Hi.. I need to design a switching power supply with 220 V AC (50 Hz) input and 12 V DC 3A output. The design must not use a transformer (need to be embedded in small 2.5'' by 2.5'' assembly). I will be thankful if along schematic solutions, some one may contribute with reading material regarding switching supply designs.
Thanks.
If you design a psu like that then you need to be careful and design a safe circuit because this is a high voltage design.
I also find difficult the part of building/finding the appropriate inductor/transformer.
My suggestion would be to buy a ready 12V pulse psu which are available for computers and especially since you want a very common output voltage.
You can find ready psu like the one in the picture (12v/5A) in prices starting from $8 including shipping in ebay (from HK sellers)