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The selection principle of filter capacitance (I)

Views:0     Author:Site Editor     Publish Time: 2018-05-14      Origin:Site

1. After the rectifier bridge is pulsating DC, the fluctuation range is very large. Two capacitors are used in the rear, and large capacitors are used to stabilize the output. It is known that the voltage at both ends of the capacitor can not be abrupt, so the output can be smooth. The small capacitance is used to filter the high frequency interference and make the output voltage pure; the smaller the capacitance is, the higher the resonant frequency, the higher the interference frequency of the filter can be filtered.


Capacity selection:

(1)The larger the capacitance, the heavier the load, the stronger the ability to absorb the current, the larger the capacity of the larger capacitor.

(2) Small capacitance, by experience, general 104


2. People's experience (from the Internet)

1) Capacitance to ground filtering requires a smaller capacitor to parallel to the ground, providing a ground to ground access to the high frequency signal.

2) In the power filter, the capacitance should be as close as possible to the ground.

3). In theory, the larger the capacitance, the better the general capacitance.

4) Reliable method is to connect one large, one small, two capacitors in parallel, and generally require a difference of two orders of magnitude, in order to obtain a larger filtering frequency band.


Specific cases:

How large is the filter capacitor to be added to AC220-9V after full bridge rectification? How big is the capacitance that you need to add after 78LM05? The capacitance of the former should be more than 15V, and the capacitance should be more than 2000. The capacitance of the latter should be more than 9V, and the capacity should be above 220.


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