resistance
The resistance of a conductor to electric current is called resistance, represented by the symbol R, and its units are ohms, kiloohms, and megaohms, which are represented by Ω, KΩ, and MΩ, respectively.
I. Resistor model naming method:
The model number of domestically produced resistors consists of four parts (excluding sensitive resistors).
Part 1: Main Name, represented by letters, indicating the product name. For example, R represents a resistor, and W represents a potentiometer.
Part Two: Materials, represented by letters, indicating the materials used to compose the resistive element: 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.
Part Three: Classification, generally represented by numbers, with some types represented by letters, indicating the product type. 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 Four : Serial Number, represented by numbers, indicating different varieties within the same product category to distinguish product dimensions and performance specifications. For example: RT11 type ordinary carbon film resistor.
II. Classification of Resistors
1. Wirewound resistors: general-purpose wirewound resistors, precision wirewound resistors, high-power wirewound resistors, and high-frequency wirewound resistors.
2. Thin film resistors: carbon film resistors, composite carbon film resistors, metal film resistors, metal oxide film resistors, chemically deposited film resistors, glass glaze film resistors, and metal nitride film resistors.
3. Solid resistors: Inorganic synthetic solid carbon resistors and organic synthetic solid carbon resistors.
4. Sensitive resistors: varistors, thermistors, photoresistors, force-sensitive resistors, gas-sensitive resistors, humidity-sensitive resistors.
III. Main Characteristic Parameters
1. Nominal resistance: The resistance value marked on the resistor.
2. Tolerance: The percentage of the difference between the nominal resistance and the actual resistance, relative to the nominal resistance, is called the resistance deviation, which indicates the resistor's accuracy. The correspondence between tolerance and accuracy class is as follows: ± 0.5 % - 0.05, ±1% - 0.1 (or 0.00), ±2% - 0.2 (or 0.00), ±5% - Class I, ±10% - Class II, ±20% - Class III
3. Rated power: The maximum power that the resistor can dissipate during long-term operation under normal atmospheric pressure of 90-106.6 kPa and ambient temperature of -55℃ to +70℃.
The rated power series of wire-wound 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 calculated from the resistance and rated power.
5. Maximum operating voltage: The maximum permissible continuous operating voltage. The maximum operating voltage is lower when operating at low atmospheric pressure.
6. Temperature coefficient: The relative change in resistance caused by a 1°C change in temperature. The smaller the temperature coefficient, the better the stability of the resistor. A positive temperature coefficient indicates that the resistance increases with increasing temperature, while a negative temperature coefficient indicates that the resistance decreases with increasing temperature.
7. Aging coefficient: The percentage change in resistance value of a resistor under long-term rated power load. It is a parameter that indicates the lifespan of a resistor.
8. Voltage coefficient: Within a specified voltage range, the relative change in resistance for every 1 volt change in voltage.
9. Noise: An irregular voltage fluctuation generated in a resistor, including thermal noise and current noise. Thermal noise is caused by the irregular free movement of electrons inside the conductor, which causes irregular voltage changes between any two points of the conductor.
IV. Resistor Value Marking Method
1. Direct marking method: The resistance value is marked on the surface of the resistor with numbers and unit symbols. The allowable error is directly expressed as a percentage. If the deviation is not marked on the resistor, it is ±20%.
2. Symbolic Resistor Method: This method uses a regular combination of Arabic numerals and symbolic text to represent the nominal resistance value. The permissible tolerance is also indicated by symbolic text. The number before the symbol represents the integer resistance value, and the numbers following it represent the first and second decimal places of the resistance value, respectively.
Letter symbols indicating allowable error
Text symbol DFGJKM
Permissible deviation: ± 0.5 % ±1% ±2% ±5% ±10% ±20%
3. Digital method: This method uses a three-digit code to indicate the nominal value of a resistor. From left to right, the first two digits represent the significant figures, and the third digit represents the exponent, i.e., the number of zeros, measured in ohms. Deviation is usually indicated using letter symbols.
4. Color coding method: Different colored stripes or dots are used to mark the nominal resistance value and permissible deviation on the surface of the resistor. Most foreign resistors use the color coding 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 is a four-ring resistor, the last ring must be gold or silver. The first two digits are significant figures, the third digit is the exponent, and the fourth digit is the tolerance.
When the resistor has five bands, the last band is spaced further apart from the previous four. The first three digits are significant figures, the fourth digit is the exponent, and the fifth digit is the tolerance.
V. Commonly Used Resistors
1. Potentiometer
A potentiometer is an electromechanical component that obtains an output voltage that is related to the displacement of the brush by the sliding of the brush on the resistive body.
1.1 Synthetic carbon film potentiometer
The resistive element is made by coating a substrate surface with ground carbon black, graphite, quartz, or other materials. This process is simple and is currently the most widely used type of potentiometer. Its advantages include high resolution, good wear resistance, and long lifespan. Disadvantages include current noise, high nonlinearity, poor moisture resistance, and poor resistance stability.
1.2 Organic Solid Potentiometer
Organic solid potentiometers are a new type of potentiometer. They are made by pressing organic resistive powder into grooves within an insulator using a heated molding process. Compared to carbon film potentiometers, organic solid potentiometers offer advantages such as better heat resistance, higher power output, higher reliability, and better wear resistance. However, they also have a larger temperature coefficient, higher dynamic noise, poorer moisture resistance, more complex manufacturing processes, and lower resistance accuracy. They are used in miniaturized, highly reliable, and highly wear-resistant electronic devices, as well as in AC and DC circuits, for regulating voltage and current.
1.3 Metal-glass uranium potentiometer
Metallic glass resistive paste is coated onto a ceramic substrate using screen printing according to a specific pattern, and then sintered at high temperature. Its characteristics include a wide resistance range, good heat resistance, strong overload capacity, and excellent moisture and wear resistance, making it a promising type of potentiometer. Its disadvantages include high contact resistance and current noise.
1.4 Wire-wound potentiometer
Wire-wound potentiometers are made by winding constantan or nichrome wire around an insulating frame as the resistive element. The advantages of wire-wound potentiometers are low contact resistance, high precision, and a small temperature coefficient. Their disadvantages include poor resolution, relatively low resistance, and poor high-frequency characteristics. They are mainly used as voltage dividers, rheostats, and for zeroing and setting operating points in instruments.
1.5 Metal Film Potentiometer
The resistive element of a metal film potentiometer can be composed of alloy film, metal oxide film, metal foil, etc. Its characteristics include high resolution, high temperature resistance, small temperature coefficient, low dynamic noise, and good smoothness.
1.6 Conductive Plastic Potentiometer
DAP resistive paste is coated onto an insulating substrate using a special process and then heated to polymerize into a resistive film, or DAP resistive powder is thermoplastically pressed into grooves in an insulating substrate to form a solid resistive body. Its characteristics include: good smoothness, excellent resolution, good wear resistance, long lifespan, low dynamic noise, extremely high reliability, and resistance to chemical corrosion. It is used in servo systems for space devices, missiles, and aircraft radar antennas, etc.
1.7 Potentiometer with switch
There are rotary switch potentiometers, push-pull switch potentiometers, and push-button switch potentiometers.
1.8 Preset Potentiometer
Once a preset potentiometer is properly adjusted in a circuit, its position is sealed with wax and it is generally not adjusted again.
1.9 Sliding Potentiometer
The resistance value is changed by sliding the slider.
1.10 Dual Potentiometer
There are off-axis dual potentiometers and coaxial dual potentiometers.
1.11 Contactless Potentiometer
Contactless potentiometers eliminate mechanical contact, have a long lifespan and high reliability, and are classified into photoelectric potentiometers and magnetic potentiometers, etc.
2. Solid carbon resistor
Resistors are made by mixing carbonaceous granules, conductive materials, fillers, and binders into a single solid component. They are inexpensive, but suffer from high resistance error, high noise voltage, and poor stability, and are therefore rarely used today.
3. Wire-wound resistor
It is made by winding high-resistivity alloy wire onto an insulating frame, and then coating it with a heat-resistant glaze or insulating varnish. Wire-wound resistors have a low temperature coefficient, high resistance accuracy, good stability, and are heat and corrosion resistant. They are mainly used as precision high-power resistors. The disadvantages are poor high-frequency performance and a large time constant.
4. Thin film resistors
It is manufactured by evaporating a material with a certain resistivity onto the surface of an insulating material. The main methods are as follows:
4.1 Carbon film resistors
Carbon film resistors are fabricated by depositing crystalline carbon onto a ceramic rod substrate. They are low-cost, stable, have a wide resistance range, and low temperature and voltage coefficients, making them the most widely used type of resistor.
4.2 Metal film resistors.
Alloy materials are deposited onto the surface of a ceramic rod skeleton using vacuum evaporation. Metal film resistors offer higher accuracy, better stability, lower noise, and a smaller temperature coefficient compared to carbon film resistors. They are widely used in instruments and communication equipment.
4.3 Metal Oxide Film Resistors
A layer of metal oxide is deposited on the insulating rod. Because it is an oxide, it is stable at high temperatures, resistant to thermal shock, and has a strong load-bearing capacity.
4.4 Synthetic Film Resistivity
It is made by coating a conductive composite suspension onto a substrate, hence the name "varnish film resistor". Due to the granular structure of its conductive layer, it has high noise and low precision, and is mainly used to manufacture high-voltage, high-resistance, small resistors.
5. Metal-glass uranium resistor
Metal powder and glass uranium powder are mixed and printed onto a substrate using screen printing. It is resistant to moisture and high temperatures, has a small temperature coefficient, and is mainly used in thick-film circuits.
6. Surface Mount Resistors (SMT)
Chip resistors are a type of metallic glass-uranium resistor. Their resistive element is made of highly reliable ruthenium-based glass-uranium material sintered at high temperatures, and the electrodes use a silver-palladium alloy paste. They are small in size, highly precise, and have good stability. Due to their chip-shaped nature, they also exhibit excellent high-frequency performance.
7. Sensitive resistor
A sensitive resistor is a resistor whose characteristics are sensitive to the effects of temperature, voltage, humidity, light, gas, magnetic field, pressure, etc. The symbol for a sensitive resistor is the same as the symbol for a regular resistor with a slash added, and the type of sensitive resistor is indicated next to it, such as: t , v, etc.
7.1 Varistor
The main types are silicon carbide and zinc oxide varistors, with zinc oxide having more superior properties.
7.2 Humidity-sensitive resistor
Composed of a moisture-sensing layer, electrodes, and an insulator, humidity-sensitive resistors mainly include lithium chloride humidity-sensitive resistors, carbon humidity-sensitive resistors, and oxide humidity-sensitive resistors. Lithium chloride humidity-sensitive resistors exhibit decreasing resistance as humidity increases, but their disadvantages include a small testing range, poor repeatability, and significant temperature sensitivity. Carbon humidity-sensitive resistors suffer from low-temperature sensitivity, significant temperature-dependent resistance, and aging characteristics, leading to their less common use. Oxide humidity-sensitive resistors offer superior performance, long-term usability, minimal temperature influence, and a linear relationship between resistance and humidity changes. Materials include tin oxide and nickel iron oxide.
7.3 Photoresistor
A photoresistor is an electronic component whose conductivity changes with the amount of light. When a substance is exposed to light, the concentration of charge carriers increases, thereby increasing the conductivity. This is the photoconductive effect.
7.4 Gas-sensitive resistor
Gas-sensitive resistors are made by utilizing the oxidation-reduction reaction that occurs when certain semiconductors absorb a certain gas. Their main component is metal oxide, and the main types include: metal oxide gas-sensitive resistors, composite oxide gas-sensitive resistors, and ceramic gas-sensitive resistors.
7.5 Force-sensitive resistor
A piezoelectric resistor is a resistor whose resistance changes with pressure. The so-called piezoelectric effect refers to the change in resistivity of a semiconductor material with mechanical stress. Piezoelectric resistors can be used to make various torque meters, semiconductor microphones, pressure sensors, etc. The main types are silicon piezoelectric resistors and selenium-tellurium alloy piezoelectric resistors; relatively speaking, alloy resistors have higher sensitivity.
7.6 Thermistor
A thermistor is a type of sensitive element whose resistance changes abruptly with the temperature of the thermistor itself , exhibiting semiconductor characteristics .
Thermistors are classified into two types according to their temperature coefficient : positive temperature coefficient thermistors (PTC thermistors) and negative temperature coefficient thermistors (NTC thermistors).
Positive Temperature Coefficient Thermistor
PTC is an abbreviation for Positive Temperature Coefficient , which refers to semiconductor materials or components with a large positive temperature coefficient . Usually, when we mention PTC , we are referring to a positive temperature coefficient thermistor , or simply a PTC thermistor .
PTC thermistors are a typical type of temperature-sensitive semiconductor resistors . Above a certain temperature (Curie temperature) , their resistance increases in a stepwise manner as the temperature rises .
PTC thermistors are classified into two types based on their materials : ceramic PTC thermistors and organic polymer PTC thermistors.
Currently, the most widely used types of PTC thermistors are:
PTC thermistor for constant temperature heating
PTC thermistor for overcurrent protection
PTC thermistors for air heating
PTC thermistor for delayed start
PTC thermistor for sensor
PTC thermistor for automatic demagnetization
Generally , organic polymer PTC thermistors are suitable for overcurrent protection applications , while ceramic PTC thermistors can be used for all the applications listed above .
Negative Temperature Coefficient Thermistor (NTC Thermistor)
NTC is an abbreviation for Negative Temperature Coefficient , which generally refers to semiconductor materials or components with a large negative temperature coefficient . Usually, when we mention NTC , we are referring to negative temperature coefficient thermistors , or simply NTC thermistors .
An NTC thermistor is a typical temperature-sensitive semiconductor resistor whose resistance decreases in a stepwise manner as the temperature increases .
NTC thermistors are manufactured using ceramic processes with metal oxides such as manganese, cobalt, nickel, and copper as the main materials . These metal oxide materials all have semiconductor properties because they conduct electricity in a manner completely similar to semiconductor materials such as germanium and silicon . At low temperatures, these oxide materials have fewer charge carriers (electrons and holes), so their resistance is higher; as the temperature increases, the number of charge carriers increases, so the resistance decreases .
NTC thermistors are classified according to their applications :
Power NTC thermistor
Compensated NTC thermistor
Temperature-sensing NTC thermistor
capacitance
Capacitors are among the most widely used electronic components in electronic devices, extensively applied in DC blocking, coupling, bypassing, filtering, tuning circuits, energy conversion, and control circuits. Capacitors are represented by C, and units of capacitance include farads (F), microfarads (µF), and picofarads (pF) , where 1F = 10^6 µF = 10^12 pF.
I. Capacitor Model Naming Method
The model designation of domestically produced capacitors generally consists of four parts (not applicable to varistors, variable capacitors, and vacuum capacitors). These parts represent the name, material, classification, and serial number, respectively.
Part 1: Name, represented by letters, C for capacitors.
Part Two: Materials, represented by letters.
Part Three: Classification, generally represented by numbers, with some exceptions represented by letters.
Part Four: Serial Number, represented by numbers.
The materials used to represent the products are indicated by letters: A - Tantalum electrolysis, B - Non-polar thin films such as polystyrene, C - High-frequency ceramics, D - Aluminum electrolysis, E - Electrolysis of other materials, G - Alloy electrolysis, H - Composite dielectric, I - Glass glaze, J - Metallized paper, L - Polar organic thin films such as polyester, N - Niobium electrolysis, O - Glass film, Q - Paint film, T - Low-frequency ceramics, V - Mica paper, Y - Mica, Z - Paper media
II. Classification of Capacitors
According to their structure, they can be divided into three main categories: fixed capacitors, variable capacitors, and trimmer capacitors.
According to the electrolyte, capacitors can be classified as: organic dielectric capacitors, inorganic dielectric capacitors, electrolytic capacitors, and air dielectric capacitors.
According to their uses, they can be 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 capacitors, ceramic capacitors, aluminum electrolytic capacitors, polyester capacitors.
Filtering: Aluminum electrolytic capacitors, paper capacitors, composite paper capacitors, liquid tantalum capacitors.
Tuning: Ceramic capacitors, mica capacitors, glass film capacitors, polystyrene capacitors.
High-frequency coupling: ceramic capacitors, mica capacitors, polystyrene capacitors.
Low-frequency coupling: paper capacitors, ceramic capacitors, aluminum electrolytic capacitors, polyester capacitors, solid tantalum capacitors.
Small capacitors: metallized paper capacitors, ceramic capacitors, aluminum electrolytic capacitors, polystyrene capacitors, solid tantalum capacitors, glass enamel capacitors, metallized polyester capacitors, polypropylene capacitors, and mica capacitors.
III. Commonly Used Capacitors
1. Aluminum electrolytic capacitors
Electrolytic capacitors are made by winding absorbent paper soaked in a paste-like electrolyte between two aluminum foils, using a thin oxide film as the dielectric . Because the oxide film has unidirectional conductivity , electrolytic capacitors are polarized . They have large capacitance and can withstand large pulsating currents, but large capacitance error and leakage current. Ordinary ones are not suitable for high-frequency and low-temperature applications , and are not suitable for use above 25kHz. They are also used for low-frequency bypass, signal coupling, and power supply filtering.
2. Tantalum electrolytic capacitor
Using sintered tantalum blocks as the positive electrode and solid manganese dioxide as the electrolyte , the temperature characteristics, frequency characteristics, and reliability are superior to ordinary electrolytic capacitors. In particular, it has extremely low leakage current, good storage properties, long lifespan, small capacitance error, and small size, achieving the maximum capacitance-voltage product per unit volume. It has poor tolerance to pulsating current and is prone to short-circuiting if damaged. This is a characteristic of ultra-miniature, highly reliable components.
3. Film capacitors
The structure is similar to that of paper capacitors, but it uses low-loss plastic materials such as polyester and polystyrene as dielectrics, resulting in good frequency characteristics, low dielectric loss, and limited capacitance. It also has poor heat resistance. (This is relevant to filter, integrator, oscillator, and timing circuits.)
4. Ceramic capacitors
In a feedthrough or pillar-type ceramic capacitor, one electrode is the mounting screw. It features extremely low lead inductance, excellent frequency characteristics, low dielectric loss, and temperature compensation. While it cannot be made with large capacitances, its capacitance changes due to vibration. It is particularly suitable for high-frequency bypassing.
5. Monolithic capacitors
(Multilayer ceramic capacitors) are novel capacitors made by coating several ceramic film blanks with electrode paste material, stacking them, and then winding them into an inseparable whole. The outer layer is then encapsulated with resin to create a small-volume, high-capacity, highly reliable, and high-temperature resistant capacitor. Low-frequency monolithic capacitors with high dielectric constants also exhibit stable performance, extremely small size, high Q value, and relatively large capacitance error. They are suitable for noise bypass, filtering, integration, and oscillation circuits.
6. Paper capacitors
Typically, two aluminum foils are used as electrodes, separated and overlapped by capacitor paper with a thickness of 0.008–0.012 mm, and then wound together. The manufacturing process is simple, inexpensive, and yields a large capacitance.
Generally, oil-immersed capacitors are not suitable for use in low-frequency circuits at frequencies above 3-4 MHz. They have a higher voltage rating and better stability than ordinary paper capacitors, making them suitable for high-voltage circuits.
7. Trimming capacitor
The capacitance can be adjusted within a small range and can be fixed at a certain capacitance value after adjustment.
Ceramic trimmer capacitors have high Q values and small size, and are generally divided into two types: cylindrical tube type and disc type.
8. Mica and polystyrene media usually use spring-type springs, which have a simple structure but poor stability.
Wire-wound ceramic trimmer capacitors change capacitance by removing copper wire (external electrodes), therefore the capacitance can only decrease, making them unsuitable for applications requiring repeated adjustments.
9. Ceramic capacitors
It is made by extruding high dielectric constant capacitor ceramic (barium titanate titanium oxide) into round tubes, discs, or disks as the dielectric, and then using a sintering process to plate silver onto the ceramic as the electrode. It is further divided into high-frequency ceramic dielectrics and low-frequency ceramic dielectrics.
Capacitors with a small positive temperature coefficient of capacitance are used in highly stable oscillating circuits as loop capacitors and padding capacitors. Low-frequency ceramic capacitors are limited to bypass or DC blocking applications in circuits with lower operating frequencies, or in applications where stability and loss requirements are not high (including high frequencies). These capacitors are 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.
Structurally, mica capacitors can be divided into foil type and silver-plated type. Silver-plated capacitors are made by directly depositing a silver layer onto a mica sheet using vacuum evaporation or sintering methods. Because air gaps are eliminated, the temperature coefficient is greatly reduced, and the capacitance stability is higher than that of foil type capacitors. They have good frequency characteristics, high Q value, and a small temperature coefficient, limiting their ability to be made into large capacitances. They are widely used in high-frequency electrical appliances and can also be used as standard capacitors.
10. Glass glaze capacitors are made by spraying a special mixture of suitable concentration into a thin film, with the dielectric then sintered with silver electrodes to form a "monolith" structure. Their performance is comparable to mica capacitors, and they can withstand various climatic environments, generally operating at 200℃ or higher. The rated operating voltage can reach 500V, and the loss tgδ is 0.0005～ 0.008 .
IV. Main characteristic parameters of capacitors
1. Nominal capacitance and permissible deviation
Nominal capacitance is the capacitance marked on a capacitor.
The deviation between the actual capacitance and the nominal capacitance of a capacitor is called error; the allowable deviation range is called accuracy.
The correspondence between accuracy class and permissible error is as follows: 00 (01) - ±1%, 0 (02) - ±2%, Ⅰ - ±5%, Ⅱ - ±10%, Ⅲ - ±20%, Ⅳ - (+20% - 10%), Ⅴ - (+50% - 20%), Ⅵ - (+50% - 30%)
General capacitors are commonly classified as I, II, and III, while electrolytic capacitors are classified as IV, V, and VI, depending on the application.
2. Rated voltage
The maximum effective DC voltage that can be continuously applied to a capacitor at the lowest and rated ambient temperatures is usually marked directly on the capacitor casing. If the operating voltage exceeds the capacitor's withstand voltage, the capacitor will break down, causing irreparable permanent damage.
3. Insulation resistance
A DC voltage is applied across a capacitor, generating a leakage current. The ratio of the leakage current to the voltage is called the insulation resistance .
When the capacitance is small, it mainly depends on the surface condition of the capacitor . When the capacitance is >0.1uF, it mainly depends on the properties of the dielectric. The lower the insulation resistance, the better.
Capacitor time constant: A time constant is introduced to properly evaluate the insulation performance of large-capacity capacitors. It is equal to the product of the capacitor's insulation resistance and capacitance.
4. Losses
The energy consumed by a capacitor due to heat generation per unit time under the influence of an electric field is called loss. Various types of capacitors have specified allowable loss values within a certain frequency range. Capacitor loss is mainly caused by dielectric loss, conductivity loss, and the resistance of all metal parts of the capacitor.
Under the influence of a DC electric field, the loss of a capacitor exists in the form of leakage conduction loss, which is generally small. Under the influence 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 typical capacitor generally decreases.
V. Capacitor Capacity Marking
1. Direct labeling method
Capacitors are directly labeled with numbers and unit symbols. For example, 01uF represents 0.01 microfarads. Some capacitors use "R" to represent the decimal point, such as R56, which represents 0.56 microfarads.
2. Method of using written symbols
Capacity is represented by a regular combination of numbers and letter symbols. For example, p10 represents 0.1 pF , 1p0 represents 1 pF , 6p8 represents 6.8 pF , and 2u2 represents 2.2 uF .
3. Color mark method
The main parameters of a capacitor are indicated using color rings or dots. The color coding system for capacitors is the same as that for resistors.
Capacitor deviation marking symbols: +100%-0--H, +100%-10%--R, +50%-10%--T, +30%-10%--Q, +50%-20%--S, +80%-20%--Z.
inductance
An inductor is made by winding a conductor one turn after another around an insulating tube. The conductors are insulated from each other, and the insulating tube can be hollow or contain an iron core or a magnetic powder core. It is simply called inductance. It is represented by L, and the units are Henry (H), millihenry (mH), and microhenry (uH), where 1H = 10^3 mH = 10^6 uH.
I. Classification of Inductors
Inductors can be classified by their type: fixed inductors and variable inductors.
According to the properties of the magnetic conductor: air-core coils, ferrite coils, iron-core coils, and copper-core coils.
Classified by function: antenna coil, oscillator coil, choke coil, trap coil, deflector coil.
According to the winding structure, coils can be classified as: single-layer coils, multi-layer coils, and honeycomb coils.
II. Main characteristic parameters of inductors
1. Inductance L
Inductance L represents the inherent characteristic of the coil itself and is independent of the current magnitude. Except for dedicated inductor coils (color-coded inductors), the inductance is generally not specifically marked on the coil, but rather indicated by a specific name.
2. Anti-infective XL
The magnitude of the opposition to alternating current by an inductor is called inductive reactance XL, and its unit is ohms. It is related to the inductance L and the frequency f of the alternating current by the formula: XL = 2πfL
3. Quality Factor Q
The quality factor Q is a physical quantity that represents the quality of a coil. Q is the ratio of the inductive reactance XL to its equivalent resistance, i.e.: Q = XL/R
The higher the Q value of a coil, the lower the circuit loss. The Q value of a coil is related to factors such as the DC resistance of the conductor, the dielectric loss of the core, the loss caused by the shield or core, and the effect of the high-frequency skin effect. The Q value of a coil is typically in the range of tens to hundreds.
4. Distributed capacitance
The capacitance existing between turns of a coil, between the coil and the shield, and between the coil and the base plate is called distributed capacitance. The presence of distributed capacitance reduces the Q value of the coil and worsens its stability; therefore, the smaller the distributed capacitance of the coil, the better.
III. Commonly Used Coils
1. Single-layer coil
A single-layer coil is made by winding insulated wire one turn after another around a paper tube or bakelite frame. An example is the medium-wave antenna coil in a transistor radio.
2. Honeycomb coil
If the plane of the wound coil is not parallel to the plane of rotation, but intersects it at a certain angle, this type of coil is called a honeycomb coil. The number of times the wire bends back and forth in one revolution is often called the number of bends. The advantages of honeycomb winding are small size, low distributed capacitance, and high inductance. Honeycomb coils are all wound using a honeycomb winding machine; the more bends, the smaller the distributed capacitance.
3. Ferrite core and iron powder core coils
The inductance of a coil is related to the presence or absence of a magnetic core. Inserting a ferrite core into an air-core coil can increase the inductance and improve the coil's quality factor.
4. Copper core coil
Copper core coils are widely used in the ultra-shortwave range. The inductance is changed by rotating the position of the copper core in the coil, which is a convenient and durable adjustment method.
5. Color-coded inductors
Color-coded inductors are inductors with a fixed inductance value, and their inductance value is marked using color rings, just like resistors.
6. Choke (or baffle)
A coil that restricts the flow of alternating current is called a choke coil, which is divided into high-frequency choke coils and low-frequency choke coils.
7. Deflection coil
The deflection coil is the load of the output stage of the scanning circuit of a TV. The requirements for the deflection coil are: high deflection sensitivity, uniform magnetic field, high Q value, small size and low price.
