What is the principle of capacitor charging and discharging, and how to understand it?

The capacitor is just connected to the circuit (originally not charged), the switch is closed, and it is charged, and after a while, it becomes charged.

After disconnecting, it does not contact with the outside world, and the power remains unchanged, but after a while, the power will always decrease, which is equivalent to discharging; Originally, it was charged, connected to the loop, discharged, and the amount of electricity became less.

In general, a capacitor is equivalent to an open circuit. Considering the current situation, DC must be open (regardless of the current size); Low-frequency AC is also an open circuit, and only high-frequency AC is the path, regardless of the magnitude of the current.

Charging: Because there is a potential difference between the positive and negative poles of the power supply, the charge moves directionally to the plate of the capacitor under the action of the electric field force to charge, with the increase of the charged charge, the combined electric field decreases, the charging current decreases, the magnetic field can decrease, and the electric field can increase by ......

Extended Materials. The switch of the DC power supply is closed to charge the capacitor; To disconnect the switch, the capacitor must be connected to the discharge resistor to discharge, otherwise it cannot be discharged. The capacitor connected to the AC circuit is equivalent to the path, and the capacitor connected to the DC circuit is equivalent to the open circuit.

In general electronic circuits, capacitors are commonly used to achieve bypass, coupling, filtering, oscillation, phase shift, and waveform transformation, which are the evolution of their charging and discharging functions.

1. Charging: Two metal plates (capacitors) parallel to each other, when the two plates are connected to the positive and negative poles of the battery respectively, the power supply begins to charge the capacitor, the charge on the plate is increasing, and the plate voltage is also rising, until the plate voltage is equal to the battery voltage. If you use a voltmeter to measure the voltage at both ends of the plate, you will notice that the indicated value of the voltmeter keeps rising.

2. Discharge: After the capacitor is fully charged, you connect a small bulb to the two pole plates, the capacitor begins to discharge the bulb, and may light the bulb, as the capacitor continues to discharge, the plate charge is getting less and less, the plate voltage is getting lower and lower, and the bulb is getting darker and darker, until it is completely extinguished, and the charge in the capacitor is discharged.

3. To put it simply, the capacitor charging and discharging process can be compared to storing and discharging water in a pool. The capacitor is charged, and the current flows into the capacitor The voltage at both ends of the capacitor rises and the charge is stored in the capacitor; Tank Water Storage The flow of water flows into the bucket, the water level in the bucket rises, and the water is stored in the bucket. The capacitor discharges, the current flows out of the capacitor, the voltage at both ends of the capacitor drops, and the charge in the capacitor is released; Pool Discharge The water flows out of the bucket, the water level in the bucket drops, and the water in the bucket is released.

The principle of capacitor charging and discharging is as follows:

When the capacitor is powered on, the free electrons of the capacitor board connected to the positive pole of the power supply will move through the power supply to the board connected to the negative pole of the power supply under the force of the electric field. The positive electrode brings positive electricity due to the loss of negative charge, and the negative electrode brings negative electricity due to the acquisition of negative charge.

The positive and negative plates have equal charges of magnitude and opposite signs. The directional motion of the charge forms an electric current. Due to the repulsion of the same charge, the current is maximum at the beginning and then gradually decreases.

During the movement of the charge, the charge stored in the capacitor plate is constantly increasing. When the voltage UC between the two plates of the capacitor is equal to the supply voltage U, the charge stops moving. When the current is i=0, the switch is turned off.

Through the connection of wires, the charge of the positive and negative plates of the capacitor is neutralized. When K is turned off, the positive charge of the capacitor C can move the negative charge, and the negative charge can also move to the positive electrode to neutralize, the charge gradually decreases, the performance current decreases, and the voltage gradually decreases to zero.

Notes:

Since the two poles of the capacitor have the characteristic of residual charge, the capacitor should try to discharge first, otherwise it is prone to electric shock accidents. When dealing with faulty capacitors, the circuit breaker of the capacitor bank and its upper and lower disconnectors should be turned on first.

If fuse protection is used, the fuse tube should be removed first. In this case, although the capacitor bank discharges itself through a discharge resistor, there is still some residual charge. Therefore, manual discharge is necessary.

When discharging, first fix the grounding end of the grounding wire with the grounding grid, then discharge the capacitor several times with the grounding rod until there is no spark and discharge sound, and finally fix the grounding wire.

At the same time, it should also be noted that if the capacitor has an internal disconnection, fuse fuse, or poor wire contact, there may be residual charges between the two electrodes that will not be discharged when automatically or manually discharged.

Therefore, operators or maintenance personnel should wear insulating gloves before touching faulty capacitors and use short-circuit discharge.

A capacitor is a passive device that stores energy in the form of an electric field. Capacitors are able to release stored energy to the circuit when needed. A capacitor consists of two conductive parallel plates, which are filled with an insulating or dielectric substance between the plates.

If the capacitor is connected to the DC power supply, see Figure 3, there is current flowing in the circuit. The two plates each receive an equal number of opposite charges, while the capacitor is being charged, and the potential difference vc between the two ends of the capacitor gradually increases. Once the voltage vc at both ends of the capacitor increases to be equal to the power supply voltage v, vc = v, the capacitor is charged, there is no current flowing in the circuit, and the capacitor charging process is completed.

When the capacitor is charged, there is no current in the circuit where the capacitor is located, and the voltage between the two plates of the capacitor is equal to the charging voltage.

Since no current flows through the capacitor after the capacitor charging process is completed, in a DC circuit, the capacitor can be equivalent to an open circuit or r=, and the voltage vc on the capacitor cannot be abruptly changed. When the connection between the capacitor and the power supply is disconnected, the capacitor is discharged through the resistor RD, and the voltage between the two boards will gradually drop to zero, VC=0, see Figure 4.

When the capacitor is discharged, there is no current in the capacitor circuit. The process of discharging is actually the neutralization of positive and negative charges.

The smaller the capacitance or resistance value, the smaller the time constant, the faster the capacitor can be charged and discharged, and vice versa.

Capacitors are found in almost all electronic circuits, and it can be used as a "fast battery". For example, in the flash of a camera, the capacitor acts as an energy storage element, which quickly releases energy at the moment of flashing.

The two poles are charged with an equal amount of dissonant.

The absolute value of the amount of electricity carried by a plate is called the amount of electricity carried by a capacitor.

Charging and discharging are the basic functions of capacitors.

The process of charging to electrify the capacitor is called charging. At this time, the two poles of the capacitor are always one plate with a positive charge, and the other plate with the same amount of negative electricity. If one plate of the capacitor is connected to the positive pole of the power supply, and the other plate is connected to the negative pole of the power supply, the two plates will each carry the same amount of dissimilar charge.

After charging, there is an electric field between the two plates of the capacitor, and the electrical energy obtained from the power supply is stored in the capacitor collision during the charging process.

The process by which a discharged capacitor loses its charge is known as discharge.

The capacitance power change dq circuit will flow through the power dq, with time dt, current i = dq dt according to the capacitance formula q = cu, dq = cdu

i=dq dt=cdu dt

Voltage-current relationship of linear capacitive elements:

1: Let the voltage and current be a function of time, and now find the relationship between voltage and current. When the voltage between the plates changes, the charge on the plates also changes, and a current is generated in the capacitive element.

This current can be obtained by i=dq dt =c(du dt).

2: The above equation shows that the magnitude and direction of the current depend on the rate of change of voltage versus time.

3: When the voltage increases, du dt 0, then dq dt 0, i 0, the charge on the plate increases, and the capacitor is charged; When the voltage decreases, du dt 0, then dq dt 0, i 0, the charge on the plate decreases, and the capacitor is discharged in the opposite direction. When the voltage does not change with time, du dt=0, then i=0, then the current of the capacitive element is equal to zero, which is equivalent to an open circuit.

Therefore, the capacitive element has the function of blocking DC.

1. In the process of charging and discharging (storing and releasing charge), the capacitor will inevitably generate current in the circuit, but this current does not flow back and forth in the circuit outside the capacitor through the insulator through the insulator, but in the circuit outside the capacitor.

2. The voltage at both ends of the capacitor changes gradually, that is, the capacitor is a little dumb and cannot be mutated. When the capacitor is not charged, the voltage at both ends of the capacitor is zero, and the charging charge increases. The voltage at both ends of the capacitor gradually increases until it is equal to the supply voltage.

When discharging, the voltage at both ends of the capacitor also gradually drops to zero in the closed object.

3. It takes a certain amount of time to complete the charging and discharging of the capacitor car, and the test proves that the process of charging and discharging obeys the change law of the whole line of the index.

The length of charge and discharge time is only related to the capacitance c of the capacitor and the total resistance r of the circuit, usually i=rc is called the time constant of charge and discharge. If the unit of r is and the unit of c is f, then the unit of i is s.

Theoretically, the charging and discharging time of a capacitor is infinitely long, but experiments have proved that the charging or discharging is basically over after (3-5) ID time.

4. The capacitor only has the charging current flow in the circuit at the beginning of the application of DC voltage, and after the end of the point capacitor charging, although there is voltage at both ends of the capacitor, the current in the circuit is zero, which shows that the capacitor has the effect of blocking DC current after charging.

5. When the alternating voltage is added to the capacitor, because the magnitude of the alternating current is constantly changing, the capacitor will continue to charge and discharge, and there will always be current flowing through the circuit, which shows that the capacitor has the effect of passing the alternating current.