As one of the most widely used electronic components, capacitor has many functions. Filtering is one of the most common functions of capacitors. What is a filter capacitor? What is the role of the filter capacitor?
Capacitance is two conductors that are close to each other and insulated from each other.
Filter capacitor is an energy storage device installed at both ends of the rectifier circuit to reduce the RIPPLE coefficient of AC pulsation and improve the efficient and smooth DC output. Because the filter circuit requires the storage capacitor to have a large capacity. Therefore, most filter circuits use electrolytic capacitors. Electrolytic capacitors get their name from their use of electrolytes as electrodes (negative electrodes).
A capacitor (or bank of capacitors) connected with other accessories, such as reactors and resistors, to provide a low impedance channel for one or more harmonics. It has the characteristics of small size, light weight, easy to carry, little leakage current and so on.
The role of filter capacitor: the role of electrolytic capacitor is to filter out the low frequency signal in the current, but even the low frequency signal, its frequency is divided into several orders of magnitude. Therefore, in order to be suitable for use at different frequencies, electrolytic capacitors are also divided into high frequency capacitors and low frequency capacitors (here the high frequency is relative).
The low-frequency filter capacitor is mainly used for filtering after electrical filtering or transformer rectification. Its working frequency is 50Hz, which is consistent with that of the mains. And the high frequency filter capacitor mainly works in the switching power supply rectification after filtering, its working frequency is thousands of Hz to tens of thousands of Hz. When low frequency filter capacitor is used in high frequency circuit, due to its poor high frequency characteristics, its internal resistance and equivalent inductance are high when charging and discharging at high frequency. Therefore, in use, the electrolyte will produce large heat due to frequent polarization. The higher temperature will vaporize the electrolyte inside the capacitor, increase the pressure inside the capacitor, and eventually lead to the bulge and burst of the capacitor.
The role of filter capacitor is mainly used in the power supply rectifier circuit to filter out ac components. Make the dc of the output smoother. And for precision circuits, the combination of shunt capacitor circuits is often used to improve the working effect of filter capacitor.
The role of the filter capacitor is to produce different operating frequencies according to the difference between low and high frequencies:
The low-frequency filter capacitor is mainly used for the filtering of mains or transformer rectification, and its working frequency is 50Hz as that of mains; The high frequency filter capacitor mainly works in the filtering after switching power supply rectification, and its working frequency is from thousands of Hz to tens of thousands of Hz.
Filter capacitor plays a very important role in switching power supply, how to correctly select filter capacitor, especially the selection of output filter capacitor is very concerned by every engineer and technician.
Common electrolytic capacitors used in 50 Hz power frequency circuits have pulsating voltage frequencies of only 100 Hz and charge and discharge times of the order of milliseconds.
In order to obtain a smaller ripple coefficient, the capacitance required is up to hundreds of thousands of micromethods, so the goal of ordinary low-frequency aluminum electrolytic capacitors is mainly to improve the capacitance, capacitor capacitance, loss Angle tangent value and leakage current are the main parameters to identify its advantages and disadvantages.
The output filter electrolytic capacitors in switching power supply have sawtooth wave voltage frequencies up to tens of thousands of Hertz, or even tens of megahertz.
At this time, capacitance is not the main index, and the standard to measure the advantages and disadvantages of high frequency aluminum electrolytic capacitor is "impedance frequency" characteristic. It is required to have a low equivalent impedance in the operating frequency of the switching power supply and have a good filtering effect on the high frequency peak signal produced by the semiconductor device.
Ordinary low-frequency electrolytic capacitors begin to show sensibility at about ten thousand Hertz, which cannot meet the requirements of switching power supply.
The high-frequency aluminum electrolytic capacitor for switching power supply has four terminals. The two ends of the positive aluminum sheet are respectively led out as the positive electrode of the capacitor, and the two ends of the negative aluminum sheet are respectively led out as the negative electrode. The current enters from one positive end of the four-terminal capacitor, passes through the capacitor, and then flows to the load from the other positive end; The current returned from the load also flows through one negative end of the capacitor and from the other negative end to the negative end of the power supply.
The role of the filter capacitor as the name suggests is obviously primarily for filtering.
