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Can you answer these questions about using capacitors?



Can you answer these questions about using capacitors?


The positive and negative terminals of voltage source are connected with capacitor in parallel with circuit. When used in rectifier circuit, it has a good filtering effect. It stabilizes voltage.

When used as a battery power supply, it has an AC circuit function, which is equivalent to short-circuiting battery's AC signal, avoiding parasitic oscillations of circuit due to a decrease in battery voltage and an increase in battery internal resistance.


For example, in which circuit can a capacitor be connected in series or in parallel to achieve coupling effect, what is difference between an undischarged capacitor and a discharged capacitor?

In a multi-stage AC amplifier circuit, due to different gain and power of each stage, operating DC bias of each stage is different! If direct coupling between stages will make operating bias of each stage mixed and cannot work normally! Using coupling and DC blocking characteristics of capacitor not only solve problem of AC interstage coupling, but also isolate interstage coupling of offset value, which kills two birds with one stone!< /p>


The two decoupling capacitors in basic amplifier circuit, capacitor + pole and DC + pole, are connected to each other to play role of coupling and isolation. What happens if connection is reversed? role in communication? role of a straight line, why do you want to connect it like that!

If connection is reversed, electrolytic capacitor will leak, which will change DC operating point of circuit, making amplifying circuit abnormal or inoperable.


What is function of a capacitor in an RC link amplifier circuit?

Isolate DC signal so that static operating points of adjacent amplifier circuits are independent of each other and do not interfere with each other.


Can analog circuit amplifiers not use coupling capacitors, but can they be amplified?

The amplifier in book adds a decoupling capacitor between secondary of transformer and triode. The explanation is to pass AC and block DC, and change output of previous stage to input of next stage. so that front and rear stages do not affect. The previous stage is AC. The last stage is also AC, how can they affect each other, I just can’t understand that adding a capacitor is not superfluous.

Can you answer these questions about using capacitors?

You made a mistake. The first stage is indeed AC, but last stage is AC superimposed on DC. The triode needs a DC bias. If there is no DC blocking capacitor, transformer coil will bias DC current of triode. Get around it because inductor is DC.


Coupling capacitor of main amplification circuit, can coupling capacitor be non-polar?

In a basic amplification circuit, coupling capacitor is frequency dependent. At high frequency, a non-polar capacitor is required. It is characterized by relatively stable, high withstand voltage and relatively small volume, but capacitance is not large. .

The widest application is blocking DC through AC, and it is widely used in high frequency AC, bypass, resonant and other circuits that can simply be understood as high frequency paths.

At low frequency, capacitance of non-polar capacitor is relatively large due to low capacitance, so it is necessary to use a polar electrolytic capacitor. Since an electrolyte is added inside, capacitance can be increased. very large, so that low-frequency alternating current passes and direct current is blocked.

However, due to organic medium between internal poles, withstand voltage is limited, and it is mainly used in low-frequency AC circuits, filtering, decoupling, bypass and other circuits, and is simply understood as low-frequency. channels.


What is role of a decoupling capacitor?

In amplification circuit, high-frequency AC signal can flow smoothly through circuit and be amplified step by step, while DC flow is blocked within each stage by a DC coupling and blocking capacitor function. .


Why does a battery-powered circuit charge and discharge a capacitor, which acts as a delay?

Capacitors accumulate charges. You can think of it like a glass of water. Charging and discharging is charging and discharging of water. During charging, voltage rises slowly. On contrary, you only need to define voltage at both ends of capacitor to implement delay.

As with charging, voltage across capacitor is zero at beginning, and as charging time increases, voltage gradually rises to voltage you set to control switching of circuit.

Of course, discharge can also be used in reverse. The delay time is related to capacitance of capacitor, leakage of capacitor, charging resistance and voltage, and sometimes load resistance is also taken into account.


Resistance-capacitive lightThe IDE is designed to use coupling and DC blocking characteristics of capacitor to prevent crosstalk and instability at operating point of DC component between front and rear stages.


The RC coupling amplifier circuit can only amplify AC signals, not DC signals, right or wrong?

Yes, a capacitor is an electronic component that blocks DC and resists AC, so an RC coupling amplifier circuit can only amplify AC signals, while a feedforward amplifier circuit is used to amplify DC signals.


How can I tell difference between a coupling capacitor and a blocking capacitor in an amplifier circuit?

The negative pole of bypass capacitor is not grounded, but connected to input of next stage, and negative pole of bypass capacitor is grounded.


How to choose capacitive coupling for an op amp AC multistage amplifier circuit?

It's actually very simple, ordinary ceramic capacitors can be made! If effect is good, you can choose a tantalum capacitor. According to frequency range of your input signal, you can choose a capacitor with a capacitance of 103 or 104. For a lower frequency AC signal, you can choose an electrolytic capacitor of about 22uF.


The amplifier circuit uses a feed forward and feedback network is a pure resistance network. Why can circuit only produce high frequency oscillations?

The fluctuations are due to phase shift of closed loop reaching 180 degrees, and loop gain at this time is greater than zero. Using a pure resistor circuit as a feedback circuit will definitely not introduce phase shift, so all of phase shift comes from open circuit amplifier.

A feed-forward open-loop amplifier will not have a capacitive element between stages that causes phase shift, so internal capacitance of transistor or MOS tube can be cause of phase shift. These capacitances are equal to fF, maximum level of pF Capacitors, resonant frequency of circuit formed by these capacitors, and equivalent resistance of circuit are quite high.

Therefore, amplifier uses a direct connection, and feedback network is a purely resistive network that can only produce high frequency oscillations.


The bandwidth of RC coupling amplifier circuit refers to (difference between upper limit cutoff frequency and lower limit cutoff frequency). The cutoff frequency of upper limit of RC coupling amplifier circuit refers to (with increasing frequency, gain decreases to 0.707 times, that isb frequency at -3dB) The lower limit cutoff frequency of RC amplifier circuit refers to (when frequency decreases, gain drops to 0.707 times original, that is, frequency at -3dB).

The upper cutoff frequency of RC coupling amplifier circuit is mainly affected by (transistor junction capacitance, distributed circuit capacitance), and lower cutoff frequency of RC coupling amplifier circuit is mainly affected by (DC blocking capacitor and bypass) capacitance .


How is an electrolytic capacitor connected to next stage in a multistage amplifier circuit? Does capacitor's DC characteristic block? How is it transmitted? Also, capacitor must be connected through collector of triode, and why not through emitter?

AC amplifiers use electrolytic capacitors, and direction of AC current changes periodically. Is it possible to turn on triode normally?

Isn't collector of an NPN transistor going from C to B, how does its current flow to base of next stage transistor?

All amplifiers that use electrolytic capacitors as coupling are AC amplifiers. Electrolytic capacitors are used here for "coupling and isolating DC". Which pole of triode is output depends on shape of circuit, and there is both.


1. How to evaluate output impedance of first stage amplifier and input impedance of second stage amplifier?

2. When amplitude of signal source is too high, what happens at outputs of two-stage amplifiers?

3. Shake amplifier's input end with your hand and look at amplifier's output end to see if there's something there? what is reason?

1. The input impedance of second stage amplifier is equal to output impedance of first stage amplifier.

2. Distortion.

3. Mess, human body induction


Can capacitors play a bonding role? For example, in which circuit can a capacitor be connected in series or in parallel to achieve coupling effect, what is difference between a non-discharging capacitor and a discharging capacitor?

In a multi-stage AC amplification circuit, due to different gain and power of each stage, operating DC bias of each stage is different! If direct coupling between stages will make operating bias of each stage mixed and cannot work properly! Using coupling and DC blocking characteristics of capacitor not only solve problem of AC coupling between stages, but also isolate coupling of offset value between stages, killing two birds with one stone!


Capacity is charging and discharging. Then how to use thecapacitors and discharging to understand filtering, decoupling, shunting...

Capacitors block DC and communicate with AC. DC blocking is easy to understand, but AC blocking is not easy. If you understand AC, you will be able to understand filtering, decoupling, and bypassing.

The capacitance is either charging or discharging, which is good, but direction of alternating current changes alternately, and amplitude also changes periodically, whole changing picture is a sinusoidal curve.

The capacitor is connected to AC circuit by periodically changing AC voltage, it is also periodically charged and discharged. There is a charging and discharging current in circuit. Except that phase of this charging and discharging current is 90 degrees ahead of voltage, shape is exactly same as voltage, which is equivalent to an alternating current passing through a capacitor.

It is different from alternating current passing through a resistance. An alternating current passing through resistance consumes electrical energy (heating) on ​​the resistance, and passing through capacitor, it only exchanges energy with power source. When charging, power supply gives energy to capacitor, and when discharging, capacitor returns electrical energy to power supply, so power generated by voltage times current is called reactive power here.

It needs to be clarified that when a capacitor is connected to an AC circuit, flowing electrons (current) do not actually race through insulating layer, but a current is generated in circuit. This is due to fact that in circuit reverse discharge and direct charge go in same direction.

Direct discharge and reverse charge go in same direction, like in a relay race, one team goes through positive half cycle of AC, and other team takes over and continues to run negative half cycle of AC. alternating current.

Realizing that capacitor interacts with alternating current, it is clear that you need to shunt variable component to ground and complete filter.


How to use shunt capacitors, filter capacitors and decoupling capacitors? Several examples can be given.

The capacitors with these three names are actually filters, but they are used in different circuits, and their names and applications are different.

Filter Capacitor: This is capacitor we usually use after rectifying power. It is a capacitor that rectifies AC rectifier circuit into pulsating DC current and smooths it out when charging and discharging. Usually it is a high capacity electrolytic capacitor. , at microfarad level.

Bypass Capacitor: Used to filter high frequency components of input signal. Mainly used for high frequency noise filtering. Usually used farfor capacitors and polyester capacitors. The capacitance is small, at level of picofarads.

Decoupling Capacitor: It takes output signal interference as a filtering object. Decoupling Capacitor is equivalent to a battery. By using it for charging and discharging, amplified signal will not be disturbed by a sudden change in current. Its bandwidth depends on frequency of signal and degree of ripple suppression.


What are coupling capacitors and decoupling capacitors? What are their characteristics and functions?

Coupling capacitors are used to carry AC signals and are connected to line. Decoupling capacitors are used to remove useless AC signals. One end is connected to line and other end is grounded.


What are functions of capacitors, under what circumstances can capacitive coupling be used, and under what circumstances can capacitor filtering be used?

Ultimately eighteen martial arts capacitors in a circuit is two! Charging charging! Discharging charge!

Its characteristic is to pass through alternating current and block direct current! After an alternating voltage is applied to both ends of capacitor, it will continue to charge and discharge at a variable frequency of current! At this time, an alternating current of same frequency occurs in circuit! This is a characteristic of movement of a capacitor!

At appropriate frequency, capacitor can be seen as path to circuit! The AC output of previous stage can be transferred to subsequent circuit via a capacitor!

But for direct current it is isolated! Because when voltage at both ends of charge is equal to voltage in circuit, there will be no more charging current!

When it affects front and rear AC signaling, it's a link! When it acts on filtering of fluctuation components and useless AC components, it is filtering!


As we all know, capacitive filter of a rectifier circuit must use its charge and discharge; but sometimes filter needs to use different capacitor capacitance reactance for different frequency signals like bypass capacitor so which one to use when analyzing capacitor filter Angular analysis ah?

Actually, no matter what statement is, theory of using charge and discharge is more general, and theory of using capacitive reactance is deeper. The function of capacitance is to use its charge characteristics. and discharge. In addition to any components, a large capacitor is used to filter low frequencies, and a small capacitor is used to filter high frequencies. In theory, filtering in low-frequency rectifier circuit and bypassing high-frequency oneoval, and they all use difference in capacitive reactance.


How does a capacitor perform functions of charging and discharging, rectifying and filtering?

Charging, discharging, rectifying and filtering capacitors, even phase shift, reactance and other functions are all capacitor storage functions.

The reason a capacitor can store charge is because of strong mutual attraction between positive and negative charges.

When charging a capacitor, people transfer positive charges to positive plate through power supply, and negative charges to negative plate of capacitor.

But positive and negative charges can't get together because a layer of insulating mold blocks them. The larger and thinner diaphragm, stronger attraction.

The more charges stored. Positive and negative charges are attracted between ten plates, but if you supply it with an external circuit, they will connect with this external circuit, that is, they will be discharged.

After all, they have one tall and one short. Figuratively speaking, a condenser is like a reservoir for storing water. It can vividly illustrate its rectifying and filtering function.


After filter capacitor is fully charged, discharge return circuit and then cycle charge and discharge? Zener diode breaks voltage regulator or not?

Actually you are right. This is such a workflow in circuit, but it has something to do with frequency of signal. First of all it depends on what kind of capacitor you want to use in circuit for. When it is used as a filter, it filters a certain frequency signal to ground, such as capacitor at front end of chip power supply, and some decoupling. The phenomenon you mentioned is similar to filter capacitor before regulator is turned off, and filter capacitor is brought out by switching power supply.

Let me give you an example with a Zener tube. If there is a 5V Zener tube, when voltage is less than 5V, voltage is equal to its own voltage. Stable to 5V, overvoltage cuts off voltage. regulation and first breaks channel


What is specific meaning of capacitive coupling? Is this different from filtering?

Connection refers to process of signal transmission from first stage to second stage, and usually refers to an AC connection unless otherwise noted.

Decoupling refers to taking additional measures to filter power supply to eliminate effect of mutual signal interference between two stages through power supply.

Coupling constant refers to time constant corresponding to product of coupling capacitance value and second stage input impedance value.

trong>Decoupling has three goals:

  • Remove high-frequency ripple in power supply, and cut off high-frequency signal of multistage amplifier through crosstalk path of power supply;

  • When a large signal is operating, power consumption of circuit is increased, causing power fluctuations, and effect of power fluctuations on high voltage input/amp stage during large signals is reduced by decoupling;

  • Form an overhead ground or overhead power supply, and complete coordination and matching of various parts of ground wire or power supply in a complex system.

  • The high frequency switching noise generated by active device during switching will propagate along power line. The main function of decoupling capacitor is to provide local DC power to active device in order to reduce propagation of switching noise to board and steering noise to ground.


    What is a capacitor for? I only know about filtering, which is supposed to filter out AC signals.

    It's not just filtering, it's all for you:

    1.Capacitors are mainly used in AC circuits and impulse circuits. In DC circuits, capacitors usually play role of DC blocking.

    2. Capacitors do not produce or consume energy, but are energy storage components.

    3. The capacitor is an important device for improving power factor in power system; The circuit is main component to obtain effects of generation, filtering, phase shift, bypass, coupling, etc.

    4. Since load used in industry is mainly inductive load of motor, it is necessary to balance power system in parallel with capacitive load.

    5. Why on ground line do some have to go through a capacitor before grounding?

    In a DC circuit, this is interference protection. The noise pulse is grounded through capacitor. In this case, main function is DC blocking - ratio of potentials in circuit; Interference protection and potential isolation. .

    6. What is capacitor compensation power factor?

    Because charging process is required to establish voltage on capacitor first. During charging process, voltage on capacitor gradually increases, so that there will be a current first, and then voltage setting process. We usually call current 90 degrees ahead of voltage. When in a capacitive current loop does not have resistors and inductors, it is called a purely capacitive circuit.

    Inductor circuits with coils, such as motors and transformers, because current through an inductor cannot suddenly change, it is exact opposite of a capacitor. He mustn set voltage at both ends of coil before current flows. In an inductor current circuit, there is no resistance and no current. When a capacitor is used, it is called a pure inductance circuit, and current of pure inductance circuit lags voltage by 90 degrees.

    Because power is product of voltage and current, when voltage and current are different, for example: when voltage across capacitor is largest, electricity is fully charged and current is 0; when there is voltage across inductor, inductor current is also 0. So resulting product (power) is also 0! It's reactive.

    Then relationship between voltage and current of capacitor is directly opposite to relationship between voltage and current of inductor, and capacitor is used to compensate for reactive power generated by inductor, which is principle of reactive power compensation.


    How does a capacitor act as a filter in a circuit? The capacitor is open, does it charge capacitor when AC current is passed through it? Are capacitors connected in parallel or in series?

    The capacitance reactance of a capacitor varies with frequency of AC applied to both ends, Z=1/2*3.14*FC, set different capacitance values, depending on which frequency current needs to be filtered.

    In this way, unnecessary current can be driven to ground, and filtering is completed. A capacitor is connected for a current of desired frequency, or impedance is very small. When an alternating current passes, it is a process of repeated charging and discharging.


    Decoupling capacitors, filter capacitors, bypass capacitors, what are their functions, as well as differences and relationships between them

    For example, emitter of a transistor amplifier has an auto-bias resistor, which at same time causes signal to generate a voltage drop and return to input terminal to form an input-output signal coupling. This resistor is component that creates coupling. If resistor is connected in parallel, capacitor is called a decoupling capacitor because a capacitor of appropriate capacitance has less resistance to AC signal, which reduces coupling effect of resistor.

    Vacuum tubes or transistors must be biased to determine operating point DC supply conditions. For example, gate of a vacuum tube is often required to have a negative voltage with respect to cathode. resistor, use plate current to form a positive cathode potential to ground, and grid is DC grounded. This biasing method is called "self-biasing", but for (AC) signals, this is also negative feedback at. To eliminate this effect, connect a point in parallel with this resistor capacitance of a sufficiently large capacity, which is calledshunt capacitor. Later, in some materials, it was extended to similar situations.

    The filter capacitor is more clear. Capacitors allow alternating current to pass and block direct current. Filtering means that I can filter AC signals of a certain frequency by choosing different filter capacitors, leaving a signal of desired frequency.


    Is coupling capacitor a decoupling capacitor?

    This is completely different, a coupling capacitor for signal transmission, and a decoupling capacitor for noise reduction.


    What is principle of capacitive decoupling?

    The DC circuit is interrupted by AC signal, or self-excited feedback of AC amplifier circuit will have adverse effects! To prevent AC component from coupling and gradually amplifying, a capacitor is placed between stages to force it to flow back to ground! A capacitor is a capacitance lotus root retreat!


    What is difference between bond and decoupling? What are functions of isolation and decoupling capacitors? How to place them in a chain?

    The function of coupling capacitor is to transfer alternating signal of previous stage to next stage!

    The coupling capacitor is connected between output of previous stage and input of last stage!

    The function of decoupling capacitor is to short out useless AC signal that is passed between amplifier stages to ground!

    The decoupling capacitor is between front end ground!


    How can I tell if a capacitor in an electronic circuit is a filter capacitor or a bypass capacitor?

    The filter capacitor is in power circuit and shunt capacitor is in signal circuit. In fact, function is basically same. Filter capacitor: bypasses or filters out ripple current and acts as a charge Shunt capacitor: filters or blocks high or low frequency components in circuit .


    What is difference between a decoupling capacitor and a shunt capacitor?

    The bypass capacitor is not a theoretical concept, but a commonly used practical method. The vacuum tube or transistor must be biased to determine state of operating point DC power supply.

    For example, grid of a vacuum tube often needs to have a negative voltage with respect to cathode. To operate from a DC source, a resistor is connected in series between cathode and ground, and current is used to form positive potential of cathode to ground, while grid is a DC ground, this bias methodcalled "self-replacement", but for signals (AC) it is also negative feedback. To eliminate this effect, a sufficiently large point capacitance, called a shunt capacitor, is connected in parallel with this resistor.

    The decoupling capacitor has two functions between power supply and ground of integrated circuit: on one hand, it is a capacitor for storing energy of integrated circuit, on other hand, it bypasses high-frequency noise. The decoupling capacitor has a capacitance of 0.1 uF. The typical distributed inductance of this capacitor is 5 µH.

    The 0.1uF decoupling capacitor has a distributed inductance of 5uH, and its parallel resonant frequency is about 7MHz, that is, it has a good decoupling effect for noise below 10MHz and has little effect on noise above 40MHz.

    1uF, 10uF capacitors, parallel resonance frequency is higher than 20MHz, and high-frequency noise removal effect is better. Every 10 or so integrated circuits need to add a charge-discharge capacitor or energy storage capacitor, which can be about 10uF.

    It is better not to use electrolytic capacitors. Electrolytic capacitors are rolled up with two layers of film. This folded structure behaves like an inductor at high frequencies. To use tantalum capacitors or polycarbonate capacitors, choice of decoupling capacitors is not important. Strictly according to C \u003d 1 / F, that is, 0.1 μF is taken at 10 MHz, and 0.01 μF is taken at 100 MHz.

    Generally speaking, a uF capacitor, like an electrolytic capacitor or a tantalum capacitor, has a large inductance and a small resonant frequency, which is better for low frequency signals and stronger for high frequency signals. , large impedance, at same time, large capacitance can also play role of a local charge pool, which can reduce local interference associated with power supply.

    0.001~0.1uF capacitors are usually ceramic or mica capacitors. They have low inductance, high resonant frequency and low resistance to high frequency signals. They can bypass high frequency noise and interference. reduce external interference. Local communication interferes.

    The bypass is designed to filter out high frequency interference or signals carried by front stage or power supply; When working with high current, make sure that fluctuation range of power supply will not affect operation of circuit; Addition 1It's so-called coupling: it is a component that transmits signals between front and rear stages without affecting each other's static operating points.

    The high frequency switching noise generated by active device during switching will propagate along power line. The main function of decoupling capacitor is to provide local DC power to active device in order to reduce theTransfer of switching noise to board and steering noise to ground.

    From a circuit point of view, there is always a source of excitation and a load. If load capacitance is relatively large, drive circuit must charge and discharge capacitance to complete signal transition. When rising edge is relatively steep, current is relatively large.

    Current controlled in this way will absorb a large current from power supply. Due to inductance and resistance in circuit (especially inductance at IC pins it will reflect) this current is actually noise which will affect normal operation of front stage. This is a clutch.

    The decoupling capacitor should act as a battery to match change in drive circuit current and avoid communication interference.

    A decoupling capacitor is actually a decoupling capacitor, but a bypass capacitor is typically a high frequency bypass, meaning it provides a low impedance discharge path for high frequency switching noise.

    High frequency bypass capacitors are generally small, typically 0.1 u, 0.01 u, etc. depending on resonant frequency, while decoupling capacitors are typically relatively large, 10 u or more, depending on distribution parameters in circuit and changes in drive current to be sure.


    How do diodes, transistors and capacitors work in circuits?

    1. The diode acts as a one-way conduction.

    2. The triode acts as an amplifier in an analog circuit and a switch in a digital circuit.

    3. Generally speaking, capacitors play role of AC transmission and DC blocking, such as filter capacitors, coupling capacitors, etc., and main purpose is "DC coupling and isolation".


    What role does filter capacitor play in circuit?

    Low-pass filter capacitors are mainly used for network filtering or filtering after transformer rectification from Hz to tens of thousands of Hz.

    When we use low-frequency filter capacitors for high-frequency circuits, due to poor high-frequency performance of low-frequency filter capacitors, their internal resistance is relatively large during high-frequency charging and discharging, and their equivalent inductance is relatively high.

    Therefore, during use, a large amount of heat will be generated due to frequent polarization of electrolyte, and a higher temperature will cause electrolyte inside capacitor to evaporate, and pressure inside capacitor will increase, which will eventually cause capacitor to swell and burst.