The first inductor lying in the SMPS

What or how exactly is the first inductor's function and working mechanism lying in most SMPS as shown?



Thanks much in advance.

RFI filter, both ways - along with all the associated capacitors. In countries with good quality mains they often aren't fitted, or at least some of them aren't, with wire links replacing any series components passing current. It's common to see PCB's with loads of parts not fitted on the mains inputs, often there's space for a second filter as well.

Nigel Goodwin said:

RFI filter, both ways - along with all the associated capacitors. In countries with good quality mains they often aren't fitted, or at least some of them aren't, with wire links replacing any series components passing current. It's common to see PCB's with loads of parts not fitted on the mains inputs, often there's space for a second filter as well.

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You get good quality mains only when they are fitted!!!. Else the mains supply will be loaded with spurious emissions.

Ramussons said:

You get good quality mains only when they are fitted!!!. Else the mains supply will be loaded with spurious emissions.

Click to expand...

It depends partially which way you're wanting to stop interference, very often in the UK with our high quality mains very few of the filter components are fitted, whereas the exact same devices in Spain (I've repaired quite a few devices sent back from Spain) have all the filter components fitted, and still commonly get blown up by mains issues.

This is why it's not a good idea to buy electronics in the UK and take it out to Spain

Biggest issue is probably failing (sub-standard) capacitors in SM wallwarts, these commonly fail and send lot's of interference back out the mains - often causing substantial issues for ADSL.