In the DC circuit, the capacitor is equivalent to the disconnection. The capacitor is a storage charge element, is the most commonly used one of the electronic components.
This was from the capacitor structure on the start. Most simple capacitor is made on the both ends of the plate and the intermediate insulating dielectric (including air) [1] constitute. Energized, the plate charged, forming a voltage (potential difference), but due to the insulating material of the middle, so the entire capacitor is not electrically conductive. However, such a situation is a prerequisite of the not exceed the threshold voltage (breakdown voltage) of the capacitor under. We know, no substances are relatively insulated, when the material both ends of the voltage is increased to a certain extent, the material can be electrically conductive, we call this voltage is called the breakdown voltage. The capacitor is no exception, after the capacitor is the breakdown is not an insulator. However, at the secondary level, this voltage in the circuit is not done so in the breakdown voltage can be used as an insulator see.
However, in an AC circuit, because the direction of the current time as a function of changes. The capacitor charge-discharge process of the time, this time, a changing electric field is formed between the plates, while the electric field is also a function of change over time. In fact, the current through the field in the form adopted in between the capacitors.
In secondary schools, there is a saying called pass AC resistive DC is the capacitance of this nature.
The role of capacitance:
1) bypass
Bypass capacitor is an energy storage device to provide energy for local devices, which enables the output of the regulator homogenization, reducing the load demand. Like small rechargeable battery, bypass capacitor can be charged to the device to discharge. To minimize impedance bypass capacitor as close as possible to the load device powered power supply pin and ground pins. This can be well prevented the elevation of the ground potential caused by the input value is too large, and noise. The ground potential is connected in a voltage drop when a large current glitches.
2) decoupling
Decoupling, also known as decoupling. From the circuit can always be zone is divided into the drive source and the driven load. If the load capacitance is relatively large, the drive circuit capacitor charging should be discharge, to complete the transition of the signal at the rising edge of the steep, relatively large current, current to drive so it will absorb a lot of supply current, the circuit the inductance and resistance (especially on the chip pin inductance, will produce rebound), such a current phase for the normal situation is actually a kind of noise, will affect the normal working of the previous stage, which is called the "coupled" .
Decoupling capacitor is to play the role of a "battery", to meet a change in drive circuit current, to avoid mutual coupling between the interference.
Bypass capacitor and decoupling capacitor combination will be easier to understand. Actual bypass capacitor is decoupled, just bypass capacitor generally refers to the high-frequency bypass to improve high-frequency switching noise is a low impedance to vent anti pathway. Frequency bypass capacitor are generally relatively small, and generally according to the resonant frequency such as 0.1μF, 0.01μF; away coupling capacitor is generally large, it may be 10μF or greater, according distributed parameter circuit, and change the size of the drive current to determine. The bypass is the interference in the input signal as filtered object Decoupling of the output signal of the interference as filtered object, and to prevent return the power of an interference signal. This should be their essential difference.
3) filtering
(Assuming said capacitor is pure capacitance), the greater the capacitance, the smaller the impedance, the higher frequency by theory. But in fact most of the more than 1μF capacitance electrolytic capacitors, the inductance component, high frequency instead impedance increases. Sometimes see a larger electrolytic capacitor manufacturer in parallel with a capacitance of a small capacitor, this time a large capacitor through the low-frequency, small capacitor through high frequency. The capacitance of the role is to pass a high impedance low-pass high-frequency resistance low frequency. Higher capacitance increases the low frequency, the easier to pass. Specific filtering, large capacitors (1000μF) low-frequency filter, small capacitance (20pF) high-frequency filter. Had friends vividly than the filter capacitor as "reservoirs". Since both ends of the capacitor voltage is not mutation Therefore, the higher the frequency the greater the attenuation can be very image of the said capacitor like a pond, not caused by changes in the water due to the addition of a few drops of water or evaporation. It converted to voltage changes in the current changes, the higher the frequency, the greater the peak current, so that the buffer voltage. Filtering is charging, the discharge process.
4) Energy Storage
The energy storage capacitor charge is collected through the rectifier , and the stored energy is transmitted via the inverter leads to the power supply output terminal. The voltage rating of 40 ~ 450VDC, capacitance values between 220 ~ 150 000μF aluminum electrolytic capacitors (such as EPCOS B43504 or B43505) is more commonly used. According to the different power requirements, the device is sometimes used in the form of series, parallel, or combinations thereof, and the power level exceeds the power of 10KW, usually larger tank shaped spiral terminal capacitor.
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