What are capacitance charging and discharge?
The positive pole of the capacitance is connected to the positive pole of the power supply, and the negative pole of the capacitance is connected to the negative pole of the power supply at the same time. Capacitors will be charged in a very short period of time. After charging, the capacitance is essentially equal to a battery. At this time, the positive pole of the battery is the positive pole of the capacitance, and the negative pole of the battery is the negative pole of the capacitance.
The capacitance is physically composed of two conductors and an insulating layer located in them. Two electrodes are drawn from the two conductors, and the positive and negative electrodes of the capacitance are corresponding to each other. The insulation layer is usually very thin, when the positive pole of the capacitance is connected to the positive pole of the power supply (such as dry battery), and the negative pole of the capacitance is connected to the negative pole of the power supply, the current in the capacitance will "flow" through the sheet conductor of the positive electrode of the capacitance, and the negative charge will be concentrated in the flake conductor of the negative pole of the capacitance, and a electrostatic field will be formed between the two conductors.
A demonstration diagram verifying that capacitors can store energy and discharge is shown in figure 1.
First of all, take a large capacity of capacitance, the use of adjustable power supply (desirable 5V) or battery (should be greater than 3V) for capacitance charging, and then disconnect the adjustable power supply or battery, take a light-emitting diode, with the positive and negative electrodes of the light-emitting diode touch the capacitance charge positive and negative electrodes, you can see that the light-emitting diode will be lit, and then the brightness will weaken rapidly until it is completely extinguished. At this time, if the voltage of capacitance after discharge is measured by multimeter immediately, a certain residual voltage can still be observed by multimeter.
According to the fact that the light-emitting diode flashes out, we can draw two conclusions: one is that the electric field has energy (the light energy emitted by the light-emitting diode is stored in figure 3 ≤ 6 to verify that the capacitance can store energy and discharge the energy in the capacitance; second, the energy stored by the capacitance is limited, otherwise the light-emitting diode should continue to emit light. The amount of energy stored by capacitors is closely related to its capacity. Obviously, the larger the capacity, the more energy the capacitance stores.
The charging and discharging process of capacitance itself is very easy to understand. This directly leads us to ignore the charge and discharge of capacitors when we learn the basic characteristics of capacitors is also a time-consuming process. It is precisely the time consumed in the process of charging and discharging, which is flexibly applied to all kinds of circuits, and realizes the circuit function which is difficult for many ordinary readers to understand but is very important. Please do not ignore the use of capacitance charge and discharge time in the circuit, which is a hindrance to the vast majority of maintenance personnel and amateurs in understanding the principle of the circuit.
The main capacitance is one of the largest components in ATX power supply. It plays a role in filtering and storing electric energy. The 310V high voltage obtained after full wave rectifier at both ends of the main capacitance behind the full bridge should be avoided by its discharge injury during maintenance. The 310V high voltage at both ends of the main capacitor decreases with the time after the ATX power supply is cut off, which is often used as the basis for judging whether the auxiliary power supply is starting or not. This is because a good auxiliary power supply will continue to work for a period of time even after cutting off the 220V AC power supply, which will dramatically consume the electricity stored in the main capacitor. After the measured results, the normal auxiliary power supply will consume the power on the main capacitance in about 5 s, so that the voltage at both ends of the main capacitance will be rapidly reduced to single digits. If the voltage on the main capacitance cannot be reduced for a long time after cutting off the 220V AC power supply (which cannot be reduced by half within 30s), the auxiliary power supply is faulty.
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