“When used as a battery power supply, it has the function of an AC path, which is equivalent to short-circuiting the battery’s AC signal, avoiding the increase in battery internal resistance due to the battery voltage drop, and the parasitic oscillation of the circuit.
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1. The positive and negative ends of the voltage source are connected to a capacitor (parallel to the circuit), which has a good filtering effect when used in a rectifier circuit. When the voltage is alternating, due to the charging effect of the capacitor, the voltage at both ends cannot be changed suddenly. The voltage is stable.
When used as a battery power supply, it has the function of an AC path, which is equivalent to short-circuiting the battery’s AC signal, avoiding the increase in battery internal resistance due to the battery voltage drop, and the parasitic oscillation of the circuit.
2. For example, in what kind of circuit, a series or parallel capacitor can achieve the coupling effect, and what is the difference between a non-discharged capacitor and a discharge capacitor?
In the AC multi-stage amplifier circuit, due to the different gains and powers of each stage, the DC working offset values of each stage are different! If the stages are directly coupled, the working offset values of each stage will be mixed and cannot work normally! The cross-stratification feature not only solves the coupling of inter-level communication, but also isolates the inter-level partial value mixing, killing two birds with one stone!
3. The two coupling capacitors in the basic amplifying circuit, the capacitor + pole and the DC + pole are connected, which play a role in the communication and isolation. , Why do you want to pick it up!
If the connection is reversed, the electrolytic capacitor will leak, which will change the DC operating point of the circuit and make the amplifying circuit abnormal or unable to work.
4. What is the role of the capacitor in the resistance-capacitance coupling amplifier circuit?
Isolate the DC signal so that the static operating points of adjacent amplifying circuits are independent of each other and do not affect each other.
5. Can the analog circuit amplifier not use coupling capacitors? It can still be amplified? The amplifier in the book adds a coupling capacitor between the transformer secondary coil and the transistor. The explanation is that the output of the previous stage becomes the input of the next stage. , So that the front and rear stages are not affected. The first stage is alternating current, and the latter is also alternating current. How can they affect each other? I really can’t figure out that adding a capacitor is not a superfluous act.
You made a mistake. The former stage is indeed alternating current, but the latter stage is alternating current superimposed direct current. The triode needs a DC bias. If there is no capacitor to block the DC, the coil of the transformer will bypass the DC bias of the transistor (because the Inductor is DC)
6. The basic amplifier circuit coupling capacitor, can the coupling capacitor be non-polar?
In the basic amplifying circuit, the coupling capacitor depends on the video frequency. When the frequency is high, a non-polar capacitor is needed. It is characterized by relatively stable, withstand voltage can be made relatively high, relatively small in size, but not large in capacity. Its biggest use is to cut off direct current through alternating current, and it is widely used in high-frequency alternating current paths, bypass, resonance and other circuits. (Simply understood as high frequency path)
When the frequency is low, since the capacity of the non-polar capacitor is relatively low, the capacitive reactance is relatively increased, so it is necessary to use a polar electrolytic capacitor. Because of the electrolyte inside, the capacity can be made large, allowing low-frequency alternating current to pass through , Cut off direct current. However, because of the organic medium between the internal two poles, the withstand voltage is limited, and it is mostly used in circuits such as low-frequency AC paths, filtering, decoupling, and bypassing. (Simply understood as the low-frequency path)
7. Please tell the circuit expert what is the role of the coupling capacitor
In the amplifying circuit, the use of the coupling capacitor to pass the DC blocking function allows the high-frequency AC signal to pass through the circuit smoothly and be amplified one by one, while the DC quantity is blocked inside each stage.
8. In a battery-powered circuit, why does the capacitor charge and discharge to delay the function? Thank you, master.
Capacitors accumulate electric charge, you can think of it as a water cup, charging and discharging are charging and discharging water. During the charging process, the voltage rises slowly, while discharging vice versa. You only need to detect the voltage across the capacitor to achieve the delay. Such as charging, at the beginning, the voltage across the capacitor is zero, as the charging time increases, the voltage gradually rises to the voltage you set to control the switching of the circuit. Of course, the discharge can also be used in reverse. The delay time is related to capacitor capacity, capacitor leakage, charging resistance, and voltage, and sometimes load resistance is also taken into consideration.
9. Resistance-capacitance coupling is to use the capacitor’s pass-through and DC-blocking characteristics to prevent the DC component between the front and back stages from causing crosstalk and causing instability of the operating point.
10. The resistance-capacitance coupling amplifier circuit can only amplify AC signals, not DC signals, right or wrong
right. A capacitor is an Electronic component that blocks DC and AC. Therefore, the resistance-capacitance coupling amplifier circuit can only amplify the AC signal. A direct coupling amplifier circuit is used to amplify the DC signal.
11. How to distinguish the coupling capacitor and the bypass capacitor in the amplifying circuit?
The negative pole of the coupling capacitor is not grounded, but is connected to the input terminal of the next stage, and the negative pole of the bypass capacitor is grounded.
12. How to choose capacitive coupling for the multi-stage AC amplifier circuit of the op amp?
In fact, it is very simple, ordinary ceramic capacitors can be done! For good results, tantalum capacitors can be used. According to the frequency range of your input signal, you can choose capacitors with capacitances of 103,104 for high frequencies, and electrolytic capacitors with about 22uF can be used for lower frequency AC signals.
13. The amplifying circuit adopts direct coupling, and the feedback network is a pure resistance network. Why is the circuit only possible to produce high-frequency oscillation?
The oscillation originates from the closed-loop phase shift up to 180 degrees and the loop gain at this time is greater than zero. Using a pure resistance network as a feedback network will definitely not introduce phase shift, so all the phase shift comes from the open loop circuit of the amplifier. Using a direct-coupled open-loop amplifier, there will be no capacitive elements between stages that will cause a phase shift. What can cause a phase shift is the capacitance inside the transistor or MOS tube. These capacitances are all fF, the maximum pF capacitance. The resonant frequency of the circuit composed of these capacitors and the equivalent resistance of the circuit is quite high. Therefore, the amplifier adopts direct coupling, and the feedback network is a pure resistance network, which can only produce high-frequency oscillation.
14. The bandwidth of the resistance-capacitance coupling amplifier circuit refers to (the difference between the upper limit cut-off frequency and the lower limit cut-off frequency) the upper cut-off frequency of the resistance-capacitance coupling amplifier circuit refers to (as the frequency increases, the amplification factor decreases to 0.707 times, That is, the frequency at -3dB) The lower cut-off frequency of the resistance-capacitance coupling amplifier circuit refers to (as the frequency decreases, the amplification factor drops to 0.707 times the original, that is, the frequency at -3dB).The upper cut-off frequency of the RC coupling amplifier circuit is mainly affected by (transistor junction capacitance, the distributed capacitance of the circuit), and the lower cut-off frequency of the RC coupling amplifier circuit is mainly affected by the capacitor (blocking capacitor and bypass).
15. How to choose capacitive coupling for the multi-stage AC amplifier circuit of the op amp?
In fact, it is very simple, ordinary ceramic capacitors can be done! For good results, tantalum capacitors can be used. According to the frequency range of your input signal, you can choose capacitors with capacitances of 103,104 for high frequencies, and electrolytic capacitors with about 22uF can be used for lower frequency AC signals.
16. In the multi-stage amplifier circuit, how does the electrolytic capacitor couple to the next stage? Isn’t the characteristic in the capacitor blocking the direct current? How does it pass through? And because the capacitor needs to be connected through the collector of the triode, why not the transmitter? Electrolytic capacitors work in AC amplifiers, and the direction of AC current changes periodically, can the transistor be turned on normally? Also, isn’t the collector of the NPN transistor from C to B? How does its current flow to the base of the next-stage transistor?
The amplifiers that use electrolytic capacitors as couplings are all AC amplifiers. Electrolytic capacitors are used here as “passing and blocking”. Which pole of the triode outputs is a matter of circuit form, and both have.
17. 1. How to estimate the output resistance of the first-stage amplifier and the input resistance of the second-stage amplifier, 2. When the amplitude of the signal source is too large, what will happen to the output of the two-stage amplifier. 3. Shake the input end of the amplifier with your hand and observe the output end of the amplifier to see if something appears? what is the reason?
(1) The input resistance of the second-stage amplifier is the output resistance of the first-stage amplifier.
(2) Distortion.
(3) Clutter, human body induction
18. Capacitors can play a coupling role? For example, in what kind of circuit, a series or parallel capacitor can achieve the effect of coupling, and what is the difference between a non-discharged capacitor and a discharge capacitor?
In the AC multi-stage amplifier circuit, due to the different gains and powers of each stage, the DC working offset values of each stage are different! If the stages are directly coupled, the working offset values of each stage will be mixed and cannot work normally! The cross-stratification feature not only solves the coupling of inter-level communication, but also isolates the inter-level partial value mixing, killing two birds with one stone!
19. How to use the charge and discharge of capacitors, understand filtering, decoupling, bypass… Capacitors are charging and discharging. How to use the charge and discharge of capacitors to understand filtering, decoupling, bypass…
Capacitors block DC and pass AC. DC blocking is easy to understand, but AC is not easy to understand. As long as you understand passing AC, you can understand filtering, decoupling and bypass.
Capacitors are charging and discharging, which is good. But the direction of alternating current changes alternately. The magnitude of the amplitude also changes periodically. The entire changing image is a sine curve.
The capacitor is connected to the AC circuit, and due to the periodic change of the AC voltage, it is also periodically changing in charge and discharge. There are charging and discharging currents in the circuit. This charging and discharging current has the same shape as the voltage, except that the phase is 90 degrees ahead of the voltage, which is equivalent to the AC passing through the capacitor.
It is different from alternating current passing through a resistor. Alternating current passing through a resistor consumes electrical energy (heating) on the resistor. However, the capacitor only exchanges energy with the power supply. The power supply sends energy to the capacitor when charging, and the capacitor returns the electrical energy to the power supply when discharging. Therefore, the power generated by multiplying the voltage by the current here is called reactive power.
What needs to be clear is that when the capacitor is connected to an AC circuit, the flowing electrons (current) do not really rush through the insulating layer, but generate current in the circuit. This is because in the circuit, reverse discharge and forward charge are in the same direction, and forward discharge and reverse charge are in the same direction. It is like a relay race. One team runs the positive half-week of AC power, and the other team takes over. The baton continues to run through the negative half of the alternating current. Understand that the capacitor is connected to AC, then the AC component is bypassed to the ground and the filtering is completed.
20. How to use bypass capacitors, filter capacitors, and decoupling capacitors? Some examples can be given.
Answer: The three types of capacitors are actually used for filtering, but they are used in different circuits, and their names and usages are different.
Filter capacitor, this is the capacitor we usually use after power rectification. It is a capacitor that rectifies the AC of the rectifier circuit into a pulsating DC and smoothes it through charging and discharging. This type of capacitor is generally an electrolytic capacitor with a large capacity. Law level.
Bypass capacitors are used to filter out high frequency components in the input signal. They are mainly used to filter out high frequency clutter. Usually, ceramic capacitors and polyester capacitors are used. The capacity is small and is at the picofarad level.
The decoupling capacitor takes the interference of the output signal as the filtering object. The decoupling capacitor is equivalent to the battery and uses its charge and discharge so that the amplified signal will not be interfered by the sudden change of the current. Its capacity depends on the frequency of the signal and the degree of ripple suppression.
21. What are coupling capacitors and decoupling capacitors, and what are their characteristics and functions?
The coupling capacitor is used to transmit AC signals and is connected to the circuit. The decoupling capacitor removes useless AC signals, one section is connected to the line and one end is grounded.
22. Regarding the functions of capacitors, under what circumstances is capacitive coupling and under what conditions is capacitive filtering?
Answer: The eighteen martial arts of the capacitor in the circuit are in the final analysis two! Charge charge! Discharge charge!
Its characteristic is to pass AC! Block DC! After the alternating voltage is applied to the two ends of the capacitor, it will continue to charge and discharge with the alternating frequency of the current! At this time, there is an alternating current of the same frequency in the circuit! This is the pass of the capacitor characteristic!
When the frequency is right, the capacitor can be regarded as a path to the circuit! The AC output of the previous stage can be transmitted to the subsequent circuit through the capacitor!
For DC, it is isolated! Because when the voltage at both ends is equal to the circuit voltage, there will be no more charging current!
When acting on the transmission of the front and rear AC signals, it is coupling!
When it acts to filter out fluctuation components and useless AC components, it is filtering!
23. Everyone knows that the capacitor filter of the rectifier circuit uses its charge and discharge; but sometimes the filter uses the capacitor to have a different capacitive reactance to the unpassed frequency signal, such as a bypass capacitor. So which angle is used when analyzing capacitor filtering?
In fact, no matter what kind of statement is the same, the theory of using charge and discharge is more general, and the theory of using capacitive reactance is more in-depth. The role of capacitor is to use its charge and discharge characteristics, depending on what components you want to filter out. A large capacitor is used to filter low frequencies, and a small capacitor is used to filter high frequencies. In theory, the filtering in the low-frequency rectifier circuit and the bypass in the high-frequency are the same, and the difference in capacitive reactance is used.
24. How does the capacitor realize the functions of charging and discharging, rectification, and filtering?
The charging, discharging, rectification and filtering of the capacitor, and even its phase shifting, reactance and other functions, are all the storage functions of the capacitor at work. The reason why the capacitor can store charge is realized by the strong mutual attraction between positive and negative charges. When charging a capacitor, people introduce positive charges into the positive plate through the power supply, and negative charges into the negative plate of the capacitor. But the positive and negative charges can’t get together again because there is a layer of insulating mold blocking them. The larger and thinner the diaphragm, the greater the gravitational force. The more charge is stored. The positive and negative charges are attracted between the ten plates, but if you provide it with an external circuit, they will be able to combine with each other through this external circuit, that is, discharge. After all, they are one high and one low hemp. In appearance, the capacitor is like a reservoir. It can graphically illustrate the role of its rectifying wave.
25. After the filter capacitor is fully charged, then discharge the back circuit and then in the charge and discharge cycle? Is the Zener diode breakdown or non-breakdown?
In fact, what you said is quite right. It is such a working process in the circuit, but it is related to the frequency of the signal. First of all, it depends on what you want to put the capacitor in the circuit. When it is used as a filter, it must The frequency signal is filtered to the ground, such as the capacitor at the front end of the chip power supply, and some are decoupling. The phenomenon you said is like the filter capacitor before the voltage regulator is turned off and the filter capacitor of the switching power supply output.
Regarding the Zener tube, let me give you an example. If there is a 5V Zener tube, when the voltage is lower than 5V, the voltage will be equal to its own voltage. When the voltage is higher than 5V, the Zener tube will stabilize the voltage. 5V, the excess voltage turns the voltage regulator off and breaks down the channel first.
26. What is the specific meaning of capacitive coupling? Is it different from filtering?
Coupling refers to the process of signal transmission from the first stage to the second stage, and usually refers to AC coupling when it is not specified. Decoupling refers to taking further filtering measures to the power supply to remove the influence of mutual interference between the two levels of signals through the power supply. The coupling constant refers to the time constant corresponding to the product of the coupling capacitance value and the second-stage input impedance value.
Decoupling has three purposes: 1. Remove the high-frequency ripple in the power supply, and cut off the high-frequency signal of the multi-stage amplifier through the crosstalk path of the power supply; 2. When the large signal is working, the circuit’s demand for the power supply increases, causing the power supply Fluctuations, through decoupling to reduce the impact of power fluctuations on the input stage/high voltage gain stage during large signals; 3. Form a floating ground or floating power supply, and complete the coordinated matching of various parts of the ground or power supply in a complex system
The high frequency switching noise generated by the active device during switching will propagate along the power line. The main function of the decoupling capacitor is to provide a local DC power supply to the active device to reduce the propagation of switching noise on the board and to guide the noise to the ground.
27. What is the function of the capacitor? I only know that filtering is to filter out the AC signal, thank you for your answer.
Not just filtering, it’s all for you:
1. Capacitors are mainly used in AC circuits and pulse circuits. In DC circuits, capacitors generally function to block direct current.
2. The capacitor neither generates nor consumes energy, and is an energy storage element.
3. The capacitor is an important device to improve the power factor in the power system; in the electronic circuit, it is the main component to obtain the functions of oscillation, filtering, phase shift, bypass, and coupling.
4. Because the loads used in industry are mainly motor inductive loads, the capacitive load must be paralleled to balance the power grid.
5. On the grounding line, why some have to pass the capacitor before grounding?
Answer: In the DC circuit, it is anti-interference. The interference pulse is grounded through the capacitor (this time the function is to block the direct current-the potential relationship in the circuit); in the AC circuit, there is also the grounding through the capacitor, and the capacity is generally small. Anti-interference and potential isolation.
28. How does the capacitor play a filtering role in the circuit? The capacitor is open circuit, is it charging the capacitor when the alternating current passes through it? Are the capacitors in parallel or in series?
The capacitive reactance of the capacitor changes with the frequency of the alternating current applied at both ends, Z=1/2*3.14*FC. Set different capacitance values according to which frequency current needs to be filtered. In this way, the unnecessary current can be led to the ground, and the filtering is completed. And for the current of the required frequency, the capacitor is a path or the impedance is very small. When alternating current is passed, it is a process of repeated charging and discharging.
29. What are the functions of decoupling capacitors, filter capacitors, and bypass capacitors? What are the differences and connections between them?
For example, the emitter of a transistor amplifier has a self-biased resistor, which at the same time causes the signal to generate a voltage drop and feed it back to the input to form an input and output signal coupling. This resistor is the element that generates the coupling. If a capacitor is connected in parallel across the resistor Since a capacitor of appropriate capacity has a smaller impedance to the AC signal (this needs to be calculated), this reduces the coupling effect produced by the resistance, so this capacitor is called a decoupling capacitor.
Bypass capacitor is not a theoretical concept, but a practical method that is often used. In the 1950s and 1960s, the term had its own meaning, and it is not used much now. The electron tube or transistor needs to be biased, which is the DC power supply condition that determines the operating point. For example, the grid of an electron tube often requires a negative voltage relative to the cathode. In order to work under a DC power supply, a resistor is connected in series between the cathode and the ground, and the plate current is used to form the positive potential of the cathode to the ground, and the grid is DC grounded. This biasing technique is called “self-biasing”, but for (AC) signals, it is also a negative feedback. In order to eliminate this effect, a sufficiently large point capacitance is connected in parallel to this resistor, which is called side-by-side. Road capacitance. Later, some materials extended it to similar situations.
The filter capacitor is better understood. The capacitor has the effect of passing AC and blocking DC. Filtering means that I can filter out the AC signal of a certain frequency by selecting different filter capacitors, leaving the desired frequency signal.
30. Is the coupling capacitor a decoupling capacitor?
It is completely different. The coupling capacitor is for signal transmission, and the decoupling capacitor is for reducing interference.
31. What is the principle of capacitive decoupling?
If the DC circuit enters the AC signal or the self-excited feedback of the AC amplifier circuit, it will have undesirable consequences! In order to prevent the AC component from being coupled and amplified step by step, a capacitor is set between the stages to make it flow back to the ground! This capacitor is the decoupling capacitor!
32. What is the difference between coupling and decoupling, what are the roles of coupling capacitor and decoupling capacitor, how to place it in the circuit, and what are the principles?
The function of the coupling capacitor is to transmit the AC signal of the previous stage to the next stage!
The position of the coupling capacitor is connected across the output of the previous stage and the input of the latter stage!
The function of the decoupling capacitor is to short-circuit the unprofitable AC signal from the amplifier stage to the ground!
The location of the decoupling capacitor is between the ground of a certain input stage!
33. How to distinguish whether the capacitor in the electronic circuit is a filter capacitor or a bypass capacitor?
The filter capacitor is in the power circuit; the bypass capacitor is in the signal circuit; in fact, the function is basically the same. The filter capacitor: bypasses or filters out the pulsating current components and plays the role of charging and discharging. Bypass capacitor: filter or bypass high frequency or low frequency components in the circuit.
34. Does any expert know the difference between decoupling capacitors and bypass capacitors?
Bypass capacitor is not a theoretical concept, but a practical method that is often used. Electron tubes or transistors need to be biased, which is to determine the DC power supply conditions of the operating point. For example, the grid of an electron tube often requires a negative voltage relative to the cathode. In order to work under a DC power supply, a resistor is connected in series between the cathode and the ground, and the plate current is used to form the positive potential of the cathode to the ground, and the grid is DC grounded. This biasing technique is called “self-biasing”, but for (AC) signals, it is also a negative feedback. In order to eliminate this effect, a sufficiently large point capacitance is connected in parallel to this resistor, which is called side-by-side. Road capacitance.
The decoupling capacitor has two functions between the power supply of the integrated circuit and the ground: on the one hand, it is the energy storage capacitor of the integrated circuit, and on the other hand, it bypasses the high-frequency noise of the device. The typical decoupling capacitor value in digital circuits is 0.1μF. The typical value of the distributed inductance of this capacitor is 5μH. The 0.1μF decoupling capacitor has a distributed inductance of 5μH, and its parallel resonance frequency is about 7MHz. That is to say, it has a better decoupling effect for noise below 10MHz, and it has little effect on noise above 40MHz. Capacitors of 1μF and 10μF, and the parallel resonance frequency is above 20MHz, the effect of removing high-frequency noise is better. Every 10 pieces of integrated circuits need to add a charge and discharge capacitor, or an energy storage capacitor, about 10μF is optional. It is best not to use electrolytic capacitors. Electrolytic capacitors are rolled up with two layers of film. This rolled up structure behaves as an inductance at high frequencies. Use tantalum capacitors or polycarbonate capacitors. The selection of decoupling capacitors is not critical, you can press C=1/F, that is, 0.1μF for 10MHz and 0.01μF for 100MHz.
Generally speaking, uf-level capacitors, such as electrolytic capacitors or tantalum capacitors, have larger inductance and smaller resonance frequency, which can pass low-frequency signals better, but show strong inductance for high-frequency signals. The impedance is large, and at the same time, the large capacitor can also act as a local charge pool, which can reduce local interference through the power supply coupling; the capacitor with a capacity of 0.001~0.1uf, generally a ceramic capacitor or a mica capacitor, has a small inductance and a resonance frequency High, low impedance to high-frequency signals, can provide a bypass for high-frequency interference signals, reduce the external coupling interference to this part.
Bypass is to filter out high-frequency clutter or signals carried by the pre-stage or power supply; decoupling is a “small pond” set up to maintain the stable output of the positive output terminal (mainly for the operation of the device), and work in other high currents. Make sure that the fluctuation range of the power supply will not affect the operation of the circuit; one additional point is the so-called coupling: it is the components that transmit signals between the front and rear stages without affecting each other’s static operating points.
The high frequency switching noise generated by the active device during switching will propagate along the power line. The main function of the decoupling capacitor is to provide a local DC power supply to the active device to reduce the propagation of switching noise on the board and to guide the noise to the ground.
From the circuit point of view, there is always a source of driving and a load being driven. If the load capacitance is relatively large, the drive circuit must charge and discharge the capacitance to complete the signal jump. When the rising edge is relatively steep, the current is relatively large, so that the drive current will absorb a large power supply current. The inductance and resistance (especially the inductance on the chip pins will cause bounce). Compared with normal conditions, this current is actually a kind of noise, which will affect the normal operation of the previous stage. This is coupling.
The decoupling capacitor acts as a battery to meet the change of the drive circuit current and avoid mutual coupling interference.
The bypass capacitor is actually decoupled, but the bypass capacitor generally refers to high-frequency bypass, that is, to improve a low-impedance leakage prevention method for high-frequency switching noise. High-frequency bypass capacitors are generally relatively small. According to the resonance frequency, they are generally 0.1u, 0.01u, etc., while decoupling capacitors are generally larger, 10u or greater, depending on the distribution parameters in the circuit and the magnitude of the drive current change.
35. How to distinguish whether the capacitor in the electronic circuit is a filter capacitor or a bypass capacitor?
The filter capacitor is in the power circuit; the bypass capacitor is in the signal circuit; in fact, the function is basically the same. The filter capacitor: bypasses or filters out the pulsating current components and plays the role of charging and discharging. Bypass capacitor: filter or bypass high frequency or low frequency components in the circuit.
36. Experts please tell me: diodes, triodes, capacitors. How does it work in the circuit?
1. The diode plays a role of unidirectional conduction.
2. The triode plays an amplifying role in an analog circuit and a switch in a digital circuit.
3. Capacitors generally play a role in blocking AC and DC, such as filter capacitors, coupling capacitors, etc., and the fundamental purpose is “passing AC and blocking”.
37. Ask the lovely masters! What is the role of the wave filter capacitor in the circuit? Thank you all! ! !
Low-frequency filter capacitors are mainly used for mains filtering or filtering after transformer rectification, and their working frequency is the same as that of mains at 50Hz; while high-frequency filter capacitors are mainly used for filtering after switching power supply rectification, and their working frequency is several thousand Hz to several thousand Hz. Ten thousand Hz. When we use low-frequency filter capacitors in high-frequency circuits, due to the poor high-frequency characteristics of the low-frequency filter capacitors, it has a large internal resistance and a high equivalent inductance during high-frequency charging and discharging. Therefore, in use, a large amount of heat is generated due to frequent polarization of the electrolyte. The higher temperature will vaporize the electrolyte inside the capacitor and increase the pressure in the capacitor, which will eventually cause the capacitor to bulge and burst.
38. Resistance: has the function of up and down voltage. Capacitor: It has the functions of filtering, rectification and energy storage. Diode: It has the function of voltage stabilization and unidirectional current.
39. How does the capacitor compensate for the power factor?
Answer: Because the establishment of the voltage on the capacitor first requires a charging process. With the charging process, the voltage on the capacitor gradually increases, so that there will be a current first and then a process of establishing a voltage. Usually we call the current lead the voltage by 90 degrees (capacitor When there are no resistance and inductance components in the current loop, it is called a pure capacitive circuit). Inductance circuits with coils such as motors and transformers, because the current through the inductance cannot be changed suddenly, it is the opposite of capacitors. It is necessary to establish a voltage at both ends of the coil before there is current (when there is no resistance and capacitance in the inductance current loop, Called pure inductance circuit), the current of the pure inductance circuit lags the voltage by 90 degrees. Since power is voltage multiplied by current, it is generated when the voltage and current are different (for example: when the voltage on the capacitor is at the maximum, the charge is full and the current is 0; when there is voltage on the inductor first, the inductor current is also 0), so , The product (power) obtained is also 0! This is reactive power. Then, the relationship between the voltage and current of the capacitor is just the opposite of the relationship between the voltage and current of the inductor, and the capacitor is used to compensate the reactive power generated by the inductor. This is the principle of reactive power compensation.
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