Dingfeng Capacitor---the Function of Capacitor
Issue Time:2016-06-08

Dingfeng Capacitor---the Function of Capacitor

As one of passive components of capacitance, the effect is the following:

1, the application in the power circuit, the realization of the bypass, decoupled, filter and energy storage.Detailed classification of the below:
1) bypass
Bypass capacitors is to provide energy for the local device of energy storage device, it can make the output of the voltage regulator homogenization, reduce the workload requirements.Like a small rechargeable battery, bypass capacitors can be charged, and discharge to the device.To minimize the impedance to bypass capacitors, try to close to the load device power supply pin and pin.It can effectively prevent the input value is too large and cause the earth potential of raises and noise.Play is ground connection at the voltage drop across the large current burr when.
2) decoupled
Go to lotus root, also called decoupled.From circuit for, always can be divided into driving source and driven load.
If the load capacitance is large, driver circuit to the capacitor charging, discharge, to complete the signal jump, rising along the relatively steep, current is larger, this will absorb a lot of drive current of the power supply current, because in the circuit inductance, resistance (especially the inductance on the chip pins, can produce a rebound), the current relative to normal, in fact is a kind of noise, affect the normal work of the level before, this is known as the "coupling".
Decoupled capacitance is play the role of a "battery", meet the changes of driving circuit current, avoid mutual coupling interference.
Combine bypass capacitors and decoupled capacitance will be easier to understand.Bypass capacitors actually also to coupling, just bypass capacitors generally refers to the high frequency bypass, also is to give the switch of high frequency noise increase a low impedance leakage prevention way.High-frequency bypass capacitors tend to be small, according to the resonant frequency is generally take 0.1 mu, 0.01 mu F F, etc.;
And the capacity of the coupling capacitance, generally larger, could be 10 u F or greater, based on the distributed parameter in the circuit, and the change of the drive current to determine the size.
Bypass is interference of the input signal as object, filtering and decoupling is the interference of output signal as the filter object, to prevent interference signal to return to power.This should be the essential difference between them.
3) filter
Theoretically (i.e. assuming capacitance of pure capacitance) said, the greater the capacitance, impedance is smaller, by the higher the frequency also.But in fact more than 1 u F capacitance mostly for electrolytic capacitors, has a large inductance component, so after high frequency impedance increases.Sometimes see a larger capacitance electrolytic capacitor in parallel with a small capacitance, then large capacitance at low frequency, small capacitance high frequency.Lao capacitance effect is low resistance, high frequency resistance at low frequency.The more easily through the low frequency, the greater the capacitance of the high frequency easier to pass.Specific use in filtering, large capacitor (1000 u F) filtering and low frequency, small capacitance (pf) 20 high frequency filter.
Have net friend vividly compared filter capacitance to "pool".Due to the inability of the ends of the capacitor voltage mutation, therefore, the higher the signal frequency, the greater the attenuation, can say very image of the capacitance is like a pool, not caused by the addition of a few drops of water or the evaporation of water.It changes the voltage changes into current, the higher the frequency, the greater the peak current, so as to buffer the voltage.Filtering is charging and discharging process.
4) storage
The energy storage capacitor through the rectifier to collect electric charge, and the energy will be stored by converter leads to the output of the power supply.Voltage rating for 40 ~ 450 VDC, capacitance between 220 ~ 150 000 mu F aluminum electrolytic capacitor (e.g., EPCOS B43504 or B43505) is relatively common.According to the requirements of the different power supply, the device is sometimes in the form of series, parallel, or their combination, for more than 10 kw power level of the power supply, usually adopt bulky cylindrical screw terminal condenser.
2, used in signal circuit, the main complete coupling, oscillation/synchronization and time constant:
1) the coupling
For example, a transistor amplifier emitter has a self-bias resistance, pressure drop it at the same time, make the signal feedback to the input form the input and output signal coupling, this resistance is produced a coupling element, if on both ends of the resistor in parallel to a capacitance, due to the appropriate capacity capacitor on the impedance of the ac signal is small, thus reducing the resistance coupling effect, therefore calls the capacitance as decoupling capacitor.
2) oscillation/synchronization
Including the load capacitance of RC, LC oscillator and crystal belong to this category.
3) time constant
This is the common integral circuit, composed of R, C series.When the input signal voltage on the input capacitance (C) the voltage rise gradually.As the voltage rises and the charging current is decreased.Electric current through a resistor (R), capacitance (C) the characteristics described by the following formula:
(I = V/R) e - (t/CR)