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What is the filter capacitance? What is the function of the filter capacitance?

date: 2019-08-28
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When we were students studying physics, we always saw a term in the circuit chapter: capacitor.As one of the widely used electronic components, capacitor has many functions.Filtering is one of the most common functions of capacitors.Do you know what a filter capacitor is?And what is the function of the filter capacitor?Today, we're going to take a look at what a filter capacitor is and what a filter capacitor does.


What is filter capacitance?


Filter capacitor: it refers to 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.Since the filter circuit requires large capacitance of energy storage capacitor.Therefore, most filter circuits use electrolytic capacitors.Electrolytic capacitors are named for their use of electrolytes as electrodes (negative electrodes).


What is the function of the filter capacitor?


The function of filter capacitor is mainly used in power supply rectifier circuit, used to filter out ac components.Make the dc output smoother.And for precision circuits, the combination of parallel capacitor circuits is often used to improve the performance of filter capacitor.


The effect of filter capacitor produces different working frequency according to the difference of low frequency and high frequency:


The low-frequency filter capacitor is mainly used for the filter of mains power or the filter after transformer rectification, and its working frequency is consistent with mains power at 50Hz.The high-frequency filter capacitor mainly works in the filter after the switching power supply is rectified, and its working frequency ranges from several thousand Hz to tens of thousands of Hz.


Filter capacitor plays a very important role in switching power supply. How to choose filter capacitor correctly, especially the choice of output filter capacitor, is a very important problem for every engineer and technician.


A typical electrolytic capacitor used in a 50 hz power frequency circuit has a pulsating voltage frequency of only 100 hz and a charging and discharging time of milliseconds.


In order to obtain a smaller pulsation coefficient, the capacitance required is up to hundreds of thousands of micromethods. Therefore, the main goal of ordinary low-frequency aluminum electrolytic capacitors is to improve the capacitance, and the capacitance, tangent value of loss Angle and leakage current are the main parameters to identify their advantages and disadvantages.


And the output filter electrolytic capacitor in the switching power supply, its sawtooth wave voltage frequency is up to tens of Hertz, or even tens of megahertz.


At this time, capacitance is not the main index, the standard to measure the merits of high frequency aluminum electrolytic capacitor is 'impedance - frequency' characteristic.It is required to have a low equivalent impedance within the operating frequency of the switching power supply and to have a good filtering effect on the high frequency peak signal generated by the semiconductor devices.


Ordinary low frequency electrolytic capacitors begin to show sensibility around 10 kilohertz, which cannot meet the requirements of switching power supply.


The special high-frequency aluminum electrolytic capacitor for switching power supply has four terminals. The two ends of the positive aluminum sheet are respectively drawn out as the positive pole of the capacitor, and the two ends of the negative aluminum sheet are also drawn out as the negative pole.The current flows from one positive end of the four-terminal capacitor, through the inside of the capacitor, and flows from the other positive end to the load;The current returned from the load also flows from one negative end of the capacitor to the other negative end of the supply.


The function of the filter capacitor, as the name suggests, is clearly primarily for filtering.


This is the function of filter capacitor in detail, do you have more understanding of the function of filter capacitor?If you want to know more about what a filter capacitor is and what it does, please follow us.


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