Basic knowledge of electronic circuits

Basic knowledge of electronic circuits

Basic knowledge of circuits (I)
Basic knowledge of circuits (1) - Resistance
The resistance of a conductor to the current is called resistance, which is represented by the symbol R. The units are ohms, kilohms, and megohms, which are represented by Ω, KΩ, and MΩ respectively.
1. Naming method of resistor models:
The model of domestic resistors consists of four parts (not applicable to sensitive resistors)
The first part: the main name, represented by letters, indicating the name of the product. For example, R represents resistors and W represents potentiometers.
The second part: materials, represented by letters, indicating what materials the resistor body is made of, T-carbon film, H-synthetic carbon film, S-organic solid, N-inorganic solid, J-metal film, Y-nitride film, C-deposited film, I-glass glaze film, X-wire wound.
The third part: classification, generally represented by numbers, and individual types are represented by letters, indicating what type of product it belongs to. 1-ordinary, 2-ordinary, 3-ultra-high frequency, 4-high resistance, 5-high temperature, 6-precision, 7-precision, 8-high voltage, 9-special, G-high power, T-adjustable.
Part 4: Serial number, expressed in numbers, indicates different varieties of similar products to distinguish the product's appearance size and performance indicators, etc.
For example: RT 1 1 type ordinary carbon film resistor a1}
2. Classification of resistors
1. Wirewound resistors: general-purpose wirewound resistors, precision wirewound resistors, high-power wirewound resistors, high-frequency wirewound resistors.
2. Thin film resistors: carbon film resistors, synthetic carbon film resistors, metal film resistors, metal oxide film resistors, chemical deposition film resistors, glass glaze film resistors, metal nitride film resistors.
3. Solid resistors: inorganic synthetic solid carbon resistors, organic synthetic solid carbon resistors. 4. Sensitive resistors
: varistors, thermistors, photoresistors, force-sensitive resistors, gas-sensitive resistors, and humidity-sensitive resistors.
3. Main characteristic parameters
1. Nominal resistance: the resistance indicated on the resistor.
2. Allowable error: The percentage of the difference between the nominal resistance and the actual resistance and the nominal resistance is called the resistance deviation, which indicates the accuracy of the resistor.
The corresponding relationship between the allowable error and the accuracy level is as follows: ±0.5%-0.05, ±1%-0.1 (or 00), ±2%-0.2 (or 0), ±5%-level I, ±10%-level II, ±20%-level III
3. Rated power: The maximum power allowed to be dissipated by the resistor for long-term operation under normal atmospheric pressure of 90-106.6KPa and ambient temperature of -55℃～+70℃.
The rated power series of wirewound resistors are (W): 1/20, 1/8, 1/4, 1/2, 1, 2, 4, 8, 10, 16, 25, 40, 50, 75,
100, 150, 250, 500. The rated power series of non-wirewound resistors are (W): 1/20, 1/8, 1/4, 1/2, 1, 2,
5, 10, 25, 50, 100. 4. Rated voltage: The voltage converted from the resistance value and the rated power.
5. Maximum working voltage: The maximum continuous working voltage allowed. When working at low pressure, the maximum working voltage is lower.
6. Temperature coefficient: The relative change in resistance value caused by every 1°C change in temperature. The smaller the temperature coefficient, the better the stability of the resistor. The resistance value increases with the increase of temperature, which is a positive temperature coefficient, and vice versa, it is a negative temperature coefficient.
7. Aging coefficient: The percentage of relative change in resistance value of the resistor under long-term load of rated power. It is a parameter indicating the life of the resistor.
8. Voltage coefficient: The relative change of the resistor for every 1 volt change in voltage within the specified voltage range.
9. Noise: An irregular voltage fluctuation generated in the resistor, including thermal noise and current noise. Thermal noise is caused by the irregular free movement of electrons inside the conductor, which causes the voltage at any two points of the conductor to change irregularly. IV
. Resistor resistance marking method
1. Direct marking method: Use numbers and unit symbols to mark the resistance value on the surface of the resistor. The allowable error is directly expressed in percentage. If the deviation is not marked on the resistor, it is ±20%.
2. Text symbol method: Use a regular combination of Arabic numerals and text symbols to indicate the nominal resistance value, and the allowable deviation is also indicated by text symbols. The number before the symbol indicates the integer resistance value, and the number after it indicates the first decimal resistance value and the second decimal resistance value respectively.
Text symbols indicating allowable error
Text symbol DFGJKM
Allowable deviation ±0.5% ±1% ±2% ±5% ±10% ±20%
3. Digital method: A marking method that uses three digits to indicate the nominal value on the resistor. From left to right, the first and second digits are effective values, and the third digit is the exponent, that is, the number of zeros, in ohms. Deviations are usually expressed in text symbols.
4. Color code method: Use different colored strips or dots to mark the nominal resistance and allowable deviation on the surface of the resistor. Most foreign resistors use the color code method.
Black-0, brown-1, red-2, orange-3, yellow-4, green-5, blue-6, purple-7, gray-8, white-9, gold-±5%, silver-±10%, colorless-±20%
When the resistor has four rings, the last ring must be gold or silver, the first two digits are effective digits, the third digit is the exponent, and the fourth digit is the deviation. When the resistor has five rings, the last ring is farther away from the previous four rings. The first three digits are effective digits, the fourth digit is the exponent, and the fifth digit is the deviation.
V. Commonly used resistors
1. Potentiometers Potentiometers
are electromechanical components that use the sliding of the brush on the resistor body to obtain an output voltage that is related to the displacement of the brush.
1.1 Synthetic carbon film potentiometer
The resistor body is made of ground carbon black, graphite, quartz and other materials coated on the surface of the substrate. The process is simple and it is the most widely used potentiometer at present. The characteristics are high resolution, good wear resistance and long life. The disadvantages are current noise, large nonlinearity, poor moisture resistance and resistance stability.
1.2 Organic solid potentiometer
The organic solid potentiometer is a new type of potentiometer. It uses the method of heating and plastic pressing to press the organic resistor powder into the groove of the insulator. Compared with the carbon film potentiometer, the organic solid potentiometer has the advantages of good heat resistance, high power, high reliability and good wear resistance. However, it has a large temperature coefficient, large dynamic noise, poor moisture resistance, complex manufacturing process and poor resistance accuracy. It is used to adjust voltage and current in miniaturized, highly reliable and highly wear-resistant electronic equipment and AC and DC circuits.
1.3 Metal glass uranium potentiometer
The metal glass uranium resistor slurry is coated on the ceramic substrate according to a certain pattern by screen printing, and then sintered at high temperature. The characteristics are: wide resistance range, good heat resistance, strong overload capacity, moisture resistance, wear resistance, etc. It is a very promising potentiometer variety. The disadvantages are large contact resistance and current noise.
1.4 Wire Wound Potentiometer
The wire wound potentiometer is made by using constantan wire or nickel-chromium alloy wire as the resistor body and winding it on an insulating skeleton. The characteristics of the wire wound potentiometer are small contact resistance, high precision, and small temperature coefficient. Its disadvantages are poor resolution, low resistance, and poor high-frequency characteristics. It is mainly used as a voltage divider, a rheostat, zero adjustment and working point in instruments, etc.
1.5 Metal Film Potentiometer
The resistor body of the metal film potentiometer can be composed of alloy film, metal oxide film, metal foil, etc. It is characterized by high resolution, high temperature resistance, small temperature coefficient, small dynamic noise, and good smoothness.
1.6 Conductive plastic potentiometer
Use a special process to coat DAP (dipropylene phthalate) resistor paste on the insulating body, heat and polymerize it into a resistor film, or heat and press DAP resistor powder into the groove of the insulating substrate to form a solid body as a resistor body. Features: good smoothness, excellent resolution, good wear resistance, long life, low dynamic noise, high reliability, and chemical corrosion resistance. Used in servo systems of space devices, missiles, and aircraft radar antennas.
1.7 Potentiometer with switch
There are rotary switch potentiometers, push-pull switch potentiometers, and push-push switch potentiometers .
1.8 Pre-adjusted potentiometers
Once the pre-adjusted potentiometer is debugged in the circuit, the adjustment position is sealed with wax and it is no longer adjusted under normal circumstances.
1.9 Direct slide potentiometer
The resistance value is changed by direct sliding.
1.10 Double-connected potentiometer
There are heteroaxial double-connected potentiometers and coaxial double-connected potentiometers.
1.11 Contactless potentiometer
Contactless potentiometers eliminate mechanical contact, have long life and high reliability, and are divided into photoelectric potentiometers, magnetic sensitive potentiometers, etc.
2. Solid carbon resistor
A solid resistor is made by mixing carbonaceous particles, strong conductive materials, fillers and adhesives.
Features: low price, but its resistance error and noise voltage are large, and its stability is poor. It is rarely used at present. 3. Wirewound resistor It is made of high-resistance alloy wire wound on an insulating skeleton, and coated with a heat-resistant glaze insulation layer or insulating paint on the outside.
Wirewound resistors have a low temperature coefficient, high resistance accuracy, good stability, heat resistance and corrosion resistance. They are mainly used as precision high-power resistors. The disadvantages are poor high-frequency performance and large time constant. 4. Thin film resistor It is made by evaporating a certain resistivity material on the surface of an insulating material. The main ones are as follows: 4.1 Carbon film resistor Made by depositing crystalline carbon on a ceramic rod skeleton. Carbon film resistors are low in cost, stable in performance, wide in resistance range, low in temperature coefficient and voltage coefficient, and are currently the most widely used resistors. 4.2 Metal film resistors. Alloy materials are deposited on the surface of the ceramic rod skeleton by vacuum evaporation. Metal film resistors have higher precision, better stability, lower noise, and lower temperature coefficient than carbon film resistors. They are widely used in instruments and communication equipment. 4.3 Metal oxide film resistor A layer of metal oxide is deposited on an insulating rod. Since it is an oxide itself, it is stable at high temperatures, resistant to heat shock, and has strong load capacity. 4.4 Synthetic film resistor It is obtained by applying a conductive composite suspension on a substrate, so it is also called a paint film resistor. Since its conductive layer has a granular structure, it has high noise and low precision. It is mainly used to make high-voltage, high-resistance, and small resistors. 5. Metal glass uranium resistor Mix metal powder and glass uranium powder and print them on the substrate using screen printing. Moisture resistant, high temperature, small temperature coefficient, mainly used in thick film circuits. 6. SMT chip resistors are a form of metal glass uranium resistors. Its resistor body is made of highly reliable ruthenium series glass uranium materials sintered at high temperature, and the electrodes are made of silver-palladium alloy paste. Small size, high precision, good stability, because it is a sheet component, so the high-frequency performance is good. 7. Sensitive resistors Sensitive resistors refer to resistors whose device characteristics are sensitive to temperature, voltage, humidity, light, gas, magnetic field, pressure, etc. The symbol of the sensitive resistor is to add a slash to the symbol of the ordinary resistor, and mark the type of sensitive resistor next to it, such as: t. v, etc. 7.1. Varistor Mainly silicon carbide and zinc oxide varistors, zinc oxide has more excellent characteristics. 7.2. Humidity-sensitive resistors Consists of a humidity-sensitive layer, an electrode, and an insulator. Humidity-sensitive resistors mainly include lithium chloride humidity-sensitive resistors, carbon humidity-sensitive resistors, and oxide humidity-sensitive resistors. The resistance of lithium chloride hygroresistors decreases as humidity increases. The disadvantages are that the test range is small, the characteristic repeatability is poor, and they are greatly affected by temperature. The disadvantages of carbon hygroresistors are that they have low sensitivity at low temperatures, the resistance is greatly affected by temperature, and they are rarely used due to their aging characteristics. Oxide hygroresistors have superior performance, can be used for a long time, are less affected by temperature, and the resistance is linearly related to humidity changes. There are tin oxide, nickel ferrite, and other materials. 7.3. Photoresistors Photoresistors are electronic components whose conductivity changes with the change of light intensity. When a certain substance is exposed to light, the concentration of carriers increases, thereby increasing the conductivity. This is the photoconductivity effect. 7.4. Gas-sensitive resistors They are made by using certain semiconductors to absorb certain gases and undergo redox reactions. The main components are metal oxides. The main varieties are: metal oxide gas-sensitive resistors, composite oxide gas-sensitive resistors, ceramic gas-sensitive resistors, etc. 7.5. Force-sensitive resistors Force-sensitive resistors are resistors whose resistance changes with pressure, and are called piezoresistors abroad. The so-called piezoresistance effect is the effect that the resistivity of semiconductor materials changes with mechanical stress. It can be made into various torque meters, semiconductor microphones, pressure sensors, etc. The main varieties are silicon force sensitive resistors and selenium tellurium alloy force sensitive resistors. Relatively speaking, alloy resistors have higher sensitivity. Basic knowledge of circuit design (2) - capacitors


































Capacitors are one of the electronic components used in large quantities in electronic devices. They are widely used in DC isolation, coupling, bypass, filtering, tuning circuits, energy conversion, control circuits, etc. C represents capacitance. The units of capacitance are Farad (F), microfarad (uF), and picofarad (pF). 1F=10^6uF=10^12pF.
1. Naming method of capacitor models
The model of domestic capacitors generally consists of four parts (not applicable to varistor, variable, and vacuum capacitors). They represent name, material, classification, and serial number respectively.
The first part: name, represented by letters, capacitors
are represented by C. The second part: materials, represented by letters.
The third part: classification, generally represented by numbers, and some are represented by letters.
The fourth part: serial number, represented by numbers.
The materials of the products are indicated by letters: A-tantalum electrolytic, B-polystyrene and other non-polar films, C-high-frequency ceramics, D-aluminum electrolytic, E-other material electrolytic, G-alloy electrolytic, H-composite dielectric, I-glass glaze, J-metallized paper, L-polyester and other polar organic films, N-niobium electrolytic, O-glass film, Q-paint film, T-low-frequency ceramics, V-mica paper, Y-mica, Z-paper dielectric

2. Classification of capacitors According to the structure, they are divided into three categories: fixed capacitors, variable capacitors and fine-tuning capacitors. According to the electrolyte, they are divided into: organic dielectric capacitors, inorganic dielectric capacitors, electrolytic capacitors and air dielectric capacitors, etc. According to the purpose, they are divided into: high-frequency bypass, low-frequency bypass, filtering, tuning, high-frequency coupling, low-frequency coupling, and small capacitors. High-frequency bypass: ceramic capacitors, mica capacitors, glass film capacitors, polyester capacitors, and glass glaze capacitors. Low-frequency bypass: paper dielectric capacitors, ceramic capacitors, aluminum electrolytic capacitors, and polyester capacitors. Filtering: aluminum electrolytic capacitors, paper dielectric capacitors, composite paper dielectric capacitors, and liquid tantalum capacitors. Tuning: ceramic capacitors, mica capacitors, glass film capacitors, and polystyrene capacitors. High-frequency coupling: ceramic capacitors, mica capacitors, and polystyrene capacitors. Low-frequency coupling: paper dielectric capacitors, ceramic capacitors, aluminum electrolytic capacitors, polyester capacitors, and solid tantalum capacitors. Small capacitors: metallized paper dielectric capacitors, ceramic capacitors, aluminum electrolytic capacitors, polystyrene capacitors, solid tantalum capacitors, glass glaze capacitors, metallized polyester capacitors, polypropylene capacitors, and mica capacitors.

3. Commonly used capacitors 1. Aluminum electrolytic capacitors A capacitor made of absorbent paper soaked in a paste electrolyte sandwiched between two aluminum foils, with a thin oxide film as the dielectric. Because the oxide film has a unidirectional conductive property, the electrolytic capacitor has polarity. Large capacity, can withstand large pulsating currents, large capacity errors, and large leakage currents; ordinary ones are not suitable for high-frequency and low-temperature applications, and should not be used at frequencies above 25kHz, low-frequency bypass, signal coupling, and power supply filtering. 2. Tantalum electrolytic capacitors Sintered tantalum blocks are used as positive electrodes, and solid manganese dioxide is used as electrolyte. The temperature characteristics, frequency characteristics, and reliability are better than ordinary electrolytic capacitors, especially the leakage current is extremely small, the storage is good, the life is long, the capacity error is small, and the volume is small. The maximum capacitance-voltage product can be obtained per unit volume. The tolerance to pulsating current is poor, and if damaged, it is easy to short-circuit. Ultra-small and highly reliable parts 3. Film capacitors The structure is similar to that of paper capacitors, but polyester, polystyrene and other low-loss plastic materials are used as dielectrics. The frequency characteristics are good, the dielectric loss is small, and it cannot be made into a large capacity. The heat resistance is poor. Filters, integration, oscillation, timing circuits 4. Ceramic capacitors Through-core or pillar-type ceramic capacitors, one of its electrodes is the mounting screw. The lead inductance is extremely small, the frequency characteristics are good, the dielectric loss is small, and it has a temperature compensation effect. It cannot be made into a large capacity, and vibration will cause the capacity to change. It is particularly suitable for high-frequency bypass 5. Monolithic capacitors (multilayer ceramic capacitors) are coated with electrode paddle materials on several pieces of ceramic film blanks. After stacking, they are wound into an indivisible whole at one time, and then encapsulated with resin on the outside to form a new type of capacitor with small volume, large capacity, high reliability and high temperature resistance. Low-frequency monolithic capacitors with high dielectric constants also have stable performance, small size, high Q value, large capacity error, noise bypass, filter, integration, oscillation circuit 6. Paper capacitors Generally, two aluminum foils are used as electrodes, separated by capacitor paper with a thickness of 0.008-0.012mm in the middle and wound in an overlapping manner. The manufacturing process is simple, the price is cheap, and a large capacitance can be obtained. Generally, it cannot be used at a frequency higher than 3-4MHz in low-frequency circuits. The withstand voltage of oil-immersed capacitors is higher than that of ordinary paper capacitors, and the stability is also good. It is suitable for high-voltage circuits. 7. Fine-tuning capacitors. The capacitance can be adjusted within a small range and can be fixed to a certain capacitance value after adjustment. The Q value of ceramic fine-tuning capacitors is high and the volume is small. They can usually be divided into two types: round tube type and round disc type. 8. Mica and polystyrene dielectrics usually use spring-type, which has a simple structure but poor stability. Wirewound ceramic fine-tuning capacitors change the capacitance by removing copper wire (external electrode), so the capacitance can only be reduced, which is not suitable for use in occasions that require repeated debugging. 9. Ceramic capacitors. The capacitor ceramic (barium titanate monoxide) with high dielectric constant is extruded into round tubes, round discs or discs as the medium, and silver is plated on the ceramic as the electrode by sintering. It is divided into high-frequency ceramic dielectric and low-frequency ceramic dielectric. Capacitors with small positive capacitance temperature coefficient are used in high-stability oscillation circuits as loop capacitors and pad capacitors. Low-frequency ceramic capacitors are limited to bypass or DC isolation in circuits with low operating frequencies, or in places where stability and loss are not required (including high frequencies). This type of capacitor is not suitable for use in pulse circuits because they are easily broken down by pulse voltages. High-frequency ceramic capacitors are suitable for high-frequency circuits. Mica capacitors can be divided into foil type and silver-coated type in terms of structure. The silver-coated electrode is made by directly plating a silver layer on the mica sheet by vacuum evaporation or sintering. Since the air gap is eliminated, the temperature coefficient is greatly reduced, and the capacitance stability is also higher than that of the foil type. Good frequency characteristics, high Q value, small temperature coefficient, can not be made into large capacity, widely used in high-frequency electrical appliances, and can be used as standard capacitors 10. Glass glaze capacitors are made of a special mixture with a concentration suitable for spraying sprayed into a thin film, and the dielectric is sintered with a silver layer electrode to form a "monolithic" structure. The performance is comparable to that of mica capacitors, and can withstand various climate environments. It can generally work at 200°C or higher temperatures, with a rated working voltage of up to 500V, and a loss tgδ0.0005～0.008

4. Main characteristic parameters of capacitors: 1. Nominal capacitance and allowable deviation The nominal capacitance is the capacitance marked on the capacitor. The deviation between the actual capacitance of the capacitor and the nominal capacitance is called error, and the deviation within the allowable range is called accuracy. The corresponding relationship between the accuracy level and the allowable error: 00 (01) - ±1%, 0 (02) - ±2%, Ⅰ - ±5%, Ⅱ - ±10%, Ⅲ - ±20%, Ⅳ - (+20% -10%), Ⅴ - (+50% -20%), Ⅵ - (+50% -30%). Generally, capacitors are usually used in grades Ⅰ, Ⅱ, and Ⅲ, and electrolytic capacitors are used in grades Ⅳ, Ⅴ, and Ⅵ, which are selected according to the purpose. 2. Rated voltage The maximum effective value of the DC voltage that can be continuously applied to the capacitor at the lowest ambient temperature and the rated ambient temperature is generally marked directly on the capacitor casing. If the working voltage exceeds the withstand voltage of the capacitor, the capacitor will break down, causing irreparable permanent damage. 3. Insulation resistance When a DC voltage is applied to a capacitor, a leakage current is generated. The ratio of the two is called insulation resistance. When the capacitance is small, it mainly depends on the surface state of the capacitor. When the capacitance is greater than 0.1uf, it mainly depends on the performance of the dielectric. The smaller the insulation resistance, the better. Capacitor time constant: In order to properly evaluate the insulation of large-capacity capacitors, a time constant is introduced. It is equal to the product of the insulation resistance and the capacitance of the capacitor. 4. Loss The energy consumed by a capacitor due to heat generation per unit time under the action of an electric field is called loss. All types of capacitors have specified their allowable loss values ​​within a certain frequency range. The loss of a capacitor is mainly caused by dielectric loss, conductivity loss and the resistance of all metal parts of the capacitor. Under the action of a DC electric field, the loss of a capacitor exists in the form of leakage conduction loss, which is generally small. Under the action of an alternating electric field, the loss of a capacitor is not only related to leakage conduction, but also to the periodic polarization establishment process.

5. Frequency characteristics
As the frequency increases, the capacitance of a general capacitor tends to decrease.

5. Capacitor Capacitance Marking 1. Direct Marking Method Use numbers and unit symbols to mark directly. For example, 01uF means 0.01 microfarads. Some capacitors use "R" to indicate the decimal point, such as R56 for 0.56 microfarads. 2. Text Symbol Method Use a regular combination of numbers and text symbols to indicate the capacity. For example, p10 means 0.1pF, 1p0 means 1pF, 6P8 means 6.8pF, and 2u2 means 2.2uF. 3. Color Code Method Use color rings or color dots to indicate the main parameters of the capacitor. The color code method of capacitors is the same as that of resistors. Capacitor deviation symbol: +100%-0--H, +100%-10%--R, +50%-10%--T, +30%-10%--Q, +50%-20%--S, +80%-20%--Z. Basic knowledge of circuit design (3) - Inductor Coil Inductor coil is made of wire wound around an insulating tube in turns. The wires are insulated from each other, and the insulating tube can be hollow or contain an iron core or a magnetic powder core. It is referred to as inductor. It is represented by L, and the units are Henry (H), millihenry (mH), and microhenry (uH). 1H=10^3mH=10^6uH. 1. Classification of inductors Classification by inductance form: fixed inductance, variable inductance. Classification by magnetic conductor properties: air core coil, ferrite coil, iron core coil, copper core coil. Classification by working properties: antenna coil, oscillation coil, choke coil, trap coil, deflection coil. Classification by winding structure: single-layer coil, multi-layer coil, honeycomb coil. 2. Main characteristic parameters of inductor coil 1. Inductance L Inductance L represents the inherent characteristics of the coil itself and has nothing to do with the current. Except for special inductor coils (color-coded inductors), the inductance is generally not specifically marked on the coil, but marked with a specific name. 2. Inductive reactance XL The magnitude of the inductive coil's resistance to AC current is called inductive reactance XL, and its unit is ohm. Its relationship with inductance L and AC frequency f is XL=2πfL 3. Quality factor Q The quality factor Q is a physical quantity that represents the quality of the coil. Q is the ratio of the inductive reactance XL to its equivalent resistance, that is, Q=XL/R The higher the Q value of the coil, the smaller the loss of the loop. The Q value of the coil is related to factors such as the DC resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shielding cover or the iron core, and the influence of the high-frequency skin effect. The Q value of the coil is usually tens to hundreds. 4. Distributed capacitance The capacitance between turns of the coil, between the coil and the shielding cover, and between the coil and the bottom plate is called distributed capacitance. The existence of distributed capacitance reduces the Q value of the coil and deteriorates its stability, so the smaller the distributed capacitance of the coil, the better. III. Commonly used coils 1. Single-layer coils Single-layer coils are insulated wires wound around a paper tube or bakelite skeleton in circles. Such as the medium wave antenna coil of a transistor radio. 2. Honeycomb coil If the plane of the wound coil is not parallel to the rotating plane, but intersects at a certain angle, this coil is called a honeycomb coil. The number of times the wire bends back and forth during one rotation is often called the number of inflection points. The advantages of honeycomb winding are small size, small distributed capacitance, and large inductance. Honeycomb coils are all wound using honeycomb winding machines. The more inflection points, the smaller the distributed capacitance. 3. Ferrite core and iron powder core coils The inductance of the coil is related to whether there is a magnetic core. Inserting a ferrite core into an air-core coil can increase the inductance and improve the quality factor of the coil. 4. Copper core coil Copper core coils are widely used in the ultra-short wave range. The position of the rotating copper core in the coil is used to change the inductance. This adjustment is more convenient and durable. 5. Color-coded inductors Color-coded inductors are inductors with fixed inductance. The inductance marking method is the same as that of resistors, marked with color rings. 6. Choke coil: The coil that limits the passage of alternating current is called a choke coil, which is divided into high-frequency choke coil and low-frequency choke coil. 7. Deflection coil: The deflection coil is the load of the output stage of the TV scanning circuit. The deflection coil requires: high deflection sensitivity, uniform magnetic field, high Q value, small size and low price. Transformer : The transformer is a device that converts AC voltage, current and impedance. When AC current passes through the primary coil, AC magnetic flux is generated in the iron core (or magnetic core), which induces voltage (or current) in the secondary coil. The transformer consists of an iron core (or magnetic core) and a coil. The coil has two or more windings, of which the winding connected to the power supply is called the primary coil, and the remaining windings are called secondary coils. 1. Classification: Classification by cooling method: dry-type (self-cooling) transformer, oil-immersed (self-cooling) transformer, fluoride (evaporative cooling) transformer. Classification by moisture-proof method: open transformer, potted transformer, sealed transformer. Classification by core or coil structure: core transformer (tab core, C-type core, ferrite core), shell transformer (tab core, C-type core, ferrite core), toroidal transformer, metal foil transformer. Classification by power phase number: single-phase transformer, three-phase transformer, multi-phase transformer. Classification by use: power transformer, voltage regulating transformer, audio transformer, medium frequency transformer, high frequency transformer, pulse transformer. 2. Characteristic parameters of power transformer 1. Working frequency The core loss of the transformer is closely related to the frequency, so it should be designed and used according to the frequency of use. This frequency is called the working frequency. 2. Rated power Under the specified frequency and voltage, the transformer can work for a long time without exceeding the output power of the specified temperature rise. 3. Rated voltage Refers to the voltage allowed to be applied to the coil of the transformer, which shall not be greater than the specified value during operation. 4. Voltage ratio Refers to the ratio of the primary voltage to the secondary voltage of the transformer. There is a difference between the no-load voltage ratio and the load voltage ratio. 5. No-load current

























































When the secondary of the transformer is open, there is still a certain current in the primary, which is called the no-load current. The no-load current consists of the magnetizing current (generating magnetic flux) and the iron loss current (caused by the core loss). For a 50Hz power transformer, the no-load current is basically equal to the magnetizing current.
6 No-load loss: refers to the power loss measured in the primary when the secondary of the transformer is open. The main loss is the core loss, followed by the loss (copper loss) caused by the no-load current on the copper resistance of the primary coil, which is very small.
7 Efficiency
Refers to the percentage of the ratio of the secondary power P2 to the primary power P1. Generally, the larger the rated power of the transformer, the higher the efficiency.
8 Insulation resistance
Indicates the insulation performance between the coils of the transformer and between the coils and the core. The insulation resistance is related to the performance of the insulation material used, the temperature and humidity.
III. Characteristic parameters of audio transformers and high-frequency transformers
1 Frequency response
Refers to the characteristics of the transformer secondary output voltage changing with the operating frequency.
2 Passband
If the output voltage of the transformer at the intermediate frequency is U0, the frequency range when the output voltage (input voltage remains unchanged) drops to 0.707U0 is called the passband B of the transformer.
3 Primary-secondary impedance ratio
The primary and secondary of the transformer are connected to appropriate impedances Ro and Ri to match the primary and secondary impedances of the transformer. The ratio of Ro and Ri is called the primary-secondary impedance ratio. Under impedance matching, the transformer works in the best state and has the highest transmission efficiency.

Basic knowledge of circuit design (II)
1. Chinese semiconductor device model naming method
The semiconductor device model consists of five parts (field effect devices, special semiconductor devices, composite tubes, PIN tubes, and laser devices have only the third, fourth, and fifth parts). The meanings of the five parts are as follows:
Part 1: Use numbers to indicate the number of effective electrodes of semiconductor devices. 2-Diode, 3-Triode
Part 2: Use Chinese pinyin letters to indicate the material and polarity of semiconductor devices. When indicating diodes: AN type germanium material, BP type germanium material, CN type silicon material, DP type silicon material. When indicating triodes: A-PNP type germanium material, B-NPN type germanium material, C-PNP type silicon material, D-NPN type silicon material.
Part 3: Use Chinese pinyin letters to indicate the internal type of semiconductor devices. P-ordinary tube, V-microwave tube, W-voltage regulator tube, C-parameter tube, Z-rectifier tube, L-rectifier stack, S-tunnel tube, N-damping tube, U-photoelectric device, K-switching tube, X-low-frequency low-power tube (F3MHz, Pc1W), A-high-frequency high-power tube (f>3MHz, Pc>1W), T-semiconductor thyristor (controlled rectifier), Y-body effect device, B-avalanche tube, J-step recovery tube, CS-field effect tube, BT-semiconductor special device, FH-composite tube, PIN-PIN type tube, JG-laser device.
Part 4: Use numbers to represent serial numbers
Part 5: Use Chinese pinyin letters to represent specification numbers
For example: 3DG18 represents NPN type silicon material high-frequency triode
Japanese semiconductor discrete device model naming method
2. Semiconductor discrete devices produced in Japan are composed of five to seven parts. Usually only the first five parts are used, and the meaning of the symbols of each part is as follows:
Part 1: Use numbers to indicate the number or type of effective electrodes of the device. 0-Photoelectric (i.e. photosensitive) diode triode and combination tube of the above devices, 1-diode, 2 triode or other devices with two pn junctions, 3-other devices with four effective electrodes or three pn junctions, ┄┄ and so on.
Part 2: Japan Electronics Industry Association JEIA registration mark. S-indicates semiconductor discrete devices registered with Japan Electronics Industry Association JEIA.
Part 3: Use letters to indicate the polarity and type of materials used in the device. A-PNP type high frequency tube, B-PNP type low frequency tube, C-NPN type high frequency tube, D-NPN type low frequency tube, FP control electrode thyristor, GN control electrode thyristor, HN base single junction transistor, JP channel field effect tube, KN channel field effect tube, M-bidirectional thyristor.
Part 4: Use numbers to indicate the serial number registered with Japan Electronics Industry Association JEIA. Integers with two or more digits - starting from "11", indicating the serial number registered with the Japan Electronics Industry Association (JEIA); devices with the same performance from different companies can use the same serial number; the larger the number, the more recent the product.
Part 5: Use letters to indicate the improved product mark of the same model. A, B, C, D, E, F indicate that this device is an improved product of the original model.
American semiconductor discrete device model naming method
3. The naming method of transistors or other semiconductor devices in the United States is relatively confusing. The naming method of semiconductor discrete devices of the American Electronics Industry Association is as follows:
Part 1: Use symbols to indicate the type of device use. JAN-military grade, JANTX-special military grade, JANTXV-super special military grade, JANS-aerospace grade, (none)-non-military products.
Part 2: Use numbers to indicate the number of pn junctions. 1-diode, 2=triode, 3-three pn junction devices, nn pn junction devices.
Part 3: American Electronics Industry Association (EIA) registration mark. N-The device has been registered with the American Electronics Industry Association (EIA).
Part 4: American Electronics Industry Association registration serial number. Multi-digit numbers - the serial number of the device registered with the American Electronics Industry Association.
Part 5: Use letters to indicate the device classification. A, B, C, D, ┄┄ - different grades of the same model device. For example: JAN2N3251A represents PNP silicon high-frequency low-power switching transistor, JAN-military grade, 2-transistor, N-EIA registration mark, 3251-EIA registration serial number, A-2N3251A grade.
4. International Electronics Federation Semiconductor Device Model Naming Method
Most European countries such as Germany, France, Italy, the Netherlands, Belgium, and Eastern European countries such as Hungary, Romania, Yugoslavia, and Poland use the International Electronics Federation semiconductor discrete device model naming method. This naming method consists of four basic parts, and the symbols and meanings of each part are as follows:
Part 1: Use letters to indicate the materials used in the device. A-device uses materials with a bandgap of Eg = 0.6~1.0eV, such as germanium, B-device uses materials with Eg = 1.0~1.3eV, such as silicon, C-device uses materials with Eg>1.3eV, such as gallium arsenide, D-device uses materials with Eg<0.6eV, such as indium antimonide, E-device uses composite materials and materials used in photovoltaic cells
Part II: Use letters to indicate the type and main characteristics of the device. A-detection switch mixer diode, B-variable capacitance diode, C-low frequency low power transistor, D-low frequency high power transistor, E-tunnel diode, F-high frequency low power transistor, G-composite device and other devices, H-magnetic sensitive diode, K-Hall element in open magnetic circuit, L-high frequency high power transistor, M-Hall element in closed magnetic circuit, P-photosensitive device, Q-light emitting device, R-low power thyristor, S-low power switch tube, T-high power thyristor, U-high power switch tube, X-multiplier diode, Y-rectifier diode, Z-voltage regulator diode.
Part 3: Use numbers or letters plus numbers to indicate the registration number. Three digits represent the registration number of general semiconductor devices, and one letter plus two digits represent the registration number of special semiconductor devices.
Part 4: Use letters to classify devices of the same type. A, B, C, D, E┄┄-a mark indicating that devices of the same model are classified according to a certain parameter.
In addition to the four basic parts, suffixes are sometimes added to distinguish characteristics or further classify. Common suffixes are as follows:
1. Suffix of the Zener diode model. The first part of the suffix is ​​a letter, indicating the allowable error range of the stable voltage value. The letters A, B, C, D, and E represent the allowable errors of ±1%, ±2%, ±5%, ±10%, and ±15%, respectively; the second part of the suffix is ​​a number, indicating the integer value of the nominal stable voltage; the third part of the suffix is ​​the letter V, which represents the decimal point. The number after the letter V is the decimal value of the nominal stable voltage of the Zener diode.
2. The suffix of the rectifier diode is a number, indicating the maximum reverse peak withstand voltage value of the device, in volts.
3. The suffix of the thyristor model is also a number, usually indicating the smaller voltage value of the maximum reverse peak withstand voltage value and the maximum reverse turn-off voltage.
For example: BDX51- represents NPN silicon low-frequency high-power transistor, and AF239S- represents PNP germanium high-frequency low-power transistor.
5. Model naming method of early European semiconductor discrete devices
Some European countries, such as Germany and the Netherlands, use the following naming method.
Part 1: O- indicates semiconductor devices
Part 2: A- diode, C- transistor, AP- photodiode, CP- phototransistor, AZ- voltage regulator, RP- photoelectric device.
Part 3: Multi-digit numbers- indicate the registration number of the device.
Part 4: A, B, C┄┄- indicate variant products of the same model device.
The Russian semiconductor device model naming method is rarely used and is not introduced here.
1. Semiconductor diode parameter symbols and their meanings
CT--- barrier capacitance
Cj--- junction (inter-electrode) capacitance, indicating the total capacitance of the germanium detector diode under the specified bias voltage at both ends of the diode
Cjv--- bias junction capacitance
Co--- zero bias capacitance
Cjo--- zero bias junction capacitance
Cjo/Cjn--- junction capacitance change
Cs--- shell capacitance or package capacitance
Ct--- total capacitance
CTV--- voltage temperature coefficient. The ratio of the relative change of the stable voltage to the absolute change of the ambient temperature under the test current.
CTC---Capacitance temperature coefficient
Cvn---Nominal capacitance
IF---Forward DC current (forward test current). The current passing through the inter-electrode of the germanium detector diode under the specified forward voltage VF; the maximum operating current (average value) allowed to pass continuously in a sine half-wave for silicon rectifiers and silicon stacks under specified conditions of use, and the maximum forward DC current allowed to pass through silicon switching diodes at rated power; the current given when measuring the forward electrical parameters of the voltage-stabilizing diode
IF (AV)---Forward average current
IFM (IM)---Forward peak current (maximum forward current). The maximum forward pulse current allowed to pass through the diode at rated power. Light-emitting diode limit current.
IH---Constant current, holding current.
Ii---Light-emitting diode starting current
IFRM---Forward repetitive peak current
IFSM---Forward non-repetitive peak current (surge current)
Io---Rectified current. The working current passing under the conditions of specified frequency and specified voltage in a specific circuit
IF(ov)---Forward overload current
IL---Photocurrent or current-regulating diode limit current
ID---Dark current
IB2---Base modulation current in a unijunction transistor
IEM---Emitter peak current
IEB10---Reverse current between the emitter and the first base in a double-base unijunction transistor
IEB20---Emitter current in a double-base unijunction transistor
ICM---Maximum output average current
IFMP---Forward pulse current
IP---Peak current
IV---Valley current
IGT---Thyristor gate trigger current
IGD---Thyristor gate non-trigger current
IGFM---Gate forward peak current
IR (AV)---Reverse average current
IR (In)---Reverse DC current (reverse leakage current). When measuring the reverse characteristics, the given reverse current; the current passing through the silicon stack when a reverse voltage of a specified value is applied in a half-sine wave resistive load circuit; the current passing through when a reverse working voltage VR is applied across the ends of a silicon switching diode; the leakage current generated by a Zener diode under a reverse voltage; the leakage current of a rectifier tube under the highest reverse working voltage of a half-sine wave.
IRM---Reverse peak current
IRR---Thyristor reverse repetitive average current
IDR---Thyristor off-state average repetitive current
IRRM---Reverse repetitive peak current
IRSM---Reverse non-repetitive peak current (reverse surge current)
Irp---Reverse recovery current
Iz---Stable voltage current (reverse test current). When testing reverse electrical parameters, the given reverse current
Izk---Zener tube knee current
IOM---Maximum forward (rectifier) ​​current. The maximum instantaneous forward current that can be sustained under specified conditions; the maximum operating current allowed to continuously pass through the germanium detector diode in a half-wave sine rectifier circuit with a resistive load;
IZSM---Zener diode surge current
; IZM---maximum zener current. The current allowed to pass through the Zener diode under maximum power dissipation
iF---total instantaneous forward current
iR---total instantaneous reverse current
ir---reverse recovery current
Iop---operating current
Is---stable current of the Zener diode
f---frequency
n---capacitance change index; capacitance ratio
Q--figure of merit (quality factor)
δvz---Zener diode voltage drift
di/dt---critical rate of rise of on-state current
dv/dt---critical rate of rise of on-state voltage
PB---pulse burnout power
PFT (AV)---forward conduction average power dissipation
PFTM---forward peak power dissipation
PFT---forward conduction total instantaneous power dissipation
Pd---dissipation power
PG---gate average
power PGM---gate peak power
PC--control electrode average power or collector dissipation power
Pi---input power
PK---maximum switching power
PM---Rated power. The maximum power that a silicon diode can withstand when the junction temperature is not higher than 150 degrees
PMP---Maximum leakage pulse power
PMS---Maximum withstand pulse power
Po---Output power
PR---Reverse surge power
Ptot---Total dissipated power
Pomax---Maximum output power
Psc---Continuous output power
PSM---Non-repetitive surge power
PZM---Maximum dissipated power. Under given conditions of use, the maximum power that a Zener diode is allowed to withstand
RF (r)---Forward differential resistance. When forward conduction occurs, the current increases with the voltage exponentially, showing obvious nonlinear characteristics. At a certain forward voltage, the voltage increases by a small amount △V, and the forward current increases accordingly △I, then △V/△I is called differential resistance
RBB---base resistance of dual base transistor
RE---RF resistance
RL---load resistance
Rs(rs)----series resistance
Rth----thermal resistance
R(th)ja----thermal resistance from junction to environment
Rz(ru)---dynamic resistance
R(th)jc---thermal resistance from junction to shell
r δ---attenuation resistance
r(th)---transient resistance
Ta---ambient temperature
Tc---case temperature
td---delay time
tf---fall time
tfr---forward recovery time
tg---circuit commutation turn-off time
tgt---gate control pole turn-on time
Tj---junction temperature
Tjm---maximum junction temperature
ton---turn -on time
toff---turn-off time
tr---rise time
trr---reverse recovery time
ts---storage time
tstg---storage temperature of temperature compensation diode
a---temperature coefficient
λp---peak wavelength of light emission
△ λ---spectral half width
η---voltage division ratio or efficiency of single junction transistor
VB---reverse peak breakdown voltage
Vc---rectified input voltage
VB2B1---base voltage
VBE10---emitter and first base reverse voltage
VEB---saturation voltage drop
VFM---maximum forward voltage drop (forward peak voltage)
VF---Forward voltage drop (forward DC voltage)
△VF---Forward voltage drop difference
VDRM---Off-state repetitive peak voltage
VGT---Gate trigger voltage VGD
---Gate non-trigger voltage
VGFM---Gate forward peak voltage
VGRM---Gate reverse peak voltage
VF (AV)---Forward average voltage
Vo---AC input voltage
VOM---Maximum output average voltage
Vop---Operating voltage
Vn---Center voltage
Vp---Peak voltage
VR---Reverse operating voltage (Reverse DC voltage)
VRM---Reverse peak voltage (Maximum test voltage)
V (BR)---Breakdown voltage
Vth---Valve voltage (Threshold voltage)
VRRM---Reverse repetitive peak voltage (Reverse surge voltage)
VRWM---Reverse operating peak voltage
V v---valley voltage
Vz---stable voltage
△Vz---voltage increment of the voltage regulation range
Vs---pass voltage (signal voltage) or current-stabilizing tube stable current voltage
av---voltage temperature coefficient
Vk---knee voltage (current-stabilizing diode)
VL ---limit voltage
2. Bipolar transistor parameter symbols and their meanings
Cc---collector capacitance
Ccb---collector-base capacitance
Cce---emitter grounding output capacitance
Ci---input capacitance
Cib---common base input capacitance
Cie---common emitter input capacitance
Cies---common emitter short-circuit input capacitance
Cieo---common emitter open-circuit input capacitance
Cn---neutralization capacitance (external circuit parameters)
Co---output capacitance
Cob---common base output capacitance In the base circuit, the output capacitance between the collector and the base
Coe---common emitter output capacitance
Coeo---common emitter open circuit output capacitance
Cre---common emitter feedback capacitance
Cic---collector junction barrier capacitance
CL---load capacitance (external circuit parameters)
Cp---Parallel capacitor (external circuit parameter)
BVcbo---Emitter open circuit, collector and base breakdown voltage
BVceo---Base open circuit, CE junction breakdown voltage
BVebo---Collector open circuit EB junction breakdown voltage
BVces---Base and emitter short circuit CE junction breakdown voltage
BV cer---Base and emitter connected in series with a resistor, CE junction breakdown voltage
D---Duty cycle
fT---Characteristic frequency
fmax---Maximum oscillation frequency. The operating frequency when the transistor power gain is equal to 1
hFE---Common emitter static current amplification factor
hIE---Common emitter static input impedance
hOE---Common emitter static output conductance
h RE---Common emitter static voltage feedback coefficienthie
---Common emitter small signal short-circuit input impedancehre
---Common emitter small signal open-circuit voltage feedback coefficienthfe
---Common emitter small signal short-circuit voltage amplification factorhoe
---Common emitter small signal open-circuit output admittanceIB
---Average value of base DC current or AC currentIc
---Average value of collector DC current or AC currentIE
---Average value of emitter DC current or AC currentIcbo
---Base is grounded, emitter is open to ground, and the reverse cut-off current between collector and base under the specified VCB reverse voltage conditionIceo
---Emitter is grounded, base is open to ground, and the reverse cut-off current between collector and emitter under the specified reverse voltage VCE condition The reverse cut-off current between the emitter
Iebo---the base is grounded, the collector is open to the ground, and under the specified reverse voltage VEB, the reverse cut-off current between the emitter and the base
Iceer---the series resistance R between the base and the emitter, when the voltage VCE between the collector and the emitter is the specified value, the reverse cut-off current between the collector and the emitter
Ices---the emitter is grounded, the base is short-circuited to the ground, and under the specified reverse voltage VCE, the reverse cut-off current between the collector and the emitter
Icex---the emitter is grounded, a specified bias is applied between the base and the emitter, and under the specified reverse bias VCE, the reverse cut-off current between the collector and the emitter
ICM---the maximum allowable collector current or the maximum average value of the AC current.
IBM---The maximum value of the DC current that can continuously pass through the base within the range of the allowable dissipation power of the collector, or the maximum average value of the AC
currentICMP---The maximum allowable pulse current of the collectorISB
---Secondary breakdown currentIAGC
---Forward automatic control currentPc
---Collector dissipation
powerPCM---The maximum allowable dissipation power of the collectorPi
---Input powerPo
---Output powerPosc ---
Oscillation powerPn
---Noise powerPtot
---Total dissipated powerESB
---Secondary breakdown energyrbb
''---Base extension resistance (base intrinsic resistance)
rbb''Cc---Base-collector time constant, that is, the product of the base extension resistance and the collector junction capacitancerie
---Emitter grounded, input resistance when the AC output is short-
circuitedroe---Emitter grounded, output resistance when the AC input is short-circuited measured under the conditions of specified VCE, Ic or IE, and frequencyRE
---External emitter resistance (external circuit parameter)
RB---External base resistance (external circuit parameter)
Rc ---External collector resistance (external circuit parameter)
RBE---External base-emitter resistance (external circuit parameter)
RL---Load resistance (external circuit parameter)
RG---Signal source internal resistance
Rth---Thermal resistance
Ta---Ambient temperature
Tc---Case temperature
Ts---Junction temperature
Tjm---Maximum allowable junction temperature
Tstg---Storage temperature
td----Delay time
tr---Rise time
ts---Storage time
tf---Fall time
ton---Turn-
on time toff---Turn-off time
VCB---Collector-base (DC) voltage
VCE---Collector-emitter (DC) voltage
VBE---Base emitter (DC) voltage VCBO---Base grounded, emitter open to ground, the highest withstand voltage VE
between collector and base under specified conditions
BO---base grounded, collector open to ground, the highest withstand voltage between emitter and base under specified conditions
VCEO---emitter grounded, base open to ground, the highest withstand voltage between collector and emitter under specified conditions
VCER---emitter grounded, resistor R connected in series between base and emitter, the highest withstand voltage between collector and emitter under specified conditions
VCES---emitter grounded, base short-circuited to ground, the highest withstand voltage between collector and emitter under specified conditions
VCEX---emitter grounded, specified bias voltage applied between base and emitter, the highest withstand voltage between collector and emitter under specified conditions
Vp---punch-through voltage.
VSB---secondary breakdown voltage
VBB---Base (DC) power supply voltage (external circuit parameter)
Vcc---Collector (DC) power supply voltage (external circuit parameter)
VEE---Emitter (DC) power supply voltage (external circuit parameter)
VCE(sat)---Emitter grounded, collector-emitter saturation voltage drop under specified Ic and IB conditions
VBE(sat)---Emitter grounded, base-emitter saturation voltage drop (forward voltage drop) under specified Ic and IB conditions
VAGC---Forward automatic gain control voltage
Vn(pp)---Equivalent noise voltage peak value at input end
V n---Noise voltage
Cj---Junction (inter-electrode) capacitance, indicating the total capacitance of the germanium detector diode when a specified bias is applied to both ends of the diode
Cjv---Bias junction capacitance
Co---Zero bias capacitance
Cjo---Zero bias junction capacitance
Cjo/Cjn---Junction capacitance change
Cs---Case capacitance or package capacitance
Ct---Total capacitance
CTV---Voltage temperature coefficient. The ratio of the relative change of the stable voltage to the absolute change of the ambient temperature under the test current.
CTC---Capacitance temperature coefficient
Cvn---Nominal capacitance
IF---Forward DC current (forward test current). The current passing through the inter-electrode of the germanium detector diode under the specified forward voltage VF; the maximum operating current (average value) allowed to pass continuously in a sine half-wave for silicon rectifiers and silicon stacks under specified conditions of use, and the maximum forward DC current allowed to pass through silicon switching diodes at rated power; the current given when measuring the forward electrical parameters of the voltage-stabilizing diode
IF (AV)---Forward average current
IFM (IM)---Forward peak current (maximum forward current). The maximum forward pulse current allowed to pass through the diode at rated power. Light-emitting diode limit current.
IH---Constant current, holding current.
Ii---Light-emitting diode starting current
IFRM---Forward repetitive peak current
IFSM---Forward non-repetitive peak current (surge current)
Io---Rectified current. The working current passing under the conditions of specified frequency and specified voltage in a specific circuit
IF(ov)---Forward overload current
IL---Photocurrent or current-regulating diode limit current
ID---Dark current
IB2---Base modulation current in a unijunction transistor
IEM---Emitter peak current
IEB10---Reverse current between the emitter and the first base in a double-base unijunction transistor
IEB20---Emitter current in a double-base unijunction transistor
ICM---Maximum output average current
IFMP---Forward pulse current
IP---Peak current
IV---Valley current
IGT---Thyristor gate trigger current
IGD---Thyristor gate non-trigger current
IGFM---Gate forward peak current
IR (AV)---Reverse average current
IR (In)---Reverse DC current (reverse leakage current). When measuring the reverse characteristics, the given reverse current; the current passing through the silicon stack when a reverse voltage of a specified value is applied in a half-sine wave resistive load circuit; the current passing through when a reverse working voltage VR is applied across the ends of a silicon switching diode; the leakage current generated by a Zener diode under a reverse voltage; the leakage current of a rectifier tube under the highest reverse working voltage of a half-sine wave.
IRM---Reverse peak current
IRR---Thyristor reverse repetitive average current
IDR---Thyristor off-state average repetitive current
IRRM---Reverse repetitive peak current
IRSM---Reverse non-repetitive peak current (reverse surge current)
Irp---Reverse recovery current
Iz---Stable voltage current (reverse test current). When testing reverse electrical parameters, the given reverse current
Izk---Zener tube knee current
IOM---Maximum forward (rectifier) ​​current. The maximum instantaneous forward current that can be sustained under specified conditions; the maximum operating current allowed to continuously pass through the germanium detector diode in a half-wave sine rectifier circuit with a resistive load;
IZSM---Zener diode surge current
; IZM---maximum zener current. The current allowed to pass through the Zener diode under maximum power dissipation
iF---total instantaneous forward current
iR---total instantaneous reverse current
ir---reverse recovery current
Iop---operating current
Is---stable current of the Zener diode
f---frequency
n---capacitance change index; capacitance ratio
Q--figure of merit (quality factor)
δvz---Zener diode voltage drift
di/dt---critical rate of rise of on-state current
dv/dt---critical rate of rise of on-state voltage
PB---pulse burnout power
PFT (AV)---forward conduction average power dissipation
PFTM---forward peak power dissipation
PFT---forward conduction total instantaneous power dissipation
Pd---dissipation power
PG---gate average power
PGM---gate peak power
PC--control electrode average power or collector power dissipation
Pi---input power
PK---Maximum switching power
PM---Rated power. The maximum power that a silicon diode can withstand when the junction temperature is not higher than 150 degrees
PMP---Maximum leakage pulse power
PMS---Maximum withstand pulse power
Po---Output power
PR---Reverse surge power
Ptot---Total dissipated power
Pomax---Maximum output power
Psc---Continuous output power
PSM---Non-repetitive surge power
PZM---Maximum dissipated power. Under given conditions of use, the maximum power that a Zener diode is allowed to withstand
RF (r)---Forward differential resistance. When forward conduction occurs, the current increases with the voltage exponentially, showing obvious nonlinear characteristics. At a certain forward voltage, the voltage increases by a small amount △V, and the forward current increases accordingly △I, then △V/△I is called differential resistance
RBB---base resistance of dual base transistor
RE---RF resistance
RL---load resistance
Rs(rs)----series resistance
Rth----thermal resistance
R(th)ja----thermal resistance from junction to environment
Rz(ru)---dynamic resistance
R(th)jc---thermal resistance from junction to shell
r δ---attenuation resistance
r(th)---transient resistance
Ta---ambient temperature
Tc---case temperature
td---delay time
tf---fall time
tfr---forward recovery time
tg---circuit commutation turn-off time
tgt---gate control pole turn-on time
Tj---junction temperature
Tjm---maximum junction temperature
ton---turn-on time
toff---turn-off time
tr---rise time
trr---reverse recovery time
ts---storage time
tstg---storage temperature of temperature compensation diode
a---temperature coefficient
λp---peak wavelength of light emission
△ λ---spectral half width
η---voltage division ratio or efficiency of single junction transistor
VB---reverse peak breakdown voltage
Vc---rectified input voltage
VB2B1---base voltage
VBE10---emitter and first base reverse voltage
VEB---saturation voltage drop
VFM---maximum forward voltage drop (forward peak voltage)
VF---Forward voltage drop (forward DC voltage)
△VF---Forward voltage drop difference
VDRM---Off-state repetitive peak voltage
VGT---Gate trigger voltage VGD
---Gate non-trigger voltage
VGFM---Gate forward peak voltage
VGRM---Gate reverse peak voltage
VF (AV)---Forward average voltage
Vo---AC input voltage
VOM---Maximum output average voltage
Vop---Operating voltage
Vn---Center voltage
Vp---Peak voltage
VR---Reverse operating voltage (Reverse DC voltage)
VRM---Reverse peak voltage (Maximum test voltage)
V (BR)---Breakdown voltage
Vth---Valve voltage (Threshold voltage)
VRRM---Reverse repetitive peak voltage (Reverse surge voltage)
VRWM---Reverse operating peak voltage
V v---valley voltage
Vz---stable voltage
△Vz---voltage increment in the voltage range
Vs---pass voltage (signal voltage) or current-stabilizing diode stable current voltage
av---voltage temperature coefficient
Vk---knee voltage (current-stabilizing diode)
VL ---limit voltage
III. Meaning of field effect tube parameter symbols
Cds---drain-source capacitance
Cdu---drain-substrate capacitance
Cgd---gate-source capacitance
Cgs---drain-source capacitance
Ciss---gate short-circuit common source input capacitance
Coss---gate short-circuit common source output capacitance
Crss---gate short-circuit common source reverse transfer capacitance
D---duty cycle (duty cycle, external circuit parameter)
di/dt---current rise rate (external circuit parameter)
dv/dt---voltage rise rate (external circuit parameter)
ID---drain current (DC)
IDM---Drain pulse current
ID(on)---On-state drain current
IDQ---Quiet drain current (RF power tube)
IDS---Drain source current
IDSM---Maximum drain-source current
IDSS---Drain current when gate-source is short-circuited
IDS(sat)---Channel saturation current (drain-source saturation current)
IG---Gate current (DC)
IGF---Forward gate current
IGR---Reverse gate current
IGDO---Cut-off gate current when source is open
IGSO---Cut-off gate current when drain is open
IGM---Gate pulse current
IGP---Gate peak current
IF---Diode forward current
IGSS---Cut-off gate current when
drain is short-circuited IDSS1---Drain-source saturation current for the first tube
IDSS2---Drain-source saturation current for the second tube
Iu---Substrate current
Ipr---Current pulse peak (external circuit parameters)
gfs---forward transconductance
Gp---power gain
Gps---common source neutralization and high-frequency power gain
GpG---common gate neutralization and high-frequency power gain
GPD---common drain neutralization and high-frequency power gain
ggd---gate-drain conductance
gds---drain-source conductance
K---offset voltage temperature coefficient
Ku---transmission coefficient
L---load inductance (external circuit parameter)
LD---drain inductance
Ls---source inductance
rDS---drain-source resistance
rDS(on)---drain-source on-state resistance
rDS(of)---drain-source off-state resistance
rGD---gate-drain resistance
rGS---gate-source resistance
Rg---gate external resistance (external circuit parameter)
RL---load resistance (external circuit parameter)
R(th)jc---junction-to-case thermal resistance
R(th)ja---junction-to-ring thermal resistance
PD---drain power dissipation
PDM---maximum allowable drain power dissipation
PIN--input power
POUT---output power
PPK---pulse power peak value (external circuit parameters) to
(on)---turn-on delay time
td(off)---turn-off delay time
ti---rise
time ton
---turn-on time toff
---turn-off time tf---fall time
trr---reverse recovery time
Tj---junction temperature Tjm---maximum allowable junction temperature Ta---ambient temperature Tc---case temperature Tstg---storage temperature VDS---drain-source voltage (DC) VGS---gate-source voltage (DC) VGSF--forward gate-source voltage (DC) VGSR---reverse gate-source voltage (DC) VDD---drain (DC) power supply voltage (external circuit parameters) VGG---gate (DC) power supply voltage (external circuit parameter) Vss---source (DC) power supply voltage (external circuit parameter) VGS(th)---turn-on voltage or valve voltage V(BR)DSS---drain-source breakdown voltage V(BR)GSS---gate-source breakdown voltage when drain-source is short-circuited VDS(on)---drain-source on-state voltage VDS(sat)---drain-source saturation voltage VGD---gate-drain voltage (DC) Vsu---source-substrate voltage (DC) VDu---drain-substrate voltage (DC) VGu---gate-substrate voltage (DC) Zo---driving source internal resistance η---drain efficiency (RF power tube) Vn---noise voltage aID---drain current temperature coefficient ards---drain-source resistance temperature coefficient Basic knowledge of circuit design (5) - relay

1. Working principle and characteristics of relays Relay is an electronic control device, which has a control system (also known as input circuit) and a controlled system (also known as output circuit). It is usually used in automatic control circuits. It is actually an "automatic switch" that uses a smaller current to control a larger current. Therefore, it plays the role of automatic adjustment, safety protection, and circuit conversion in the circuit. 1. Working principle and characteristics of electromagnetic relays Electromagnetic relays are generally composed of iron core, coil, armature, contact spring, etc. As long as a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, thereby generating an electromagnetic effect. The armature will overcome the pulling force of the return spring under the action of electromagnetic attraction and be attracted to the iron core, thereby driving the moving contact of the armature to close with the static contact (normally open contact). When the coil is powered off, the electromagnetic attraction disappears, and the armature will return to its original position under the reaction force of the spring, so that the moving contact and the original static contact (normally closed contact) are attracted. In this way, the attraction and release achieve the purpose of conduction and disconnection in the circuit. The "normally open and normally closed" contacts of the relay can be distinguished as follows: the static contact in the disconnected state when the relay coil is not energized is called the "normally open contact"; the static contact in the connected state is called the "normally closed contact". 2. Working principle and characteristics of thermal reed relays The thermal reed relay is a new type of thermal switch that uses thermal magnetic materials to detect and control temperature. It consists of a temperature-sensitive magnetic ring, a constant magnetic ring, a reed switch, a heat-conducting mounting sheet, a plastic substrate and some other accessories. The thermal reed relay does not use coil excitation, but the magnetic force generated by the constant magnetic ring drives the switch action. Whether the constant magnetic ring can provide magnetic force to the reed switch is determined by the temperature control characteristics of the temperature-sensitive magnetic ring. 3. Working principle and characteristics of solid-state relays (SSRs) Solid-state relays are four-terminal devices with two terminals as input terminals and the other two terminals as output terminals. Isolation devices are used in the middle to achieve electrical isolation of input and output. Solid-state relays can be divided into AC and DC types according to the type of load power supply. According to the switch type, they can be divided into normally open and normally closed types. According to the isolation type, it can be divided into hybrid type, transformer isolation type and photoelectric isolation type, with photoelectric isolation type being the most common. .2. Main product technical parameters of relays 1. Rated working voltage Refers to the voltage required by the coil when the relay is working normally. Depending on the model of the relay, it can be AC ​​voltage or DC voltage. 2. DC resistance Refers to the DC resistance of the coil in the relay, which can be measured by a multimeter. 3. Pull-in current Refers to the minimum current that the relay can produce a pull-in action. In normal use, the given current must be slightly larger than the pull-in current so that the relay can work stably. As for the working voltage applied to the coil, it should generally not exceed 1.5 times the rated working voltage, otherwise a large current will be generated and the coil will be burned. 4. Release current Refers to the maximum current that the relay produces a release action. When the current in the pull-in state of the relay decreases to a certain extent, the relay will return to the unpowered release state. The current at this time is much smaller than the pull-in current. 5. Contact switching voltage and current Refers to the voltage and current that the relay is allowed to load. It determines the magnitude of voltage and current that the relay can control. This value should not be exceeded during use, otherwise the contacts of the relay will be easily damaged. 3. Relay test 1. Measure contact resistance Use the resistance range of the multimeter to measure the resistance between the normally closed contact and the moving point. The resistance should be 0; while the resistance between the normally open contact and the moving point is infinite. This can distinguish which is the normally closed contact and which is the normally open contact. 2. Measure coil resistance The resistance of the relay coil can be measured with the multimeter R×10Ω range to determine whether the coil has an open circuit. 3. Measure the pull-in voltage and pull-in current Find an adjustable voltage-stabilized power supply and an ammeter, input a set of voltages to the relay, and connect an ammeter in series in the power supply circuit for monitoring. Slowly increase the power supply voltage. When you hear the relay pull-in sound, write down the pull-in voltage and pull-in current. For accuracy, you can try several times and calculate the average value. 4. Measure the release voltage and release current Also connect and test as described above. After the relay is energized, gradually reduce the supply voltage. When you hear the relay release sound again, write down the voltage and current at this time. You can also try several times to obtain the average release voltage and release current. Under normal circumstances, the release voltage of the relay is about 10~50% of the pull-in voltage. If the release voltage is too small (less than 1/10 of the pull-in voltage), it cannot be used normally, which will threaten the stability of the circuit and work unsafely. 4. Electrical symbols and contact forms of relays The relay coil is represented by a rectangular symbol in the circuit. If the relay has two coils, draw two parallel rectangular boxes. At the same time, mark the text symbol "J" of the relay in or next to the rectangular box. There are two ways to represent the contacts of the relay: one is to draw them directly on one side of the rectangular box, which is more intuitive. The other is to draw each contact into its own control circuit according to the needs of circuit connection. Usually, the same text symbols are marked next to the contacts and coils of the same relay, and the contact groups are numbered to distinguish them. There are three basic forms of relay contacts: 1. Dynamic closing type (H type) When the coil is not energized, the two contacts are disconnected. After energization, the two contacts are closed. It is represented by the pinyin prefix "H" of the word "合". 2. Dynamic breaking type (D type) When the coil is not energized, the two contacts are closed. After energization, the two contacts are disconnected. It is represented by the pinyin prefix "D" of the word "断". 3. Conversion type (Z type) This is a contact group type. This contact group has three contacts, that is, the middle one is the moving contact, and the upper and lower ones are static contacts. When the coil is not energized, the moving contact and one of the static contacts are disconnected and the other is closed. After the coil is energized, the moving contact moves, making the originally disconnected one closed and the originally closed one disconnected, so as to achieve the purpose of conversion. Such a contact group is called a conversion contact. It is indicated by the pinyin prefix "z" of the word "转". 5. Selection of relays 1. First understand the necessary conditions: ① The power supply voltage of the control circuit and the maximum current it can provide; ② The voltage and current in the controlled circuit; ③ How many groups of contacts and what form the controlled circuit requires. When selecting relays, the power supply voltage of the general control circuit can be used as the basis for selection. The control circuit should be able to provide sufficient working current to the relay, otherwise the relay will be unstable when it is closed. 2. After consulting relevant information to determine the conditions of use, you can look up relevant information to find out the model and specification number of the required relay. If you already have a relay on hand, you can check whether it can be used based on the information. Finally, consider whether the size is appropriate. 3. Pay attention to the volume of the appliance. If it is used for general electrical appliances, in addition to considering the chassis volume, small relays mainly consider the circuit board installation layout. For small electrical appliances, such as toys and remote control devices, ultra-small relay products should be selected.