Selection of filter Capacitor

After the rectifier bridge is pulsating DC, the fluctuation range is very large. The output is usually stabilized by two capacitors of large or small size. It is well known that the voltage at both ends of the capacitor cannot change, so that the output can be smooth and small capacitors can be used to filter out high frequency interference, so that the purer the output voltage is, the smaller the output voltage is. The higher the resonant frequency, the higher the filtered interference frequency.

Capacity selection:

1) large capacitance, the heavier the load, the stronger the ability to absorb current, the larger the capacity of this large capacitance is.

2) small capacitance, usually 104, depending on experience.

2.The experience of others (from the Internet).

1. The capacitance to ground filter needs a small capacitance parallel to the ground, which provides a ground to ground path for the high frequency signal.

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

3. Theoretically, the bigger the capacitance is, the better, the larger the capacitor is, the better, the higher the low frequency wave is, the lower the capacitance is.

4. The reliable method is to parallel a large capacitance and two capacitors, and generally require a difference of more than two orders of magnitude in order to obtain a larger filter band.

Specific case: AC220-9V after the full bridge rectifier, the need to add the filter capacitance is how big? How big is the capacitance to be added after passing through 78LM05?

The former capacitance should be more than 15V, capacitance capacity should be more than 2000 microtransmitters. The latter capacitance should be more than 9 V, capacity should be more than 220 microtransmitter.