The Function of Capacitors

1) Bypass

Bypass capacitors is storage device which provide the energy for the local device. It can make the output of stabilizer homogenization, reduce the load demand.  Just like small rechargeable battery, bypass capacitors can be charged, and discharge electric to the device. To minimize impedance, bypass capacitors try to close to the power supply base pin of the load device. This is able to prevent the raise of around potential and noise caused by the too large input value.

2) Decoupling

From the aspect of the circuit, it is always can be divided into the drive source and the driven load. If load capacitance is bigger, drive circuit recharge and discharge the capacitance to complete the saltus step of the signal. when the signal is rising along the steep, current is bigger, so drive current can absorb a lot of the source current, because stray inductance, resistance, relative to the current normally condition, it is actually a kind of noise, it will affect the normal work of the former stage, this is the so-called “coupling”.

Bypass is to treat the interference of the input signal as filter object, but decoupling is to put the output signal interference as filter object, prevent interference signals to return to power. This should be the essential difference between them.

3) Filter

In theory (i.e. hypothesis capacitance for pure capacitance), the bigger the capacitance, the smaller the impedance, the higher the frequency through. But in fact more than 1 µ F capacitance mostly is the electrolytic capacitor which has the greater inductance ingredients, so after the high frequency it will increase the impedance. Sometimes we see there is a big electric capacity electrolytic parallel a small capacitor, at this moment the big capacitance passes low frequency, small capacitance passes the high frequency. The role of the capacitor is to pass the high frequency resist low frequency. In the specific use of filter, the great capacitance (1000 µ F) filters the low frequency; small capacitance (20 pF) filters high frequency. Filter is the process of charging and discharging.

4) Energy storage

Energy storage type capacitor collects the charge through the rectifier, and sent the storage of energy through the converter to the power supply output terminal. Electrolytic capacitors, with the voltage rating in 40 to 450 VDC, capacitance in 220 ~ 150 000 µ F, is relatively commonly used. According to the different requirements of power supply, the device will sometimes have series, parallel, and series-parallel or their combination of the form, for power levels of more than 10 KW power source, it usually adopts large tank form spiral terminal capacitors.