SMPS chip but not for 240V?

[FriedMule]

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.

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 
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 

I am glad for your warning, but the mains side of the project am I not unsure about, it is the part I know most about and have done most work on, i.e. at worksites and home, I am not an electrician but can do most installations. I am also planning on using a variac for a minimum of safety.
I keep reading, look at videos and know that there is a lot to learn. All I have previously done is bould "old" school power supplies.

Do you have any advices, beside YouTuber DiodeGoneWild on who to wach, where to read and so on?

[james_s]

You are in way over your head, I don't intend to sound rude however if you had the knowledge to do this safely and successfully you would not be asking many of these questions. SMPS design is a rather advanced topic and you will need to be proficient at all the underlying concepts. If you don't get everything just right, they have a tendency to blow up instantly when power is applied, or if they work they may be spewing copious amounts of RF hash and knocking out radio or TV reception. You are asking someone to explain to you how to fly a 787 when you have never flown a Cessna or drive a Ferrari when you have never driven a basic passenger car.

Start reading every application note and textbook you can find on the subject, study existing designs, eventually you will get there but it's not easy.

[soldar]

You are in way over your head, I don't intend to sound rude however if you had the knowledge to do this safely and successfully you would not be asking many of these questions. SMPS design is a rather advanced topic and you will need to be proficient at all the underlying concepts.

+1

I have repaired dozens of this type of SMPS and have a pretty good understanding but I would not dream of building one. I would still need to study and learn a lot more. A lot. This is a very specialized field and no one is going to be designing and building this in a few hours.

[FriedMule]

You are in way over your head, I don't intend to sound rude however if you had the knowledge to do this safely and successfully you would not be asking many of these questions. SMPS design is a rather advanced topic and you will need to be proficient at all the underlying concepts.

+1

I have repaired dozens of this type of SMPS and have a pretty good understanding but I would not dream of building one. I would still need to study and learn a lot more. A lot. This is a very specialized field and no one is going to be designing and building this in a few hours.

You are in way over your head, I don't intend to sound rude however if you had the knowledge to do this safely and successfully you would not be asking many of these questions. SMPS design is a rather advanced topic and you will need to be proficient at all the underlying concepts. If you don't get everything just right, they have a tendency to blow up instantly when power is applied, or if they work they may be spewing copious amounts of RF hash and knocking out radio or TV reception. You are asking someone to explain to you how to fly a 787 when you have never flown a Cessna or drive a Ferrari when you have never driven a basic passenger car.

Start reading every application note and textbook you can find on the subject, study existing designs, eventually you will get there but it's not easy.

Sorry that I was not clear. What I meant was that the safety and handling mains, is what I know most about. I can understand that you could compare me to knowing the sea and how to navigate it safe, but what I am trying to do is to sail around the world in a DIY atomic u-boad:-)
My error in thinking that I could build a SMPS was that Dave, in a video is saying that it is almost the same, that the one is not much harder then the other. And since I know how to make a decent linear power supply, what was then holding me back? :-)

[soldar]

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

They are basically the same thing. One is a conceptual explanation of how the circuit works and the other is an actual application. The first one omits many minor things not needed to understand the working of the circuit.

You need to read, study and understand the document in its entirety. You are asking questions which are answered in there. Reading manufacturers' application notes is a very good way of learning.

You need to read up about the different topologies and what they are good for. Nobody can give you here the basic knowledge needed to design SMPS. That requires hundreds of hours of study and learning.

For a start:
http://ww1.microchip.com/downloads/en/appnotes/01114a.pdf

BTW, it says

A  buck  converter,  as  its  name  implies,  can  only produce  lower  average  output  voltage  than  the  input voltage.

"As the name implies"? What is the meaning of "buck" in this context? And why does it imply it con only produce lower voltage?

Another: https://www.ti.com/seclit/ug/slyu036/slyu036.pdf

[FriedMule]

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

They are basically the same thing. One is a conceptual explanation of how the circuit works and the other is an actual application. The first one omits many minor things not needed to understand the working of the circuit.

You need to read, study and understand the document in its entirety. You are asking questions which are answered in there. Reading manufacturers' application notes is a very good way of learning.

You need to read up about the different topologies and what they are good for. Nobody can give you here the basic knowledge needed to design SMPS. That requires hundreds of hours of study and learning.

For a start:
http://ww1.microchip.com/downloads/en/appnotes/01114a.pdf

BTW, it says

A  buck  converter,  as  its  name  implies,  can  only produce  lower  average  output  voltage  than  the  input voltage.

"As the name implies"? What is the meaning of "buck" in this context? And why does it imply it con only produce lower voltage?

Another: https://www.ti.com/seclit/ug/slyu036/slyu036.pdf

Thank you a lot, great links and helpful comment, I will do as you and other suggests. :-) I can also start by learning ad trying out low voltage bucks (12V to 5V) and so on, if I destroys some components on the way, no harm:-)