indicates the error (note: this color circle is mostly gold, silver, or farther away from other color circles) Multiply the significant number The multiplier is the resistance value of the resistor (unit: Ω)
7. Judgment of the quality of resistance
For ordinary fixed resistance, when testing its resistance value with the multimeter resistance gear, it should be basically the same as the nominal value of the resistance (that is, the resistance value marked on the resistance) (error <±20%), which is normal. If the resistance difference is too large (that is, the error is >±20%), the resistance has changed its value (that is, it has become larger or smaller, and the resistance value is mostly larger, and the resistance value is less common) and cannot be used. If the value becomes infinity (∞), the resistor is open-circuit damaged, and if the resistance value becomes zero (rarely), the resistor is short-circuit damaged.
For trimmer resistors (also called trimmer potentiometers) and adjustable resistors (also known as potentiometers), use the multimeter resistance gear to test the resistance values ​​at both ends of the resistors should be basically the same as their nominal values ​​(error <±20%), which is normal, otherwise the potential defective or damaged device. At the same time, the resistance value between the center head (middle pin) and either end of the test potentiometer should be continuously fine-tuned between zero and the nominal value to be normal, otherwise the potentiometer will be bad or damaged.
For a positive temperature thermistor (PTC), its resistance value should be about tens of tens at room temperature, which is normal. If the resistance value is too large, the internal contact will be poor. If the resistance is infinite, it will be open and damaged. If the resistance value is basically zero , it has been damaged by short circuit, and the resistance value of the resistor will become as large (a few hundred KΩ or more) when it is energized and heated, which is normal.
For a negative temperature coefficient thermistor, its resistance value should be basically the same as its nominal value when tested at room temperature (error) is normal. If the resistance value difference is too large, the resistance is bad or damaged; if the resistance value becomes infinite, the resistance is open and damaged. At the same time, the higher the temperature of the resistance, the smaller the resistance value, and the lower the temperature, the larger the resistance value becomes, which is normal. Otherwise, the negative temperature coefficient thermistor is bad or damaged.
For the varistor, due to its high working voltage (above tens of V), its resistance value should be infinite when testing with the multimeter resistance gear, which is normal (because the battery voltage in the meter is low), otherwise the varistor is bad or damaged , When the varistor is below a certain rated voltage, the resistance value is very large (generally infinite, and its resistance value decreases steadily only when it is large or exceeds its rated voltage.
For humidity sensitive resistors, the resistance value should be reduced (about tens of KΩ) when tested under air-dry conditions; and when there is no strong light irradiation, its resistance value becomes smaller (less than tens of Ω), which is normal. Otherwise the photoresistor is bad or damaged.
8. Fault and maintenance of resistance
For the fixed resistance of thin film (such as carbon film, metal film, etc.) material, if it is damaged, it cannot be repaired, and it can only be replaced.
For wirewound resistors, open-circuit faults often occur. At this time, the resistance wire is blown at a certain position. It may be used after the broken part is welded. If it is a cement (wirewound) resistor, open the casing to find the burnt. After it has been repaired and repaired, it can be used in a cement package and it can be used. Of course, it is better to replace it with a new one.
For fine-tuning resistors, it is easy to use the middle sliding contact piece and the carbon film to make poor contact due to oxidation. At this time, use the potentiometer cleaning agent to solve the problem. If the cleaning is invalid, it can only be solved by replacement.
For the potentiometer, it is easy to cause the failure of the carbon film to wear and make the middle sliding piece (center tap) in poor contact. At this time, the position between the center sliding piece and the carbon film can be adjusted or cleaned with a potentiometer cleaning agent.
For the positive temperature coefficient thermistor (PTC), the fault of poor contact between the resistor and the tablet is most likely to occur. At this time, the tablet can be adjusted and cleaned and repaired. If the resistor body is broken, it cannot be repaired and can only be replaced.
For the negative temperature coefficient thermistor, if it is damaged, it cannot be repaired and can only be replaced.
For varistors and photoresistors, if they are damaged, they cannot be repaired and can only be replaced.
For the humidity sensitive resistor, if it is damaged, it can only be solved by replacing it, but it is difficult to repair. However, when the humidity sensitive resistor of the video recorder, video camera (DV), etc. is damaged and there is no device replacement, a 2,000 ohm can be used in emergency situations. The left and right fixed resistors are replaced, and the moisture detection function will be lost at this time.

Electronic component symbols
2. Capacitors
Referred to as capacitor, it is composed of two or two sets of balanced metal plates with a dielectric (insulating layer) in the middle. It is a device that can store charges and has the characteristics of charge and discharge.
1. Dielectric materials of capacitors
Common dielectric materials such as air, ceramics, mica, polyester, polypropylene, aluminum, silver, etc., electrolytes.
2. The main electrical parameters of the capacitor
Capacity: refers to the amount of storage capacity.
The basic unit of capacity is farad, referred to as method (F).
Withstand voltage: refers to the voltage that the capacitor can withstand when it works for a long time. Withstand voltage: a few V – a few KV
3. Types of capacitors
Fixed non-polar capacitors
Refers to fixed capacitance non-polar capacitors, such as: ceramic (ceramic) capacitors, mica capacitors, film capacitors (such as: polyester, polypropylene and other capacitors)
Trimming (non-polar) capacitors
Refers to a non-polar capacitor whose capacitance can be fine-tuned. (Note: The trimmer capacitors are all non-polar capacitors). Such as: air ceramic, thin film and other trimmer capacitors.
Adjustable Capacitor
Refers to non-polar capacitors with continuously adjustable (variable) capacitance (note: adjustable capacitors are non-polar capacitors). Such as: air, film and other adjustable capacitors. Common ones are single-connection, double-connection, and four-connection adjustable (variable) capacitors.
Electrolytic capacitor
Refers to the use of aluminum, tantalum, niobium and other electrolytes as dielectric capacitors called electrolytic capacitors, most electrolytic capacitors are polar capacitors.
Note: Electrolytic capacitors do not have fine-tuning and adjustable structures, and are all capacitors with fixed capacity.
4. Capacitor withstand voltage representation
Directly indicate the withstand voltage value and unit. Such as: (6V, 25V, 50V, 100V, etc.)
(Note: Electrolytic capacitors generally use this method, other capacitors are generally less used)
Directly indicate the withstand voltage value and omit the unit (V). Such as: 25 is 25V, 63 is 63V, 100 is 100V, etc.
The withstand voltage value is represented by numbers and letters, consisting of a number and a letter. The number represents the multiplier of the withstand voltage of 10, and the letter represents the effective number of the withstand voltage. Multiplying the effective number by the multiplier is the withstand voltage of the capacitor. pressure value.
(Note: It is more common to use this method for polyester capacitors, and this method is less used for other capacitors)
Example: 1A=10V 2A=100V 2B=125V
2C=160V 3D=2KV 3G=4KV
1E=25V 2F=315V 4W=45KV
Use color to indicate pressure resistance
Some ceramic capacitors have colors to indicate their withstand voltage values, that is, different colors on the surface indicate different withstand voltages.
For some imported ceramic (ceramic) capacitors, those with a horizontal line below the capacity are rated at 50V, and those without a horizontal line are rated at 500V.
The withstand voltage unit of some capacitors has WV to represent V, such as: 50WV is 50V, 350WV is 350V, etc.
If the withstand voltage value is not indicated by the above method, the capacitor can be regarded as a low-voltage capacitor with a withstand voltage of 25V (or below).
5. Capacitor capacity representation method
Directly indicate the value and unit of the capacity, such as: 5PF, 33PF, 100PF, 22nf, 0.01uF, 47uF, 22F, etc.
(Note: Most electrolytic capacitors use this method)
Directly indicate the value of the capacity, and the unit uses u, n, p to represent uF, nF, pF, such as: 47u is 47Uf.
Use a few X to represent a few X, such as: 8P2 is 8.2Pf, 6n8 is 6.8Nf, 4u7 is 4.7uF, etc.
Any value of capacitance is expressed in fractions of a few points or a few points without indicating the unit. The unit of its capacity value is a few tenths of uF, such as: 0.01 or 0.01uF, etc.
Capacitance values ​​are integers without indicating units. Its unit is PF (note: the last digit of the three-digit number is not zero). Such as: 3 is about 3PF, 15 is 15PF, 120 is 120PF, etc.
Digital representation: represented by three digits (note: except the last digit is zero), the first and second digits represent the significant number, and the third digit represents the multiplier (1 is 101, 2 is 102, 3 is 103 … 8 is 108, but 9 is 100) Multiply the effective number by the multiplier, which is the capacitance, and its unit is PF.
Color circle (color bar) notation
Same as color ring resistance notation, but in PF
There are manufacturers of capacitor capacity units in capital English MDF or MF to represent uF. Such as: 25MDF is 25uF, 100MF is 100uF.
Some capacitors are marked with letters or positive and negative percentages after the capacitance value to indicate the error level of the capacitor.
Note: The capacitance error levels of most manufacturers are represented by the above letters, but some manufacturers are represented by other letters or characters, and the error levels are not listed here.
6. Polarity distinction of polar electrolytic capacitors
For uncut aluminum electrolytic capacitors, the long leg is positive and the short leg is negative.
Polarized capacitors are required to be marked with positive and negative poles before leaving the factory (positive and negative poles can be marked, or only positive or negative poles can be marked), which can be seen directly from the outer casing of the capacitor.
Use the resistance gear of the multimeter to test the positive and negative electrodes (for reference only) When testing the forward and reverse leakage resistance (that is, the insulation resistance is large) of the polar electrolytic capacitor with the highest range of the resistance gear of the multimeter (RX1K or 10K), the reverse The characteristics of large leakage (that is, low insulation resistance). When testing, the hand first swings to the right (the larger the capacity, the larger the hand swings), and then slowly retreats to the left. If the needle can return to infinity (the starting position on the left side of the scale), the capacitance basically has no leakage. If the needle cannot return to the infinite position and stops at a certain scale, the resistance value at this time is leakage resistance (that is, insulation resistance). Resistance) repeatedly test for many times (the test pen should be replaced) to test its forward and reverse leakage (insulation resistance). When the leakage is small (that is, the insulation resistance is large), the electrode connected to the black test lead is the positive electrode of the electrolytic capacitor and the red test lead is connected to the negative electrode. Otherwise, the polarity of the test lead is just the opposite.
Note: The black test lead is connected to the positive electrode of the electrolytic capacitor and the red test lead is connected to the negative electrode to test the forward leakage resistance.
The red test lead is connected to the negative electrode of the electrolytic capacitor and the black test lead is connected to the positive electrode to test the negative leakage resistance.
7. Capacitance withstand voltage test
The withstand voltage of the capacitor can be directly seen from the appearance of the capacitor without testing, but if there is a withstand voltage meter, it can also be directly tested with a withstand voltage meter.
8. Capacitor capacity test
For qualified capacitors, the capacity is the value marked on the capacitor shell, which can generally be seen directly without testing.
If there is a capacitance meter (some digital multimeters can also test capacitance capacity, but can only test small capacitance capacity and cannot measure large capacitance capacity). You can use the capacitance meter to directly test the capacity of the capacitor.Some pointer multimeters can also measure their capacitance when they are connected in series with alternating current of a certain voltage value, but the error is large and it is not recommended to use them.
The capacity of the capacitor can also be roughly measured with an ordinary mechanical pointer multimeter. The method is to use the resistance gear of the multimeter (the high resistance gear should be used for small capacity, and the low resistance gear should be used for large capacity). Replacing the test leads for many times, the larger the capacitance, the greater the swing of the needle, and the smaller the capacity, the smaller the swing of the needle. According to the comparison between the swing of the needle and its standard capacity, the capacity of the capacitor can be estimated ( Note: Under normal circumstances, the capacity of the capacitor does not need to be particularly accurate, and the capacitor can be used normally only if it is within a certain range. In general, only a rough test of the capacity of the capacitor can be performed with an ordinary pointer multimeter).
Note: When the capacity is large and the high-resistance gear is used to test, the needle will exceed the scale line and it is difficult to compare the capacity. At this time, the range test is reduced to the limit that the needle does not exceed the scale, so that the capacity can be compared.
▲If the capacity is too small (less than 0.01uF), the highest resistance level test is required to see that the needle swing is normal. For these capacitors, it is difficult to compare the capacity with the resistance level, and only the capacitance meter is used to test.
▲If the needle stops at zero ohm and cannot be returned during the test, then the capacitor has been short-circuited and damaged, and its capacity cannot be tested.
9. Capacitive reactance
The equivalent resistance of a capacitor to alternating current is called capacitive reactance.
10. Characteristics of capacitors
It has the characteristics of passing high frequency and blocking low frequency, and passing AC and blocking DC.
a) Use of capacitors
It can be used for filtering, coupling, decoupling, bypassing, tuning, resonance and other purposes.
b) Judgment of the quality of the capacitor
Use a multimeter to judge the resistance gear (small capacity must use high resistance gear and large capacity can use low resistance gear) when testing capacitors (should replace the test pen for many times or test the capacitor after short-circuiting and discharging), the larger the capacity, the greater the swing of the needle. And after the needle swings, it should slowly return to normal (that is, only in this way the capacitor is good). If compared with a capacitor of the same capacity, if the swing range of the test needle is too small and the power does not swing at all, the capacitance of the capacitor has become smaller or failed and damaged, and the swing of the needle should be slowly returned (small capacity, fast return speed, and large capacity, slow return speed ). If the needle stops at a certain position, the resistance at this time is the leakage resistance of the capacitor. The larger the leakage resistance, the better (preferably infinite). If the leakage resistance is too small, the leakage of the capacitor will be too large and the performance will be poor. If the leakage resistance is basically zero (that is, the needle stops at zero ohms on the scale), the capacitor has been short-circuited. (breakdown) damage. It is normal that it is difficult to see the needle swing at the highest grade of the resistance gear for capacitors with small capacity. However, if the capacitor has leakage or breakdown short circuit, it may be tested (Note: For such capacitors with leakage or breakdown, it can be considered that the capacitor has poor performance or damage and should not be used)
For non-polar capacitors with a capacity greater than 1uF, when testing with the RX1K or 10K gear of the resistance gear of the multimeter, it should be obvious that the needle swings to the right and then returns to the infinity position quickly, which is normal. If it cannot be returned to the infinite position, the capacitor has leakage and it is best not to use it. If the leakage resistance is basically zero, the capacitor has been broken down and short-circuited.
For non-polar capacitors with a capacity greater than 0.01uF (10uF) but less than 1uF, use the highest range of the resistance range (it is best to use the RX10K range, some capacitors are difficult to observe when using the X1K range), and you should see the needle swing slightly during the test ( That is, it is normal to return to the infinite position soon after the needle swings very small), and there should be no leakage or short circuit, otherwise the capacitor will be bad or damaged.
For non-polar capacitors with a capacity less than 0.01uF (10nF is 10000pF), use the highest range of the multimeter’s resistance range (for example: it is difficult to see the needle swing during the test (because the capacity is too small, the capacitor has been charged when the probe just touches the capacitor). It is normal that the needle has no time to swing. If it is suspected that the capacitance of these capacitors becomes smaller or fails, it can only be tested with a capacitance meter or the substitution method in practical applications (substitution method) is to replace the suspected damaged one with a good one.) Judgment, these capacitors must not have leakage power short-circuit phenomenon during the test, otherwise it can be considered that the capacitor is damaged and can not continue to use.
For polar electrolytic capacitors, due to the large capacity, the appropriate gear range can be selected for testing according to the size of the capacity (that is, high-grade for small capacity and low-grade for large capacity, such as: X10K or X1K gear below 10uF, X1K or X100 can be used at about 100uF, X100 or X100 can be used below 1000uF, RX10 or above can be used above 1000uF, the above gear selection is for reference) The larger the capacity, the larger the needle swing. (Comparison of the same position and range) and the needle should slowly return to normal after swinging. The needle returns to a certain scale position and stops but cannot return to infinity (that is, the starting position of the needle scale), it indicates that the capacitor has leakage. The smaller the leakage (that is, the greater the leakage resistance), the better, The smaller the leakage resistance), the poor performance of the capacitor. If the leakage resistance is basically zero, the capacitor has been broken down and damaged. At the same time, because the electrolytic capacitor has the characteristics of small forward leakage (that is, large leakage resistance) and large reverse leakage (that is, small leakage resistance). Therefore, the forward leakage of the test is generally small, and the reverse leakage is not considered. For polar electrolytic capacitors, if the storage time is too long, the leakage will become larger, as long as it is used for a period of time or even tested many times. Leakage will also be reduced.
three. Inductor
Referred to as inductance, commonly known as coil, is an inductive component made of coils.
1. Types of Inductors
Air core inductance: refers to the inductance in which the coil is wound on a hollow support or directly wound.
Magnetic core inductance: refers to the coil wound on the magnetic core (that is, the coil has a magnetic core inside).
Copper core inductance: refers to the inductance of the coil wound on the copper core.
Iron core inductance: refers to the inductance of the coil wound on the iron core.
Tapped Inductance: Refers to the inductance with one or more taps drawn from the coil.
2. Inductance
Refers to the amount of inductance capacity, called inductance. The basic unit of inductance is Henry, abbreviated as Henry (H), and the commonly used units are millihenry (mH), microhenry (μH) and so on.
1H=103 mH=106μH
3. Inductive reactance (XL)
Refers to the resistance of inductance to alternating current (ie equivalent resistance). XL=2лfL
4. Characteristics of Inductors
It has the characteristics of passing DC and blocking AC, and passing low frequency and blocking high frequency.
5. Self-inductance effect of inductance
When the current passing through the inductance coil changes, the coil will generate a self-inductive electromotive force to hinder the change of the current. This effect is called the self-inductance effect of the inductance.
6. Mutual Inductance of Inductors
Two coils that are close to each other, when one has a changing current, the other will also induce an induced electromotive force. This effect is called the mutual inductance effect of the inductance. Transformers are made according to the principle of mutual inductance.
7. The use of inductors
It can be used for filtering, wave blocking, current limiting, transformation, tuning, vibration elimination, etc.
8. Representation of inductance
Directly indicate the value and unit of the inductance. Such as: 10mH, 150μH.
Use a few X to represent a few X. Such as: 1H2 is 1.2H, 3m3 is 3.3mH, 8μ2 is 8.2μH.
Representation by color circle or color point: it is represented by a four-color circle (color point), the first two-color circle (color point) represents the significant number, the third color circle (color point) represents the multiplier, and the fourth color circle (color point) represents the multiplier. Indicates error. (Same as the four-color ring resistance representation method)
Gray red brown gold is 82X101±5%
Expressed by number of turns (number of turns)
Some inductive coils do not indicate their inductance but directly indicate the number of turns (turns) that the inductive coil should be wound, such as: 3T means 3 turns (turns), 19T means 19 turns, etc.
There are many inductance coils made by the manufacturer, which have neither inductance nor the number of turns to be wound. In practical applications, they can only be replaced with the same coil or rewound according to the original specifications.
9. Inductor (coil) judgment
The resistance of the multimeter can be used to roughly test the quality of the inductance coil. The method is to compare the DC resistance at both ends of the coil with the normal value or the same coil. If the resistance value is basically the same (error ≤±10%), it can be considered that the coil is good. If the resistance value difference is too large, the coil is defective; if the resistance value becomes infinite, the coil is open-circuit damaged; if the resistance value becomes zero, the coil is short-circuit damaged.
10. Troubleshoot and Repair of Inductor Coil
If the inductance coil is short-circuited or partially short-circuited, the coil should be disassembled and rewound according to the original specifications to repair.
If the inductance coil has poor internal contact or open circuit fault, you can carefully disassemble the coil for inspection. The poor contact (mostly at the coil joint) or the open circuit can be repaired by re-soldering firmly, or by rewinding with a new wire according to the original specifications. .
In most cases, if the inductor coil is faulty, it is recommended to replace it if there are new spare parts, and only repair it if there is no new spare part.
Four. transformer
A transformer is a multi-coil device that can transform AC voltage, current and impedance.
1. Transformer transforms the relationship between AC voltage, current and impedance:
N1, N2 are the number of turns of the primary; U1, U2 are the voltage of the primary; I1, I2 are the current of the primary; Z1, Z2 are the impedance of the primary. The primary coil (N1) is also called the primary coil; the secondary coil (N2) is also called the secondary coil.
The primary and secondary turns ratio of the transformer is proportional to the primary and secondary voltage, inversely proportional to the primary and secondary current, and proportional to the square root of the primary and secondary impedance. The formula is expressed as:
2. Types of transformers
High-frequency transformer: refers to the transformer used to transform high-frequency electrical signals. Such as antenna coils, oscillating transformers, etc.
Intermediate frequency transformer: (commonly known as Zhongzhou): refers to the transformer used in the super-heterodyne radio receiver to transform the medium-to-electrical signal.
Low-frequency transformer: refers to a transformer used to transform low-frequency electrical signals, such as audio transformers.
Power transformer: refers to the transformer used to convert AC mains.
Autotransformer: refers to the transformer that can be shared by the primary and secondary coils.
3. The judgment of the quality of the transformer
The resistance of the multimeter can be used to roughly judge the quality of the transformer. The method is to measure the DC resistance of each coil of the transformer and compare it with the normal value or a good transformer. If the resistance of all coils is normal, it can be considered that the transformer is good; if there is a or multiple coils are bad or damaged. At the same time, it is normal to test the insulation resistance between different coils or between each coil and the shell (iron core) to be infinite, otherwise the transformer is also bad or damaged.
4. Transformer Troubleshooting and Repair
A transformer with a thermal fuse connected in series with the primary coil of the transformer, if the primary open circuit occurs, it is mostly caused by the thermal fuse blown, which can be solved by replacing a thermal fuse.
For general transformers, if the coil is damaged, it can be repaired by rewinding according to the parameters of the original coil.
In most cases, the damage to the transformer is difficult to repair or the repair project is too large, it is recommended to replace it.
5. Transformer parameters and calculations
Core cross-sectional area (S): S = tongue width × stack thickness
The relationship between the iron core cross-sectional area (S) and the transformer power (P): S=1.25
Number of turns per volt (N): refers to the number of coil turns (turns) that should be wound per volt
f is the frequency of alternating current, S is the cross-sectional area of ​​the iron core, and Bmax is the magnetic induction intensity
Primary turns (N1) and secondary turns (N2)
N1=U1N (U1 is the primary voltage); N2=U2N (U2 is the secondary voltage)
Wire diameter (d): refers to the diameter (mm) of the wire wound around the coil.
I is the current of the wire (I=P/U)
Primary wire diameter d1=; Secondary wire diameter
five. Semiconductor (Crystal) Diode (D)
Abbreviated as diode, it is a semiconductor device with a double-layer structure, which is composed of a PN junction and has the characteristics of unidirectional conduction.
1. PN junction
P-type semiconductor: refers to an impurity semiconductor in which the majority of holes are carriers.
N-type semiconductor: refers to an impurity semiconductor in which electrons are majority carriers.
PN junction: The space formed at the interface of the P-type semiconductor and the N-type semiconductor, the charge region (ie the blocking layer) is called the PN junction.
The characteristics of PN junction: it has the characteristics of unidirectional conduction.
2. The main electrical parameters of the diode
Forward current: Refers to the electrical current that is allowed to pass in forward conduction.
Reverse breakdown voltage: refers to the electrical high voltage when the PN junction reverses breakdown, that is, the withstand voltage of the diode.
Forward Conduction Voltage: Refers to the voltage required for forward conduction. Germanium material (PN junction): 0.2V (0.2-0.3V); silicon material (PN junction): 0.6V (0.5-0.7V); compound material about 2V (1-3V).
Junction capacitance: The capacitance formed by the PN junction is called junction capacitance.
3. Purpose of Diodes
It can be used for rectification, voltage regulation, switching, damping, tuning and other purposes.
4. Diode polarity judgment
For ordinary diodes, one end with a logo (such as a color circle) is negative and the other end is positive.
For light-emitting diodes, if the legs are not cut, the long leg is the positive electrode, and the short leg is the negative electrode.
For diodes, most of the positive and negative electrodes can be directly seen from their internal structure.
Judging by the resistance gear of the multimeter: When using the resistance gear of the multimeter to test the forward and reverse resistance of the diode, it is judged according to the characteristics of the PN junction of the diode having a small forward resistance and a large reverse resistance. During the test, when the resistance is small, the black test lead is connected to the positive electrode, and the red test lead is connected to the negative electrode.
5. Judgment of the quality of diode (PN junction)
When using the multimeter resistance gear to test the forward and reverse resistance of the diode, the smaller the forward resistance of the diode (PN junction), the better, and the larger the reverse resistance, the better. If the forward and reverse resistance of the diode are very small or large, the tube has been broken down and short-circuited or damaged by open-circuit.
six. Semiconductor (crystal) triode
A triode is a three-layer semiconductor device that amplifies and switches signals, and consists of two PN junctions.
1. The structure of the triode
The triode is divided into two types of structure: PNP type and NPN type.
E or e for emitter, B or b for base, C or c for collector, BC junction (bc junction): collector junction
BE junction (be junction): launch junction
2. The main electrical parameters of the triode
PCM: refers to the maximum dissipated power of the collector, which is the maximum power of the triode. PCM<1W is a low-power tube; PCM>1W is a high-power tube; PCM=1W or so is a medium-power tube.
ICM: refers to the maximum current of the collector, which is the maximum current of the triode.
Bvceo: refers to the maximum reverse breakdown voltage of the collector and the emitter when the base is open, that is, the withstand voltage of the triode.
Iceo: refers to the maximum reverse leakage current between the collector and the emitter when the base is open, that is, the penetration current of the triode.
fT: refers to the characteristic frequency, that is, the frequency when the amplification factor drops to 1 in its emitter amplifier circuit.
fT≤3MHz is a low frequency tube; fT>3MHz is a high frequency tube; fT> several hundred MHz is called an ultra-high frequency tube
hFE: refers to the DC amplification factor of the triode (DC amplification factor)
hFE= (Ic is the collector current, IB is the base current)
β value: refers to the AC magnification of the triode
(ΔIC is the change in collector current, ΔIB is the change in base current)
3. Distinguishing between PNP type and NPN type
When using the multimeter resistance gear to test the forward and reverse resistance between the legs of the triode, if the red test lead is connected to a fixed electrode once, and the black test lead is connected to the other two electrodes, the resistance is relatively small, then this tube is a PNP tube (referred to as P). tube), and the electrode connected to the red test lead is the base electrode; if there is a black test lead connected to a fixed electrode, the red test lead is connected to the other two electrodes, and the resistance is relatively small.Then this tube is a PNP tube (referred to as P tube), and the electrode connected to the red test lead is the base electrode; if there is a black test lead connected to a fixed electrode once, and the red test lead is connected to the other two electrodes, the resistance is relatively small, then this tube is NPN tube (referred to as N tube) and the black test lead is connected to the base.
4. The three electrodes of the triode are distinguished
After judging the PNP and NPN tubes according to the above method and finding the base, the remaining two electrodes can be judged by the following method. If it is a PNP type tube, connect a resistor of about 100K between the electrode connected to the red test lead and the base (this resistance can be replaced by a finger). If the needle changes significantly, the electrode connected to the red test lead is the collector, and The electrode connected to the black test lead is the emitter; if this tube is an NPN type tube, the polarity of the test lead is just the opposite, and the test method is exactly the same as that of the PNP type tube.
5. The principle of amplification of triode
The base current has a small change, and the collector current has a large change, that is, a small current is used to control a large current to achieve current amplification, which is the principle of the amplification of the triode.
6. Judgment of the quality of the triode
Use the resistance gear of the multimeter to test the forward resistance of the two PN junctions (emitter junction and collector junction, namely be junction and bc junction) of the triode. The larger the forward resistance (more than tens of K ohms in the Rx1K test, and most tubes are infinite), the better, if the forward resistance of two or one of the PN junctions is too large (for example, the Rx1K test has tens of ohms) above) or the reverse resistance is too small (for example, the Rx1K gear test is less than tens of K ohms), the performance of the tube is poor, if the forward and reverse resistances of two or one of the PN junctions are very small (such as basically zero) or very If it is large (such as basically infinite), the tube is damaged due to two or one PN junction breakdown or open circuit. At the same time, the larger the positive and negative resistance between the collector and the emitter (preferably infinite, but some tubes are more than tens of K ohms), the better the sink is. If the resistance of the tube is too small, the penetration current of the tube is too large and the performance is poor. If the resistance is basically zero, the tube has been broken down and damaged. It is also necessary to use the HFE file to measure or use the resistance file to estimate the amplification of the triode. Capacity (HFE value), different types of tubes have different magnification capabilities, but they should have magnification capabilities (the HFE value should be several times more, and tubes without magnification capabilities cannot be used.)
7. Trouble and Repair of Triode
. When the performance of the triode is poor or damaged, the triode cannot be trimmed and can only be solved by replacing it with a new or good triode.
. When the triode is damaged, it should be replaced with a tube of the same type as far as possible. If there are no pipes of the same type, pipes with the same or similar performance parameters should be selected.
When choosing a substitute pipe, its parameters Icm, Pcm, Bvceo and other parameters should be equal to or greater than the original type of pipe before it can be replaced.
Low-frequency tubes can only be used in low-frequency circuits, while high-frequency tubes can be used not only in high-frequency circuits but also in low-frequency circuits. Therefore, in practical applications, high-frequency tubes can replace low-frequency tubes, but not vice versa.
seven. Nomenclature of semiconductor devices
1. China
Composed of numbers—letters—letters—numbers—(letters)
The first number indicates the number of electrodes, such as: 2 – diode, 3 – triode
The second letter indicates the material and polarity, such as: A – germanium material PNP type B – germanium material NPN type
C——Silicon material PNP type D——Silicon material NPN type E——Compound material
The third letter indicates the type of device, such as:
G——High frequency small power tube A——High frequency high power tube
X——Low frequency small power tube D——Low frequency high power tube
K——switch tube W——voltage regulator tube P——common tube E——rectifier tube N——damping tube B——varactor tube
The fourth number indicates the registration number
The fifth letter, using the letters A, B, C, D, etc. to represent the improvement of the prototype
Example: 2AP9 – germanium ordinary diode 2CW56 – silicon Zener diode 3DG6B – silicon NPN type high frequency low power transistor is an improved version of 3DG6 3AX31 – germanium PNP type low frequency low power transistor 3BX31 – germanium NPN type low frequency low power Transistor 3CD511——Silicon PNP type low frequency high power triode 3DD15——Silicon NPN type low frequency high power triode
2. Japan
Composed of numbers – letters – letters – numbers – (letters)
The first number is expressed as: 0 – phototransistor; 1 – diode and rectifier; 2 – triode and controllable rectifier.
The second letter “S” denotes a semiconductor device.
The third letter indicates the type of device, the first item is 0, and the third item of 1 is absent.
A——pnp type for high frequency B——PNP type for low frequency C——NPN type for high frequency D——NPN type for low frequency
J——P channel field effect transistor K——N channel field effect transistor
The fourth number represents the registration number.
The fifth letter is used to distinguish the prototype from the variant, and the letters A, B, C, D, etc. are used to represent the improvement of the prototype.
Example: 2SC1815, 2SA1015, 2SC1942, 2SD3298A, 2SD1555, 2SK134, etc. Note: Japanese model transistors often omit the “2S” in front of the model for the convenience of marking, such as: A1015, C1815, C3298A, D1555, etc.
3. Europe
It consists of letters – letters – numbers – (letters).
The first letter indicates the type of device used.
A——Germanium material B——Silicon material
The second letter indicates the type of device.
A——detection, switch, mixing triode; B——varactor diode; C——low frequency low power tube; F——high frequency low power tube; D——low frequency low power tube; L——high frequency high power tube; S – low power switch tube; U – high power switch tube: E – voltage regulator tube; Y – rectifier tube.
The third number represents the registration number.
The special device uses an alphanumeric two-digit number to indicate the registration serial number; the general-purpose device three-digit number represents the registration serial number.
The fourth letter, through the letters A, B, C, D, etc., represents the improvement of the prototype or the mark of a certain number of grades.
Example: BF198——is a general-purpose device, silicon NPN type high-frequency low-power transistor; BUY71——is a special device, silicon NPN type high-power switching triode.
4. U.S.
It consists of numbers – letters – numbers – (letters).
The first number and the second letter “N” are expressed as: 1N – diode and rectifier; 2N – triode and controllable rectifier; 3N – tetrode.
The third number represents the registration number.
The fourth letter, with A, B, C, D, etc., represents the improvement of the prototype. Example: 1N4007, 2N3055, etc.
5. Digital triodes from Samsung, such as: 9011, 9012, 9013, 9014, 9015, 9016, 9018, etc.
Eight. Integrated Circuit (IC)
Integrated circuit (integrated circuit, Hong Kong and Taiwan called integrated circuit) is a miniature electronic device or component. Using a certain process, components and wirings such as transistors, diodes, resistors, capacitors and inductors required in a circuit are interconnected, fabricated on a small or several small semiconductor wafers or dielectric substrates, and then packaged in a tube. Inside the shell, it becomes a miniature structure with the required circuit function; all the components are structurally integrated, so that the volume of the entire circuit is greatly reduced, and the number of lead-out lines and soldering points is also greatly reduced, so that the electronic components A big step towards miniaturization, low power consumption and high reliability.
Integrated circuits have the advantages of small size, light weight, less lead-out lines and solder joints, long life, high reliability, and good performance, and at the same time, low cost and easy mass production. It is not only widely used in industrial and civil electronic equipment such as tape recorders, televisions, computers, etc., but also in military, communications, remote control, etc. Using integrated circuits to assemble electronic equipment, its assembly density can be increased by dozens to thousands of times compared with transistors, and the stable working time of the equipment can also be greatly improved.
It is represented in the circuit by the letters “IC” (also with the text symbol “N”, etc.).
1. Classification of integrated circuits
(1) Classification by functional structure
According to their different functions and structures, integrated circuits can be divided into three categories: analog integrated circuits, digital integrated circuits and digital/analog hybrid integrated circuits.
Analog integrated circuits, also known as linear circuits, are used to generate, amplify and process various analog signals (referring to signals whose amplitude varies with the time boundary. For example, audio signals of semiconductor radios, tape signals of VCRs, etc.), its input signals and output signals proportional relationship. Digital integrated circuits are used to generate, amplify and process various digital signals (referring to signals with discrete values ​​in time and amplitude. For example, audio signals and video signals played by VCD and DVD).
(2) Classification by production process
Integrated circuits can be divided into semiconductor integrated circuits and thin film integrated circuits according to the manufacturing process.
Film integrated circuits are further classified into thick film integrated circuits and thin film integrated circuits.
(3) Classification according to the level of integration
Integrated circuits can be divided into small-scale integrated circuits, medium-scale integrated circuits, large-scale integrated circuits, ultra-large-scale integrated circuits, ultra-large-scale integrated circuits, and huge-scale integrated circuits according to the level of integration.
(4) According to different types of conductivity
Integrated circuits can be divided into bipolar integrated circuits and unipolar integrated circuits according to their conductivity types, and they are all digital integrated circuits.
The production process of bipolar integrated circuits is complicated and the power consumption is relatively large, which means that there are TTL, ECL, HTL, LST-TL, STTL and other types of integrated circuits. The production process of unipolar integrated circuits is simple, the power consumption is also low, and it is easy to be made into large-scale integrated circuits. The representative integrated circuits are CMOS, NMOS, PMOS and other types.
(5) Classification by use
Integrated circuits can be divided into integrated circuits for TV sets, integrated circuits for audio, integrated circuits for DVD players, integrated circuits for video recorders, integrated circuits for computers (microcomputers), integrated circuits for electronic organs, integrated circuits for communication, and integrated circuits for cameras. Circuits, remote control integrated circuits, language integrated circuits, integrated circuits for alarms and various special integrated circuits.
(6) According to the application field
Integrated circuits can be divided into standard general-purpose integrated circuits and application-specific integrated circuits according to application fields.
(7) According to the shape

Integrated circuits can be divided into round (metal case transistor package type, generally suitable for high power), flat type (good stability, small size) and dual in-line type according to the shape.
2. Package Types of Integrated Circuits
In-line package
The in-line package integrated circuit is a form of integrated circuit package in which the pins are inserted into the printed board and then soldered. There are mainly single-line package and dual-line package. Among them, the single inline package includes a single inline package (SingleInlinePackage, abbreviated as SIP) and a single inline package (Zig-ZagInlinePackage, abbreviated as ZIP). The packaged integrated circuit has a row of pins and is divided into two rows for installation.Dual in-line package is also called DIP package (DualInlinePackage). This packaged integrated circuit has two rows of pins. It is suitable for through-hole mounting of PCB; easy to install on PCB Wiring; easy installation. The structure of dual in-line package mainly includes multi-layer ceramic dual-in-line package, single-layer ceramic dual-in-line package, lead frame package and so on.
. SMD package
With the improvement of production technology, the volume of electronic products is getting smaller and smaller, and the larger in-line package integrated circuits can no longer meet the needs. Therefore, the designer has developed a chip packaged integrated circuit. The packaged integrated circuit has very small pins and can be directly soldered to the printed wire of the printed circuit board. SMD packaged integrated circuits mainly include thin QFP (TQFP), fine pitch QFP (VQFP), reduced QFP (SQFP), plastic QFP (PQFP), metal QFP (MetalQFP), tape carrier QFP (TapeQFP), J Small Outline Package (SOJ), Thin Small Outline Package (TSOP), Very Small Outline Package (VSOP), Shrinked SOP (SSOP), Thin Shrinked SOP (TSSOP) and Small Outline Integrated Circuit (SOIC) and other derived packages.
. BGA package (Ball Grid ArrayPackage)
Also known as ball grid array package, the pins of the BGA package are distributed under the package in an array of circular or columnar solder joints. The integrated circuits using this package form mainly include high-density, high-performance, multi-functional integrated circuits such as CPU and north and south bridges.
The advantages of BGA packaged integrated circuits are that although the number of pins is increased, the pin spacing has not decreased but increased, thereby improving the assembly yield; the thickness and weight are reduced compared with the previous packaging technology; parasitic parameters are reduced , the signal transmission delay is small, the frequency of use is greatly improved; the assembly can be coplanar welding, and the reliability is high.
. Thick Film Package Thick Film
An integrated circuit is a modular integrated circuit that integrates a dedicated integrated circuit chip and related capacitors and resistance elements on a substrate, and then adopts a standard package form outside of it, and leads out pins.
3. Judgment of the quality of integrated circuits
Measuring Internal Resistance Method
Use the R×1K gear of the resistance gear of the multimeter to measure the forward and reverse resistance of each foot to the ground or between the feet when the IC is not on the circuit, and compare it with the normal value or a good IC. If the resistance value is basically the same (error ≤±10%), it can be considered that the IC is good; if the resistance value of some or all of the pins is too different, the IC is bad or damaged.
Measuring in-circuit resistance method
Use the R×1K gear of the resistance gear of the multimeter to measure the forward and reverse resistance values ​​of the IC pins to the ground (referring to the ground wire of the circuit board) on the circuit board and compare them with the normal value or a good circuit board. If the resistance value is basically the same (error ≤±10%), it can be considered that the IC is good; if the resistance value of some or all of the pins is too different, then the IC is bad or damaged if some or all of the peripheral circuit components of the pins are normal.
Measuring DC working voltage method
Use the DC voltage range of a multimeter to measure the DC working voltage of each pin of the IC to the ground and compare it with the normal value or a good circuit. If the voltage value is basically the same (error ≤±10%), the IC can be considered as good; if the voltage value error is too high If it is large, it means that the IC is defective or damaged when the peripheral circuit components of the corresponding pins are checked to be normal.
Substitution method
When checking the peripheral components of the integrated circuit, the IC cannot work normally, and a good IC can be used to replace the suspected damaged IC. If the circuit can work normally after the replacement, it means that the original IC is defective or damaged; If the circuit still does not work properly, the original IC may not be damaged, and you should continue to check the peripheral circuit components.
Nine. speaker
Commonly known as a speaker, it is an electro-acoustic conversion device that can convert audio electrical signals into sound.
1. Types of speakers
Piezoelectric ceramic horn: It is composed of piezoelectric ceramics, and it emits sound according to the principle of piezoelectric effect.
Electric horn: It is composed of permanent magnet, voice coil, paper plate, diaphragm, etc. The sounding principle is: according to the principle that the magnetic poles of the same sex repel each other and the magnetic poles of the opposite sex attract each other, when the voice coil passes the audio electric signal, it will generate an audio electromagnetic field and the magnetic field generated by the permanent magnet will generate an interaction force, so the voice coil drives the paper plate to move. , so that the tray vibrates the air and makes a sound.
2. The main electrical parameters of the speaker
Power: divided into minimum power and maximum power
Minimum power (PMIN): Also known as undistorted power, it refers to the power whose distortion is within the rated range.
Maximum power (PMAX): Also known as peak power, it refers to the maximum power that the speaker can withstand.
Impedance: refers to the equivalent resistance of the speaker to the audio signal. Impedance = DC resistance of the voice coil + inductive reactance of the voice coil.
Frequency characteristics: refers to the frequency range of the speaker reproduced sound, full-range treble, midrange, bass, etc. The frequency range of sound is 20Hz – 20KHz.
Diameter: refers to the diameter of the horn paper tray.
3. Judgment of the quality of the speakers
Use the 1Ω range of the multimeter resistance range to roughly judge the quality of the speaker. The method is: the DC resistance of the test voice coil should be slightly less than the impedance value of the speaker, and the speaker should be able to make a “click” sound during the test, which is normal. If the DC resistance is too small, the voice coil will be damaged by short circuit. It has been opened and damaged, and at the same time, lightly press the paper tray with your hand, it should have good elasticity, and there should be no noise, otherwise the speaker will also be bad.
4. Phase judgment of speakers
It can be directly seen from the speaker terminal that the plus sign (+) is positive phase, and the minus sign (-) is negative phase.
Use the lowest range of the multimeter’s DC voltage (current) range (eg: 0.5V range) to connect the red and black test pens to both ends of the speaker terminal, and then gently press the paper plate with your hand. Just the opposite.
5. The failure and maintenance of the speaker
When the speaker is faulty, it is recommended to replace it with a new speaker of the same model, but it can also be repaired when there is no new speaker to replace or if you want to reduce the repair cost.
Repair of broken voice coil lead wire: When the speaker is used for a long time or the quality of the lead wire is too poor, the voice coil lead wire is easily broken due to the vibration of the paper tray. At this time, it can be replaced with the same or similar special braided soft wire for the speaker. repair. Note: Please do not replace it with other hard wires or flower wires, otherwise not only the sound quality will be affected, but also the lead wires will be easily broken again.
If the voice coil is damaged, use ΩΩ Tianna water (banana water) to soak the dust cover and the old voice coil, and then replace it with a voice coil of the same type (which can also be wound by yourself). The position of the voice coil is used to fix the new voice coil with adhesive. If it is difficult to separate the original position, you can also install the voice coil connection first and then pass in the sound signal to adjust the position of the voice coil to make the sound the loudest and the best sound quality, and then use the adhesive. The mixture can be repaired after it has been cured and dried.
If the paper tray is damaged, it can be repaired by repairing the damaged area with the same paper tray material. If the paper tray is seriously damaged, it can only be solved by replacing it with a new paper tray.
If the iron core and the permanent magnet are loose and displaced, which leads to collision with the voice coil, it is generally difficult to repair under amateur conditions, and it is recommended to replace it with a new speaker.
For the dome tweeter, since the voice coil and the paper plate (diaphragm) are integrated, if the voice coil is damaged, disassemble the old voice coil assembly and replace it with a new voice coil. ).
11. Crystals and Filters
1. Crystal: Also known as crystal oscillator, crystal oscillator, resonator, etc. It consists of quartz wafers or piezoelectric ceramic sheets, and is often used in oscillator circuits.
2. Filter: Common crystal filters and ceramic filters are used for frequency selection or filtering of signals of a certain frequency.
3. SAW filter: composed of interdigital transducers
12. Composite devices
Refers to a device manufactured or combined with multiple identical or different devices, called a composite device.
1. Resistive recombination
Use multiple resistors with exactly the same resistance to connect one end together as a resistor row formed by a common terminal.
2. Capacitive recombination
A plurality of single capacitors with the same capacity are used to connect one end of them in parallel as a capacitor bank formed by a common terminal, or they are packaged together in the same manufacturing process.
3. Inductor and Capacitor Compounding
It refers to the connection of multiple inductor coils and capacitors in a certain connection mode, which is mostly used in filters.
4. half bridge stack
It is composed of two rectifier diodes packaged together, and is mostly used in rectifier circuits.
5. full bridge stack
Referred to as a bridge stack, it is composed of four rectifier diodes connected together in a certain way, and is often used in rectifier circuits.
6. With divider resistor (band resistance) triode
Refers to a triode with a voltage divider resistor connected between the base and the emitter.
7. Triode with Damping Diode and Shunt Resistor
8. Composite Tube (Darlington Tube)
It is composed of two triodes, the polarity of the composite tube is the same as that of the front tube, and the magnification of the composite tube is the product of the magnification of the two tubes.
9. optocoupler
A light-emitting diode and a phototransistor are packaged together to form an optocoupler.
Common four-pin optocouplers and six-pin optocouplers

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