Main characteristic parameters of capacitor
1, nominal capacitance and allowable deviation 2, rated voltage 3, insulation resistance 4, loss 5, potential danger and safety of frequency characteristic capacitance
The potential danger of dangerous high-voltage capacitors is enlarged and edited. This paragraph is an introduction.
Definition capacitance (or capacitance) is a physical quantity, which indicates the capacity of a capacitor to hold charge. We will increase the potential difference between the two plates of the capacitor by 1 volt, which is called the capacitance of the capacitor. Physically speaking, a capacitor is an electrostatic charge storage medium (just like a bucket, you can charge it). In the absence of discharge circuit [1], the self-discharge effect/electrolytic capacitance is obvious, and the charge may exist forever, which is its characteristic). It has a wide range of uses and is an indispensable electronic component in the fields of electronics and electric power. Mainly used in power supply filtering, signal filtering, signal coupling, resonance, DC isolation and other circuits. The symbol of capacitor is C.C. = ε s/d = ε s/4 π KD (vacuum) = Q/U. In the international system of units, the unit of capacitor is Farah, abbreviated as France, and the symbol is F. The commonly used capacitor units are Millimeter Method (mF), Micrometer Method (μF), Nanometer Method (nF) and Pi Method (pF). The conversion relationship is: 1 farad (F)= 1000 millifarad (MF) = 100000 microfarads (μF) 1 microfarads (μF)= 1000 nanofarads (nf) =
Correlation formula
For a capacitor, if the potential difference between two stages is 1V when charging with 1V, the capacitance of this capacitor is 1Method, that is, C=Q/U, but the capacitance is not determined by q (charge amount) or u (voltage), that is, C=εS/4πkd. Where ε is a constant, S is the relative area of the capacitor plates, D is the distance of the capacitor plates, and K is the electrostatic force constant. The capacitance of a common parallel plate capacitor is C=εS/d, (ε is the dielectric constant of the medium between plates, S is the plate area, and D is the distance between plates. ) Define the formula C=Q/U Capacitor's electric potential energy calculation formula: E = Cu 2/2 = Qu/2 Multi-capacitor parallel calculation formula: C=C 1+C2+C3+…+Cn Multi-capacitor series calculation formula:1/C =1C65438.
Capacitance and electrostatic field
Capacitance refers to the ability to accommodate an electric field. Any electrostatic field consists of many capacitors. Where there is electrostatic field, there is capacitance, which is described by electrostatic field. It is generally believed that an isolated conductor and infinity form a capacitor, and grounding the conductor is equivalent to connecting it to infinity and connecting it to the whole earth. Various capacitors are needed in electronic manufacturing, which play different roles in the circuit. Similar to a resistor, it is usually referred to as a capacitor for short, and is represented by the letter C. As the name implies, a capacitor is a "container for storing charge". Although there are many kinds of capacitors, their basic structures and principles are the same. A capacitor consists of two closely spaced metal sheets separated by a substance (solid, gas or liquid). Two pieces of metal are called boards, and the substance in the middle is called medium. Capacitors are also divided into fixed capacity and variable capacity. But the common ones are constant capacity capacitors, and the most common ones are electrolytic capacitors and ceramic capacitors. Different capacitors have different abilities to store charge. It is stipulated that the amount of charge stored when a DC voltage of 1 volt is applied to the capacitor is called the capacitance of the capacitor. The basic unit of capacitance is farad (f). But in fact, the farad is a very unusual unit, because the capacity of the capacitor is often much smaller than 1 farad, and the commonly used methods are micro-method (μF), nano-method (nF) and micro-method (pF). The relationship between them is: 1 Farah (f) = 100000 microfarads (μF) 1 microfarads (μ f) =10000 nanofarads (NF) = 100000 picofarads (pF). Capacitors with small capacity are usually used in high-frequency circuits, such as radios, transmitters and oscillators. Large-capacity capacitors are usually used to filter and store charges. Moreover, there is another feature. Generally, capacitors above 1μF are electrolytic capacitors, and capacitors below 1μF are mostly ceramic capacitors. Of course, there are others, such as monolithic capacitors, polyester capacitors and small-capacity mica capacitors. The electrolytic capacitor has an aluminum shell, which is filled with electrolyte, and two electrodes are led out as a positive electrode (+) and a negative electrode (-). Unlike other capacitors, their polarity in the circuit cannot be wrong, while other capacitors have no polarity. Connect the two electrodes of the capacitor to the positive electrode and the negative electrode of the power supply respectively. After a period of time, even if the power supply is turned off, there will still be residual voltage between the two pins (you can observe it with a multimeter after learning the tutorial). We say that a capacitor stores charge. When a voltage is generated between the plates of a capacitor, electric energy is accumulated. This process is called capacitor charging. There is a certain voltage across the charged capacitor. The process that the charge stored in the capacitor is released into the circuit is called the discharge of the capacitor. For example, in real life, we can see that after unplugging the plug, the LED on the commercial rectifier power supply will continue to light for a while, and then gradually go out, because the capacitor inside stores the electric energy in advance and then releases it. Of course, this capacitor was originally used for filtering. As for capacitive filtering, I don't know if you have heard of the Walkman with rectifier power supply. Generally, low-quality power supply buzzes in headphones because manufacturers use small-capacity filter capacitors in order to save costs. At this time, a large-capacity electrolytic capacitor (1000μF, note that the positive electrode is connected to the positive electrode) can be connected in parallel at both ends of the power supply, which can generally improve the effect. Enthusiasts always use a capacitor of at least 1000 microfarads for filtering when making HiFi audio. The larger the filter capacitor, the closer the output voltage waveform is to DC, and the energy storage effect of the large capacitor makes the patch capacitor explode.
When a big signal comes, the circuit has enough energy to convert it into a powerful audio output. At this time, the function of large capacitor is a bit like a reservoir, which makes the original turbulent water flow output smoothly, and can also ensure the supply when a large amount of water is used downstream. In an electronic circuit, current can only flow when the capacitor is charged. After the charging process, the capacitor can't pass DC, which plays a role of "blocking DC" in the circuit. In circuits, capacitors are usually used for coupling, bypassing, filtering, etc. All of them use its characteristics of "communicating and isolating DC". So why can alternating current pass through a capacitor? Let's first look at the characteristics of alternating current. Alternating current not only changes alternately in direction, but also changes regularly in size. Connect the capacitor to the AC power supply, and charge and discharge the capacitor continuously, so that the charging current and discharging current in accordance with the alternating current change law (different phases) will flow in the circuit. The choice of capacitor involves many problems. The first is the problem of compression resistance. When the voltage across the capacitor exceeds its rated voltage, the capacitor will be broken down and damaged. Generally, the breakdown voltages of electrolytic capacitors are 6.3V, 10V, 16V, 25V, 50V, etc. [2]
Edit the model naming method of capacitor in this section.
The model of domestic capacitors generally consists of four parts (not suitable for pressure sensitive, variable and vacuum capacitors). In turn, it represents name, material, classification and serial number respectively.
The first part:
Name, in letters, capacitor with C.
The second part:
Materials, expressed in letters.
The third part:
Classification, generally expressed by numbers, individual by letters.
The fourth part:
Serial number, expressed in numbers. The materials of the products are indicated by letters: nonpolar films such as A- tantalum electrolysis, B- polystyrene, C- high frequency ceramics, D- aluminum electrolysis, E- other materials electrolysis, G- alloy electrolysis, H- composite medium, I- glass glaze, J- metallized paper, polar organic films such as L- polyester, N- niobium electrolysis, O- glass film, Q-.
Edit the capacitance classification of this paragraph.
First of all, according to the function
1. name: polyester (polyester) capacitor symbol: (CL) capacitor: 40p-4 μ Rated voltage: 63-630V Main features: small size, large capacity, resistance to damp heat and poor stability Application: low-frequency circuit with low requirements on stability and loss 2. Name: Symbol of polystyrene capacitor: (CB) Capacitance: 10p- 1μ Rated voltage: 100 V-30kV Main features: stable, low loss, large volume application: circuit with high requirements for stability and loss 3. Name: symbol of polypropylene capacitor: (CBB) Capacitance: 1000 p- 10 μ Rated voltage: 63-2000 V Main features: performance is similar to that of polystyrene, but its volume is small and its stability is slightly poor. Application: Replacing most polystyrene or mica capacitors. Name: Mica capacitor symbol: (CY) Capacitance: 10P-0. 1μ Rated voltage:100V-7kV Main features: high stability, high reliability, low temperature coefficient Application: high-frequency oscillation, pulse and other demanding circuits 5. Name: symbol of high-frequency ceramic capacitor: (CC) capacitance: 1-6800 p Rated voltage: 63-500 V Main features: low high-frequency loss and good stability Application: high-frequency circuit 6. Name: symbol of low-frequency ceramic capacitor: (CT) capacitance: 10P-4.7μ Rated voltage: 50V 50V-100V Main features: small size, low price, large loss and poor stability Application: low-frequency circuit with low requirements 7. Name: glass glaze capacitance symbol: (ci) capacitance:/kloc. 8. Name: aluminum electrolytic capacitor symbol: (CD) Capacitance: 0.47- 10000μ Rated voltage: 6.3-450V Main features: small size, large capacity, large loss and leakage. Application: power filter, low frequency coupling. Bypass, etc. 9. Name: symbol of tantalum electrolytic capacitor: (CA) Capacitance: 0.1-kloc-0/000μ Rated voltage: 6.3 6.3-125V Main features: loss and leakage are less than those of aluminum electrolytic capacitors. Usage: It can replace aluminum electrolytic capacitors 10 in demanding circuits. Name: air medium. It can be made into linear type, linear wavelength type, linear frequency type and logarithmic type according to needs. Applications: electronic instruments, radio and television equipment, etc. 1 1. Name: thin film dielectric variable capacitor symbol: variable capacitance: 15-550p. Main features: small size and light weight; A large number of applications of air medium with loss ratio: communication, broadcast receiver, etc. 12. Name: thin film dielectric trimming capacitor Symbol: variable capacitance: 1-29P Main features: large loss and small size Application: circuit compensation for tape recorders and electronic instruments 13. Name: ceramic dielectric trimming capacitor symbol: variable capacitance: 0.3-22p. Main features: small loss and small volume. Purpose: Precisely tuned high frequency oscillation circuit 14. Name: single-chip capacitor capacity range: 0.5 pf- 1 μ f withstand voltage: twice the rated voltage. Usage: widely used in electronic precision instruments. Resonance, coupling, filtering and bypass of various small electronic devices. Monolithic capacitors are characterized by large capacitance, small volume, high reliability, stable capacitance, good high temperature and humidity resistance, etc. The biggest disadvantage is that the temperature coefficient is very high, so it is unbearable to make the oscillator drift steadily. The capacitor of a 555 oscillator we made is next to 7805. After starting, the frequency of oscilloscope changes slowly, so it is much better to switch to polyester capacitor later. As far as temperature drift is concerned, the whole ceramic has a positive temperature of about+130, while CBB has a negative temperature coefficient of -230. When used in parallel in an appropriate proportion, the temperature drift can be reduced to a very small level. In terms of price, Tantalum-niobium capacitors are the most expensive, monolith and CBB are cheaper, and ceramics are the lowest, but some high-frequency zero-temperature drift black-spot ceramics are slightly more expensive, and mica capacitors have higher Q value and are slightly more expensive. It is said that monolithic capacitors are also called multilayer ceramic capacitors, which are divided into two types. 1 model has good performance, but its capacity is small, generally less than 0. 2U, and the other is called Type II, which has large capacity but average performance.
Second, according to the installation method
Insertion capacitor, patch capacitor, patch capacitor
Insertion capacitance
Thirdly, according to the function of capacitance in the circuit
The basic function of capacitor is charging and discharging, but many circuit phenomena extended from this basic charging and discharging function make capacitor have various uses, for example, in motor, we use it to produce phase shift; In photographic flash, it is used to generate high-energy instantaneous discharge and so on; In electronic circuits, capacitors have many different uses. Although there are some differences, their functions are all from charging and discharging. Here are some functions of capacitors: coupling capacitors: The capacitors used in coupling circuits are called coupling capacitors, which are widely used in capacitive coupling circuits such as resistance-capacitance coupling amplifiers to block DC- AC current. ? Filter capacitor: the capacitor used in the filter circuit is called filter capacitor, which is used in power supply filtering and various filter circuits. The filter capacitor removes the signal in a certain frequency band from the total signal. ? Decoupling capacitor, the capacitor used in decoupling circuit is called decoupling capacitor, which is used in DC power supply circuit of multistage amplifier to eliminate harmful low-frequency cross-connection between amplifiers at all levels. ? High-frequency vibration elimination capacitor: The capacitor used in high-frequency vibration elimination circuit is called high-frequency vibration elimination capacitor. In the audio negative feedback amplifier, this capacitor circuit is used to eliminate the possible high-frequency self-excited vibration, thus eliminating the possible high-frequency howling of the amplifier. ? Resonant capacitance: the capacitance used in LC resonant circuit is called resonant capacitance, which is needed in both LC parallel and series resonant circuits. ? Bypass capacitance: The capacitance used in Fibre Channel is called bypass capacitance. If you need to remove the signal of a certain frequency band from the signal, you can use. According to the frequency of the removed signal, there are full frequency domain (full AC signal) bypass capacitor circuit and high frequency bypass capacitor circuit. ? Neutralization capacitor: The capacitor used in neutralization circuit is called neutralization capacitor. This neutralizing capacitor circuit is used in radio high-frequency and intermediate-frequency amplifiers and TV high-frequency amplifiers to eliminate self-excitation. ? Timing capacitance: The capacitance used in the timing circuit is called timing capacitance. Timing capacitor circuit is used in the circuit that needs time control through capacitor charging and discharging, and the capacitor plays the role of controlling the size of time constant. ? Integrating capacitance: The capacitance used in the integrating circuit is called integrating capacitance. In the synchronous separation stage circuit of TV field scanning, this integrated capacitor circuit is used to extract the field synchronization signal from the line field composite synchronization signal. ? Differential capacitance: The capacitance used in differential circuits is called differential capacitance. In order to get the spike trigger signal in the trigger circuit, this differential capacitor circuit is used to get the spike trigger signal from various (mainly rectangular pulse) signals. ? Compensation capacitor: The capacitor used in the compensation circuit is called compensation capacitor. In the bass compensation circuit of the card holder, this low-frequency compensation capacitor circuit is used to improve the low-frequency signal in the playback signal. In addition, there is a high-frequency compensation capacitor circuit. ? Bootstrap capacitance: the capacitance used in the bootstrap circuit is called bootstrap capacitance, which is often used in the output stage circuit of OTL power amplifier to slightly increase the positive half-cycle amplitude of the signal through positive feedback. ? Frequency-dividing capacitance: The capacitance in the frequency-dividing circuit is called frequency-dividing capacitance. In the speaker frequency division circuit of the sound box, the frequency division capacitor circuit is used to make the high frequency speaker work in the high frequency band, the intermediate frequency speaker work in the middle frequency band and the low frequency speaker work in the low frequency band. ? Load capacitance: refers to the effective external capacitance that determines the resonant frequency of the load together with the quartz crystal resonator. Common standard values of load capacitance are 16pF, 20pF, 30pF, 50pF, 100pF. The load capacitance can be properly adjusted according to the specific situation, and the working frequency of the resonator can generally be adjusted to the nominal value by adjustment.
Edit the application of capacitance in this paragraph.
In many electronic products, capacitor is an essential electronic component, which plays the role of smoothing filter of rectifier, power supply and decoupling, bypass of AC signal, AC coupling of AC /DC circuit and so on. Because there are many types and structures of capacitors, users need to know not only the performance indexes and general characteristics of various capacitors, but also the advantages and disadvantages, mechanical or environmental constraints of various components in a given use. The main parameters and uses of capacitors are introduced below for readers to use when choosing capacitor types. 1. Nominal capacitance (CR): the capacitance value marked on the capacitor product. The capacitance of mica and ceramic dielectric capacitors is low (about below 5000pF); The capacitance of paper, plastic and some ceramic media is in the middle (about 0.005 μ f10 μ f); Generally, the capacity of electrolytic capacitors is relatively large. This is a rough classification. 2. Category temperature range: The ambient temperature range that can work continuously as determined by the capacitor design depends on the temperature limit of its corresponding category, such as the upper category temperature, the lower category temperature and the rated temperature (the highest ambient temperature that can continuously apply rated voltage). 3. Rated voltage (UR): the effective value of the maximum DC voltage or the maximum AC voltage or the peak value of the pulse voltage that can be continuously applied to the capacitor at any temperature between the lower limit temperature and the rated temperature. When capacitors are used in high voltage situations, we must pay attention to the influence of corona. Corona is caused by the gap between dielectric layer and electrode layer, which will not only produce parasitic signals that damage equipment, but also lead to dielectric breakdown of capacitors. Corona is particularly prone to occur under AC or pulsating conditions. For all capacitors, the sum of DC voltage and AC peak voltage should not exceed the DC voltage rating in use. 4. Tangent of loss angle (tanδ): Under the sinusoidal voltage with specified frequency, the loss power of capacitor is divided by the reactive power of capacitor. What needs to be explained here is that in practical application, the capacitor is not a pure capacitor, and there is an equivalent resistance inside it. Its simplified equivalent circuit is shown in the following figure. In the figure, C is the actual capacitance of the capacitor, Rs is the series equivalent resistance of the capacitor, Rp is the insulation resistance of the medium, and Ro is the absorption equivalent resistance of the medium. For electronic equipment, the smaller the Rs, the better, that is to say, the smaller the power loss and the smaller the angle δ with the capacitor power. This relationship is expressed by the following formula: tanδ=Rs/Xc=2πf×c×Rs. Therefore, this parameter should be carefully selected in application to avoid excessive self-heating and reduce equipment failure. 5. Temperature characteristics of capacitors: usually expressed as the percentage of the capacitance at the reference temperature of 20℃ to the capacitance at the relevant temperature. 6. Capacitor is the simplest battery, which has the advantages of fast charging and large capacity.
Edit this paragraph to supplement.
1. Capacitance is generally represented by "c" plus a number in the circuit (for example, C 13 is represented by the number 13). Capacitor is an element with two metal films attached to each other and separated by insulating material. The characteristics of capacitors are mainly blocking DC and circulating AC. The size of the capacitor means the amount of electric energy that can be stored. The blocking effect of capacitance on AC signal is called capacitive reactance, which is related to the frequency and capacitance of AC signal. Capacitance XC= 1/2πf c (f stands for the frequency of AC signal, and c stands for capacitance) The commonly used capacitor types in telephones are electrolytic capacitor, ceramic capacitor, patch capacitor, monolithic capacitor, tantalum capacitor and polyester capacitor. 2. Identification method: The identification method of capacitance is basically the same as that of resistance, which is divided into three methods: direct standard method, color standard method and number standard method. The basic unit of capacitance is farad (f), and other units are millifarad (mF), microfarad (μF)/mju:/, nanofarad (nF) and picofarad (pF). Where: 1 Farah = 1000 millifarads (mF), 1 millifarads = 1000 microfarads (μF), 1 microfarads = 1000 nanofarads (nF). For example, 10 μF/ 16V, and the capacitance value of the capacitor is expressed by letters or numbers. Letter representation:1m =1000μ f1p 2 =1.2pf1n =1000pf is represented by numbers. The first two digits of the three digits are the significant digits of the nominal capacity, and the third digit represents the number of zeros after the significant digits, all in pF. For example, 102 means that the nominal capacity is 1000pF. 22 1 means that the nominal capacity is 220pF. 224 denotes a nominal capacity of 22x 10(4)pF. There is a special case of this representation, that is, when the third digit is "9", the capacity is expressed by multiplying the significant number by-10/power. For example, 229 means that the nominal capacity is 22x (10-1) pf = 2.2pf. The allowable error is1%2% 5%10%15% 20%. For example, the capacitance of a tile is 104J, which means the capacitance is 0. 1 μF, and the error is 5%. 3 service life: the service life of capacitor decreases with the increase of temperature. The main reason is that the temperature accelerates the chemical reaction and degrades the medium with time. Insulation resistance: with the increase of temperature, the electronic activity increases, and the insulation resistance will decrease due to the increase of temperature. Capacitors include fixed capacitors and variable capacitors, in which fixed capacitors can be divided into mica capacitors, ceramic capacitors, paper/plastic film capacitors, electrolytic capacitors and glass glaze capacitors according to the dielectric materials used. Variable capacitors can also be glass, air or ceramic dielectric structures. The following table lists the letter symbols of common capacitors.
Edit the capacitance classification of this paragraph.
A. electrolytic capacitor B. solid capacitor C. ceramic capacitor D. tantalum electrolytic capacitor E. mica capacitor F. glass glaze capacitor G. polystyrene capacitor H. glass film capacitor I. alloy electrolytic capacitor J. polyester capacitor K. polypropylene capacitor L. slurry electrolytic capacitor N. aluminum electrolytic capacitor 5. Basic characteristics of capacitors: AC, DC: high frequency, low frequency.
Edit the general selection of capacitors in this paragraph.
Low frequency has a wide range of applications, such as those with poor high frequency characteristics; However, it has great limitations in high-frequency circuits, and once it is improperly selected, it will affect the overall working state of the circuit; Generally speaking, electrolytic capacitors and ceramic capacitors are used for power supply, but at high frequency, expensive capacitors such as mica are used, so you can't use polyester capacitors and electrolytic capacitors, because they will form inductance at high frequency, which will affect the working accuracy of the circuit.