The resistance of electric conductors to current is called resistance, which is represented by the symbol R, and the unit is ohm, kiloohm, and megohm, which are denoted by Ω, KΩ, and MΩ, respectively.
1. The method of naming the resistance model:
The model of the domestic resistor is composed of four parts (not applicable to sensitive resistor)
The first part: the main title, represented by letters, which represents the name of the product. If R means resistance, W means potentiometer.
Part II: Materials, represented by letters, indicate what material the resistor 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 winding.
The third part: classification, generally expressed by numbers, and individual types are expressed by letters, indicating what type of products are. 1-ordinary, 2-ordinary, 3-ultra high frequency, 4-high resistance, 5-high temperature, 6-precision, 7-precision, 8-high pressure, 9-special, G-high power, T-adjustable.
The fourth part: serial number, expressed by numbers, indicating different varieties in the same product, to distinguish the appearance size and performance index of the product, etc.
For example: RT11 type ordinary carbon film resistor a1
Second, the classification of resistors
1. Wire wound resistors: general wire wound resistors, precision wire wound resistors, high power wire wound resistors, high frequency wire wound resistors.
2. Thin film resistors: carbon film resistors, synthetic carbon film resistors, metal film resistors, metal oxide film resistors, chemically deposited 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: varistor, thermistor, photoresistor, force-sensitive resistor, gas-sensitive resistor, humidity-sensitive resistor.
3. Main characteristic parameters
1. Nominal resistance: the resistance marked on the resistor.
2. Allowable error: The percentage of the difference between the nominal resistance value and the actual resistance value and the nominal resistance value is called the resistance deviation, which represents 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% -Ⅰ, ± 10% -Ⅱ, ± 20% -Ⅲ grade
3. Rated power: Under normal atmospheric pressure of 90-106.6KPa and ambient temperature of -55 ℃ ～ + 70 ℃, the maximum power allowed for long-term operation of the resistor.
The rated power series of wire wound resistors is (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-wire wound resistors is (W): 1/20, 1/8, 1/4, 1/2, 1, 2, 5, 10, 25, 50, 100
4. Rated voltage: voltage converted from resistance and rated power.
5. Maximum working voltage: The maximum allowable continuous working voltage. When working at low pressure, the maximum working voltage is lower.
6. Temperature coefficient: Relative change of resistance value caused by each temperature change of 1 ℃. The smaller the temperature coefficient, the better the stability of the resistor. The resistance increases with increasing temperature is the positive temperature coefficient, otherwise it is the negative temperature coefficient.
7. Aging coefficient: The percentage change in resistance of a resistor under a long-term load of rated power. It is a parameter indicating the length of life of the resistor.
8. Voltage coefficient: within the specified voltage range, the relative change of the resistor every time the voltage changes by 1 volt.
9. Noise: An irregular voltage fluctuation generated in the resistor, including two parts of thermal noise and current noise. Thermal noise is caused by the irregular free movement of electrons inside the conductor, which makes the voltage of any two points of the conductor irregular .
4. How to mark the resistance of resistors
1. Straight scale method: mark the resistance value on the surface of the resistor with numbers and unit symbols. The allowable error is directly expressed as a percentage. If there is no deviation on the resistor, it will be ± 20%.
2. Text symbol method: A regular combination of Arabic numerals and text symbols is used to represent the nominal resistance value, and its allowable deviation is also represented by text symbols. The number in front of the symbol represents the integer resistance, and the numbers after it represent the first decimal resistance and the second decimal resistance in turn.
Text symbol for allowable error
Text symbol DFGJKM
Allowable deviation ± 0.5% ± 1% ± 2% ± 5% ± 10% ± 20%
3. Digital method: A three-digit number on the resistor to indicate the nominal value. The numbers are from left to right, the first and second digits are valid values, and the third digit is the exponent, that is, the number of zeros, and the unit is Europe. Deviations are usually expressed in text symbols.
4. Color scale method: mark the nominal resistance and allowable deviation on the surface of the resistor with bands or dots of different colors. 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 resistance is four rings, the last ring must be gold or silver, the first two digits are valid digits, the third digit is the power, and the fourth digit is the deviation. When the resistance is five rings, the distance between the last ring and the previous four rings is larger. The first three digits are significant digits, the fourth digit is the power, and the fifth digit is the deviation.
5. Commonly used resistors
1. Potentiometer
The potentiometer is an electromechanical component. The sliding of the brush on the resistor body obtains an output voltage that has a certain relationship with the displacement of the brush.
1.1 Synthetic carbon film potentiometer
The resistor body is formed by coating carbon black, graphite, quartz and other materials on the surface of the substrate. The process is simple and is the most widely used potentiometer. It is characterized by high resolution, good wear resistance and long life. Disadvantages are current noise, large nonlinearity, poor humidity resistance and poor resistance stability.
1.2 Organic solid potentiometer
Organic solid potentiometer is a new type of potentiometer. It uses the method of heating and plastic pressing to press the organic resistance powder into the groove of the insulator. Compared with carbon membrane potentiometer, organic solid potentiometer has the advantages of good heat resistance, high power, high reliability and good wear resistance. However, the temperature coefficient is large, the dynamic noise is large, the moisture resistance is poor, the manufacturing process is complicated, and the resistance accuracy is poor. It is used to regulate voltage and current in miniaturized, highly reliable and wear-resistant electronic equipment and AC and DC circuits.
1.3 Metal glass uranium potentiometer
The metal glass uranium resistance paste is coated on the ceramic substrate according to a certain pattern by screen printing, and is sintered at high temperature. The characteristics are: wide resistance range, good heat resistance, strong overload capacity, moisture resistance, wear resistance, etc. are very promising types of potentiometers, the disadvantage is large contact resistance and current noise.
1.4 Wire wound potentiometer
The wire wound potentiometer is made of constantan wire or nickel-chromium alloy wire as a resistor and wound on an insulating skeleton. The characteristics of the winding potentiometer are small contact resistance, high accuracy, and small temperature coefficient. Its disadvantages are poor resolution, low resistance, and poor high-frequency characteristics. Mainly used as voltage divider, varistor, zero adjustment and working point in the instrument.
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. respectively. The characteristics are high resolution, high temperature resistance, small temperature coefficient, low dynamic noise and good smoothness.
1.6 Conductive plastic potentiometer
A special process is used to coat the DAP (dipropylene phthalate) resistance slurry on the insulation body, heat and polymerize it into a resistance film, or the solid body formed by pressing the DAP resistance powder in the groove of the insulation base as Resistor body. The characteristics are: good smoothness, excellent resolution, good wear resistance, long life, low dynamic noise, high reliability, and chemical resistance. Servo systems for space devices, missiles, aircraft radar antennas, etc.
1.7 Potentiometer with switch
Rotary switch potentiometer, push-pull switch potentiometer, push-push switch potentiometer
1.8 Pre-adjustable potentiometer
The pre-adjustable potentiometer is in the circuit. Once it is debugged, the adjustment position is sealed with wax, and it is no longer adjusted under normal circumstances.
1.9 Straight slide potentiometer
The resistance value is changed by a straight sliding method.
1.10 Double-connected potentiometer
There are coaxial double-connected potentiometer and coaxial double-connected potentiometer
1.11 Non-contact potentiometer
The non-contact potentiometer eliminates mechanical contact, has long life and high reliability, and is divided into photoelectric potentiometer and magnetosensitive potentiometer.
2. Solid core carbon resistor
A solid resistor is made by mixing carbonaceous particles, conductive material, filler and binder.
Features: low price, but its resistance error, noise voltage are large, and its stability is poor, so it is rarely used at present.
3. Winding resistors
It is made of high-resistance alloy wire wound on an insulating skeleton and coated with a heat-resistant glaze insulating layer or insulating paint.
Winding resistors have a low temperature coefficient, high resistance precision, 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 resistors
It is made by evaporating a certain resistivity material on the surface of insulating material. Mainly as follows:
4.1 Carbon film resistors
It is made by depositing crystalline carbon on the ceramic rod skeleton. Carbon film resistors have low cost, stable performance, wide resistance range, low temperature coefficient and low voltage coefficient, and are currently the most widely used resistors.
4.2 Metal film resistors.
The alloy material is evaporated on the surface of the ceramic rod skeleton by vacuum evaporation.
Metal film resistors have higher accuracy, better stability, lower noise and lower temperature coefficient than carbon film resistors. It is widely used in instrumentation and communication equipment.
4.3 Metal oxide film resistors
Deposit a layer of metal oxide on the insulating rod. Since it is an oxide itself, it is stable at high temperatures, has thermal shock resistance, and has a strong load capacity.
4.4 Synthetic membrane resistance
It is obtained by coating the conductive composite suspension on the substrate, so it is also called paint film resistance.
Because its conductive layer presents a granular structure, its noise is large and its accuracy is low. It is mainly used to manufacture high voltage, high resistance, and small resistors.
5. Metal glass uranium resistor
The metal powder and the glass uranium powder are mixed and printed on the substrate by a screen printing method.
Moisture resistance, high temperature, small temperature coefficient, mainly used in thick film circuits.
6. Chip resistance SMT
The chip resistor is a form of metal glass uranium resistance. His resistor body is made of high-conductivity ruthenium series glass uranium material after high temperature sintering. The electrode uses silver-palladium alloy slurry. Small size, high precision and good stability, because it is a chip component, so the high frequency performance is good.
7. Sensitive resistance
Sensitive resistance refers to resistors whose device characteristics are sensitive to the effects of 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 the type of the sensitive resistor is marked beside it, such as: t.v.
7.1 Varistors
There are mainly silicon carbide and zinc oxide varistor, zinc oxide has more excellent characteristics.
7.2 Humidity resistance
It consists of a moisture-sensitive layer, electrodes, and insulators. The humidity-sensitive resistors mainly include lithium chloride humidity-sensitive resistors, carbon humidity-sensitive resistors, and oxide humidity-sensitive resistors. The resistance of lithium chloride hygrostat decreases with the increase of humidity. The disadvantage is that the test range is small, the repeatability of the characteristics is not good, and it is greatly affected by temperature. The shortcomings of carbon humidity thermistors are low temperature sensitivity, resistance is greatly affected by temperature, and it is rarely used due to aging characteristics.
The oxide humidity sensor has superior performance, can be used for a long time, the temperature has little effect, and the resistance value and the humidity change have a linear relationship. There are tin oxide, nickel ferrite, and other materials.
7.3, Photoresistor
Photoresistor is an electronic component whose conductivity changes with the change of light quantity and force. When a certain substance is exposed to light, the concentration of carriers increases to increase the conductivity. This is the photoconductivity effect.
7.4. Gas-sensitive resistor
It is made of some semiconductors after absorbing a certain gas and undergoing a redox reaction. The main component is a metal oxide. The main varieties are: metal oxide gas sensitive resistor, composite oxide gas sensitive resistor, ceramic gas sensitive resistor, etc.
7.5. Force-sensitive resistor
Force-sensitive resistor is a kind of resistance whose resistance value changes with the change of pressure, and it is called piezoresistor abroad. The so-called pressure resistance effect is the effect that the resistivity of the semiconductor material changes with the change of mechanical stress. 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)-capacitance
Capacitor is one of the electronic components used in a large number of electronic equipment, widely used in DC blocking, coupling, bypass, filtering, tuning loop, energy conversion, control circuit and so on. C is used to represent capacitance. The unit of capacitance is farad (F), micro-farad (uF), picofarad (pF), 1F = 10 ^ 6uF = 10 ^ 12pF
First, the method of naming capacitors
The model of domestic capacitors generally consists of four parts (not applicable to pressure sensitive, variable, vacuum capacitors). In turn represent the name, material, classification and serial number.
The first part: the name, which is represented by letters, and the capacitor is C.
Part II: Materials, expressed in letters.
The third part: classification, generally expressed by numbers, and individually expressed by letters.
The fourth part: serial number, expressed by numbers.
Use letters to indicate product materials: A-tantal electrolysis, B-polystyrene and other non-polar films, C-high frequency ceramics, D-aluminum electrolysis, E-other materials electrolysis, G-alloy electrolysis, H-composite media, I-glass glaze, J-metallized paper, L-polyester and other polar organic films, N-niobium electrolysis, O-glass film, Q-paint film, T-low frequency ceramics, V-mica paper, Y-mica, Z -Paper Introduction

Second, the classification of capacitors
According to the structure, it is divided into three categories: fixed capacitors, variable capacitors and trimmer capacitors.
According to the electrolyte classification: organic dielectric capacitors, inorganic dielectric capacitors, electrolytic capacitors and air dielectric capacitors.
According to usage: high frequency bypass, low frequency bypass, filtering, tuning, high frequency coupling, low frequency coupling, small capacitors.
High frequency bypass: ceramic capacitor, mica capacitor, glass film capacitor, polyester capacitor, glass glaze capacitor.
Low frequency bypass: paper dielectric capacitors, ceramic capacitors, aluminum electrolytic capacitors, polyester capacitors.
Filtering: aluminum electrolytic capacitors, paper dielectric capacitors, composite paper dielectric capacitors, liquid tantalum capacitors.
Tuning: ceramic capacitors, mica capacitors, glass film capacitors, polystyrene capacitors.
3. Commonly used capacitors
1. Aluminum electrolytic capacitors
It is made of water-absorbent paper impregnated with paste electrolyte and sandwiched between two aluminum foils. A thin oxide film is used as a dielectric capacitor. Because the oxide film has unidirectional conductivity, the electrolytic capacitor has polarity. The capacity is large and can be Withstand large pulsating current, large capacity error, large leakage current; ordinary is not suitable for high frequency and low temperature applications, should not use low frequency bypass above 25kHz, signal coupling, power filter
2. Tantalum electrolytic capacitors
The sintered tantalum block is used as the positive electrode. The electrolyte uses solid manganese dioxide. 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 Small, the maximum capacitance voltage product can be obtained per unit volume. The tolerance to pulsating current is poor. If it is damaged, it is easy to be short-circuited. Ultra-small high-capacity machine
3. Film capacitors
The structure is similar to that of paper capacitors, but low-loss plastic materials such as polyester and polystyrene are used as dielectrics with good frequency characteristics. The dielectric loss is small and cannot be made into large capacity. The heat resistance is poor. Filter, integration, oscillation, timing circuit
4. Porcelain dielectric capacitor
Through-hole or pillar structure ceramic dielectric capacitor, one of its electrodes is the mounting screw. The lead inductance is very small, the frequency characteristics are good, the dielectric loss is small, and the temperature compensation function cannot be used to make a large capacity. The capacity change caused by vibration is especially suitable for high frequency bypass
5. Monolithic capacitor
(Multilayer Ceramic Capacitor) A number of ceramic film blanks are covered with electrode paddle material, and after being laminated, they are wound into an inseparable whole at a time. New high temperature resistant capacitors, high dielectric constant low frequency monolithic capacitors also have stable performance, the body is actively small, the Q value is high and the capacity error is large. Noise bypass, filter, integration, oscillation circuit
6. Paper capacitors
Generally, two aluminum foils are used as electrodes, and a capacitor paper with a thickness of 0.008 to 0.012 mm is wound and wound in the middle. The manufacturing process is simple, the price is cheap, and a large capacity can be obtained
Generally in low-frequency circuits, it cannot be used at frequencies above 3 to 4 MHz. Oil-immersed capacitors have higher withstand voltage than ordinary paper capacitors, and have better stability, suitable for high-voltage circuits
7. Trimmer capacitors
The capacitance can be adjusted within a small range and can be fixed to a certain capacitance value after adjustment.
Porcelain dielectric trimmer capacitors have a high Q value and a small volume. They can usually be divided into two types: tube type and wafer type.
8. The mica and polystyrene media are usually spring-type east, the structure is simple, but the stability is poor.
The wire-wound ceramic dielectric fine-tuning capacitor is to remove the copper wire <external electrode> to change the capacity, so the capacity can only be reduced, and it is not suitable for use in occasions where repeated debugging is required
9. Ceramic capacitors
Capacitor ceramic (barium titanate-titania) with high dielectric constant is extruded into a circular tube, disc or disc as a medium, and silver is plated on the ceramic as an electrode by infiltration method. It is divided into two kinds of high-frequency porcelain medium and low-frequency porcelain medium.
Capacitors with a small positive capacitance temperature coefficient are used in high-stability oscillation circuits as loop capacitors and matting capacitors. Low-frequency ceramic dielectric capacitors are limited to the use of bypass or DC blocking in circuits with lower operating frequencies, or occasions that do not require high stability and loss (including high frequencies). Such capacitors are not suitable for use in pulse circuits because they are easily broken down by pulse voltage. High frequency ceramic capacitors are suitable for high frequency circuits
In terms of structure, mica capacitors can be divided into foil type and silver type. The silver electrode is formed by plating a silver layer directly on the mica sheet by vacuum evaporation or infiltration. Due to the elimination of the air gap, 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 a large capacity, widely used in high-frequency appliances, and can be used as a standard capacitor
10. The glass glaze capacitor is formed by spraying a special mixture with a concentration suitable for spraying into a thin film, and the medium is then sintered with a silver layer electrode. The "monolithic" structure performance is comparable to mica capacitors and can withstand various climate environments. , Generally can work under 200 ℃ or higher temperature, rated working voltage can reach 500V, loss tgδ0.0005 ～ 0.008

4. The main characteristics of the capacitor:
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 the error, and the accuracy within the allowable deviation range.
Correspondence between accuracy level and 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 grade Ⅰ, Ⅱ, and Ⅲ, and electrolytic capacitors are grade Ⅳ, Ⅴ, and Ⅵ, depending on the application.
2. Rated voltage
It can be continuously added to the effective value of the highest DC voltage of the capacitor at the lowest ambient temperature and rated ambient temperature. It is generally directly marked on the capacitor shell. If the working voltage exceeds the withstand voltage of the capacitor, the capacitor breaks down, causing irreparable permanent damage.
3. Insulation resistance
The DC voltage is added to the capacitor and generates a leakage current. The ratio between the two is called the insulation resistance.
When the capacitance is small, it mainly depends on the surface state of the capacitor. When the capacity is greater than 0.1uf, it mainly depends on the performance of the medium. 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, which is equal to the product of the capacitor's insulation resistance and capacity.
4. Loss
Under the action of electric field, the energy consumed by heat in a unit time is called loss. All kinds of capacitors stipulate the allowable value of the loss in a certain frequency range. The loss of the capacitor is mainly caused by the dielectric loss, the conductivity loss, and the resistance of all metal parts of the capacitor.
Under the action of the DC electric field, the loss of the capacitor exists in the form of leakage conduction loss, which is generally small. Under the action of the alternating electric field, the loss of the capacitor is not only related to the leakage conduction, but also to the periodic polarization establishment process.

5. Frequency characteristics
As the frequency increases, the capacitance of general capacitors shows a law of decline.

V. Capacitor capacity labeling
1. Straight mark method
Mark it directly with numbers and unit symbols. For example, 01uF means 0.01 microfarad, some capacitors use "R" to indicate the decimal point, such as R56 means 0.56 microfarad.
2. Text symbol method
Use regular combinations of numbers and text symbols to represent capacity. For example, p10 means 0.1pF, 1p0 means 1pF, 6P8 means 6.8pF, 2u2 means
2.2uF.
3. Color standard method
The main parameters of the capacitor are represented by color circles or color points. The color coding method of the capacitor is the same as the resistance.
Capacitor deviation signs: + 100% -0--H, + 100% -10%-R, + 50% -10%-T, + 30% -10%-Q, + 50% -20% --S, + 80% -20%-Z.
Basic knowledge of circuit design (3)-inductance coil
The inductance coil is wound around the insulating tube by a circle * turn, and the wires are insulated from each other, and the insulating tube may be hollow, or may contain an iron core or a magnetic powder core, referred to as an inductor. Expressed by L, the units are Henry (H), Milli-Henry (mH), Micro-Henry (uH), 1H = 10 ^ 3mH = 10 ^ 6uH.
1. Classification of inductance
Classified by inductance form: fixed inductance and variable inductance.
Classified according to the nature of the magnet: hollow core coil, ferrite coil, iron core coil, copper core coil.
Classified according to the nature of work: antenna coil, oscillation coil, choke coil, notch coil, deflection coil.
According to the winding structure classification: single-layer coil, multi-layer coil, honeycomb coil.
2. The main characteristic parameters of the inductor coil
1. Inductance L
The inductance L represents the inherent characteristics of the coil itself, and has nothing to do with the current. In addition to the special inductance coil (color coded inductance), the inductance is generally not specifically marked on the coil, but marked with a specific name.
2. Inductive XL
The size of the inductance coil blocking the AC current is called inductive reactance XL and the unit is ohm. Its relationship with inductance L and AC frequency f is XL = 2πfL
3. Quality factor Q
Quality factor Q is a physical quantity that represents the quality of the coil, Q is the ratio of inductive reactance XL and its equivalent resistance, namely: 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 the DC resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shield or 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 existing between the turns of the coil, between the coil and the shield, and between the coil and the backplane is called distributed capacitance. The existence of distributed capacitance reduces the Q value of the coil and the stability becomes worse, so the smaller the distributed capacitance of the coil, the better.
3. Commonly used coils
1. Single layer coil
The single-layer coil is wound around the paper tube or bakelite frame with insulated wires one by one. Such as transistor radio medium wave antenna coil.
2. Honeycomb coil
If the coil is wound, its plane is not parallel to the plane of rotation, but intersects at a certain angle. Such a coil is called a honeycomb coil. The number of times the wire bends back and forth in one rotation is often called the number of vertices. The advantages of the honeycomb winding method are small volume, small distributed capacitance, and large inductance. The honeycomb coils are all wound with honeycomb winding machine. The more fold points, the smaller the distributed capacitance
3. Ferrite core and iron powder core coil
The inductance of the coil is related to the presence or absence of the magnetic core. Inserting a ferrite core into the 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 ultrashort 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 code inductor
Color-coded inductors are inductors with a fixed inductance, and the inductance marking method is marked with a color circle like resistance.
6. Choke coil (choke coil)
The coil that restricts the passage of alternating current is called a choke, divided into a high-frequency choke and a low-frequency choke.
7. Deflection coil
The deflection coil is the load of the output stage of the scanning circuit of the TV. The deflection coil requires: high deflection sensitivity, uniform magnetic field, high Q value, small size and low price.
Transformer
A transformer is a device that transforms AC voltage, current, and impedance. When AC current flows in 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. The winding connected to the power source is called the primary coil, and the remaining windings are called secondary coils.
1. Classification
Classified by cooling method: dry (self-cooling) transformer, oil-immersed (self-cooling) transformer, fluoride (evaporative cooling) transformer.
Classified according to moisture-proof methods: open transformer, potting transformer, sealed transformer.
According to the structure of iron core or coil structure: core transformer (insert core, C type core, ferrite core), shell transformer (insert core, C type core, ferrite core) Toroidal transformer, metal foil transformer.
Classified according to the number of power phases: single-phase transformer, three-phase transformer, multi-phase transformer.
Classified by application: power transformer, voltage regulating transformer, audio transformer, intermediate frequency transformer, high frequency transformer, pulse transformer.
2. Characteristic parameters of power transformer
1. Working frequency
Transformer core loss has a great relationship with frequency, so it should be designed and used according to the frequency of use. This frequency is called the operating 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 on the coil of the transformer, and it must not be greater than the specified value during operation.
4. Voltage ratio
Refers to the ratio of transformer primary voltage and secondary voltage, there is a difference between no-load voltage ratio and load voltage ratio.
5. No-load current
When the secondary of the transformer is open, the primary still has a certain current. This part of the current is called the no-load current. No-load current is composed of magnetizing current (generating magnetic flux) and iron loss current (caused by 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 at the primary when the transformer secondary is open. The main loss is the core loss, followed by the no-load current loss (copper loss) on the primary coil copper resistance, this part of the loss is very small.
7. Efficiency
Refers to the percentage of the ratio of secondary power P2 to primary power P1. Generally, the greater the rated power of the transformer, the higher the efficiency.
8. Insulation resistance
It indicates the insulation performance between each coil of the transformer and between each coil and the iron core. The level of insulation resistance is related to the performance of the insulating material used, the temperature level and the degree of humidity.
3. Characteristic parameters of audio transformer and high frequency transformer
1 Frequency response
Refers to the characteristics of transformer secondary output voltage varying with operating frequency.
2 pass band
If the output voltage of the transformer at the intermediate frequency is U0, the frequency range when the output voltage (the input voltage remains unchanged) drops to 0.707U0 is called the passband B of the transformer.
3 Primary and secondary impedance ratio
The primary and secondary transformers are connected with 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 and secondary impedance ratios. In the case of impedance matching, the transformer works in the best state and the transmission efficiency is the highest.