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What is Capacitor? 2

已有 1431 次阅读2015-1-8 10:34

Last article we introduced Capacitor's definition and classify.

Now we introduce the function fo capacitor.

In the DC circuit, the capacitor is equivalent to the disconnection. A capacitor is a device capable of storing electric charge, is one of the most commonly used electronic components.

It must start with the structure of the capacitor. The simplest is by the capacitor plates and the intermediate ends of the insulating dielectric (including air) configuration. After energization, the charged plate, forming a voltage (potential difference), but since the intermediate insulating material, so the entire capacitor is not electrically conductive. However, this situation is not exceeded in the threshold voltage of the capacitor (breakdown voltage) of preconditions. We know that any substances are relatively insulated, to increase when the voltage across the substance to a certain extent, the material can be electrically conductive, we call this voltage is called the breakdown voltage. Capacitance is no exception, after the capacitor is the breakdown, it is not an insulator of. However, at the secondary level, this voltage is not seen in the circuit, so are operating below the breakdown voltage, can be used as an insulator to see.

However, in AC circuits, because the direction of the current over time as a function of certain changes. The process of charging and discharging the capacitor is a time, and this time, the changing electric field between the plates is formed, and this is also a time-varying electric field is a function. In fact, the current is in the form of an electric field between the capacitor through.

At the secondary level, there is a saying, called through exchanges, DC blocking, that is the capacitance of this nature.

Capacitance effects:

1) Bypass

Bypass capacitors provide energy storage devices for local devices, which enables the regulator output uniformity, reduce the load demand. Like small rechargeable batteries, bypass capacitors can be charged to the discharge device. To minimize impedance bypass capacitors as close as possible load device power supply pins and ground pins. This can well be prevented ground elevation and excessive noise input values caused. Ground is connected to the voltage drop at the time by the large current spikes.

2) Decoupling

Decoupling, also known as decoupling. From the circuit, it can always be divided into the driving source and the driven load. If the load capacitance is large, the driving circuit charging the capacitor should discharge to complete the transition signal, the rising edge relatively steep when the current is relatively large, so that the drive current will absorb a large supply current in the circuit inductance, resistance (especially on the pin inductance chip) will have to rebound, this current is relative to the normal situation, it is actually a noise, it will affect the normal operation of the preceding stage, which is called "coupling."

Decoupling capacitors is to play a "battery" role, to meet the current drive circuit changes, to avoid mutual interference coupling in the circuit to further reduce the impedance of the power frequency interference between the reference ground.

The bypass capacitors and decoupling capacitors combine more readily understood. The actual bypass capacitor is decoupled, but generally refers to bypass high frequency bypass capacitor, which is provided to the high frequency switching noise in a low impedance discharge pathway. High frequency bypass capacitors are generally relatively small, according to the resonant frequency is generally taken 0.1μF, 0.01μF etc; away coupling capacitance for generally higher, may be 10μF or greater, based on distributed parameter circuit, as well as changes in the size of the drive current determined. Bypass is the input signal as filtered interference objects, the decoupling is to filter out the interference of the output signal as an object, to prevent the interference signal power return. This should be the essential difference between them.

3) filter

In theory (which assumes a pure capacitance capacitors) that the larger capacitance, impedance is smaller, the higher frequency through. But in fact more than 1μF capacitor mostly electrolytic capacitors, inductors have great ingredients, so instead of the high frequency impedance will increase after. Sometimes see a larger capacitance electrolytic capacitor in parallel with a small capacitor, then a large capacitor filter low frequency, high frequency small capacitor filter. Capacitance effect is through the exchange of DC blocking, pass the high-frequency low-resistance. More easily by the high-frequency capacitance increases. Specifically for use in filtering, large capacitor (1000μF) filter low-frequency, low capacitance (20pF) filter frequencies. Users had the image of the filter capacitor as a "pond." Because the voltage across the capacitor is not mutated, can be seen, the higher the frequency the greater the attenuation can be the very image of said capacitor like a pond, not by the addition of a few drops of water or evaporation of water caused by the change. It is converted to variable voltage change in the current, the higher the frequency, the greater the peak current, thereby buffering the voltage. Filtering is charging and discharging process.

4) storage

Energy storage capacitor through a rectifier charges collected, stored and transmitted by the transducer leads to the power supply output. Voltage rating of 40 ~ 450VDC, capacitance values between 220 ~ 150 000μF electrolytic capacitors is more commonly used. Depending on the power requirements of the device sometimes used in series, parallel or a combination thereof, for the power level than 10KW power, usually a larger volume of the tank-shaped screw terminal capacitors.

Please wait Capacitor 3. ^_^






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