Electronics > Beginners

SMPS chip but not for 240V?

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FriedMule:

--- Quote from: james_s on September 04, 2019, 06:24:51 pm ---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.

--- End quote ---
Great advice, Both of these do look like isolated, but are one better the the other?

David Hess:

--- Quote from: james_s on September 04, 2019, 03:57:08 am ---While high voltage buck converters do exist, that topology is not particularly common for such applications.
--- End quote ---


--- Quote from: oPossum on September 04, 2019, 05:42:44 am ---Typically flyback or forward converter.
--- End quote ---

The reason for this, beyond galvanic isolation from input to output, is that the transformer adjusts the ratio of voltage to current in the power switch to a more advantageous value.  If a buck converter is used, then the power switch has to handle the maximum output current and the maximum input voltage making it significantly more expensive and lowering efficiency as well.  The transformer in a flyback or forward converter considerably reduces the current which the power switch must handle.

FriedMule:

--- Quote from: David Hess on September 04, 2019, 10:33:09 pm ---
--- Quote from: james_s on September 04, 2019, 03:57:08 am ---While high voltage buck converters do exist, that topology is not particularly common for such applications.
--- End quote ---


--- Quote from: oPossum on September 04, 2019, 05:42:44 am ---Typically flyback or forward converter.
--- End quote ---

The reason for this, beyond galvanic isolation from input to output, is that the transformer adjusts the ratio of voltage to current in the power switch to a more advantageous value.  If a buck converter is used, then the power switch has to handle the maximum output current and the maximum input voltage making it significantly more expensive and lowering efficiency as well.  The transformer in a flyback or forward converter considerably reduces the current which the power switch must handle.

--- End quote ---
Yes I see the logic in that and you do also, as written earlier" get added safety". What I am out to achieve is a 240V to 5V isolated smps. Since I have about no idea on what to do, I hope that some of you could point me to a schematic that is universally okay. I know that higher frequency is better but do also demand a lot more skills in designing the circuit board.

MosherIV:
There is no one circuit that is universally ok, it depends on the parameters of the circuit.
Easiest is to find app notes for particular devices.

Building your own  :o
It is highly dangerous - there is rectified mains, HV DC, with all the power of your national grid behind it !
It is very difficult to find the isolation transformers. They are not easily available off  the shelf.

If you are doing this for learning, be very careful  :)

BravoV:
Just because you could do & probably understand "buck converter" from say 12 V down to 5 V, it doesn't mean you can still to stick with buck converter ONLY to do mains 240V AC down to 5 V DC.

Go learn and study further other topologies as pointed by many posters above, that is not smart safe method of practicing electronics, especially related to mains voltage.

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