The very famous architecture is the TL494 IC and PC AT/ATX power supplies. There are tons of related files on the internet, just "google", download, and studying. Easy to practise with any PC power supply units.
mean if we apply 220 to the step down transformer and o/p is 12v ac and the it fed to the ac to dc covertor controller whose rectifcation can be controlled
build the full wave bridge rectifier....You only need four diodes for the circuit....If you will to have a better shape on the output (less ripple), you need to place a capacitor in parallel to the load...