Electronics > Beginners

SMPS chip but not for 240V?

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mikeselectricstuff:

--- Quote from: FriedMule on September 04, 2019, 06:53:00 am --- But In my book it looks like that 240V is connected to the chip?

--- End quote ---
That is rare - the most common arrangement is a resistive dropper from HV to get it started, then use a winding on the transformer for normal running. 

There are some pure buck converters designed for mains voltages, look at Power Integrations' LinkSwitch series.
The reason that simple buck converters aren't common for mains is that mains PSUs usually need isolation, so a flyback with a transformer makes the most sense.

tunk:
I guess it's a bit beside the point, but the 240V is an average and
after rectification and smoothing it's more like 340V (240*2^0.5).

You could also take a look at some of DiodeGoneWild's youtube videos.

FriedMule:
Oh, that makes a  lot of sense. What are the difference between the two schematics? Safety, efficiency, pros / cons?

FriedMule:
Bump:
I am not asking for a scientific explanation, just a simple one, since one has a lot more components then the other but both should buck converters. :-)

james_s:
Buck converters do not provide isolation between line and load. Typically if you are going to go to the effort of making a off-line SMPS you may as well go with an isolated topology.

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