Explain of capacitor - inductor setup

Other Hardware General Electronics
1

Hi all,

I am deigning a small power metering device that would measure power consumption in house appliances and connect via WiFi (esp8266) to Home Assistant.
The project is based on the BL2525 power measurement chip and it also involves a transformerless supply of 3.3V from mains (yes, I know its dangerous!)

The datasheet of the
BP2525_EN.pdf (908.0 KB)
includes a recommended application setup, however while searching the net for similar applications I come across the following configuration with two capacitors and an inductor after the rectification stage:

BL2525_supply

This setup appears to be used a lot in similar designs.
Can anyone explain the purpose of this block?

2

Link?

and a bigger clearer image?

First guess - its "smoothing" - like thhis

3

First guess - its "smoothing" - like thhis

Smoothing of mains ?

Sorry couldn't find a better image.
Image taken from a forum here : https://www.elektroda.com/rtvforum/topic3977697.html

4

The inductor and capacitors will filter out high freq. noise from AC.
High freq noise is present from motors with brushes (drilling machines) but also from switching power supplies. And from solar feed and so on...
Some communication systems delibrately put high freq signals on mains as means of 'wireless' communication.
Also the 0.6V over the diodes will cause high freq noise...

5

Thanks for the info!
Any idea of what the inductor value should be?

6

It is named a choke coil. It is usually not an 'ideal' inductor. It is often wrapped around a ferrite like bead.
No idea about standard specs...

7

The capacitors and inductor are to keep noise generated by the BP2525 from entering onto the AC mains line, NOT the other way around.
You may need those components in order to pass EMC testing.
For a hobby project, may not be needed

2 Likes
8

That makes sense...

9

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