With the advent of modern ICs and circuits, the age old iron transformer type of power supply are surely becoming obsolete. Today power supplies are much compact, smaller and efficient with their functioning. Here we discuss one outstanding switch mode power supply circuit which can be easily built at home for deriving clean, ripple free 12 V DC. ST Microelectronics IC, the VIPer22A, which has made the construction of truly efficient and compact SMPS power supply unit possible that too by using a very few number of electronic parts. As can be seen in the picture, the circuit is indeed very small, compared to the power that is available from it. It's just 50 by 40 mm in its dimensions. The circuit diagram is very easy to understand, let's study it with the following points: Looking at the figure we can easily see that the configuration does not involve too many stages or parts. The input mains AC, as usual is first rectified using ordinary 1N4007 diodes which is fixed in the bridge network mode. The rectified high voltage DC is filtered using the high voltage capacitor. The next stage is the crucial one which incorporates the outstanding chip VIPer 22A manufactured by ST Microelectronics. The IC alone functions as the oscillator and induces a frequency of around 100 KHz into the primary winding of the ferrite E core transformer. The IC is absolutely rugged and is internally protected from sudden voltage in rush and other voltage related component hazards. The IC also incorporates built in over heat protection which makes the IC virtually indestructible. The voltage induced at the input is effectively stepped down at the output winding, due to low eddy current losses, about 1 amp current becomes available from a relatively tiny ferrite transformer. With the coil specs shown the voltage is around 12 and the current is around 1amp. A special feedback circuitry is also included in the circuit for maintaining high degree of protection and power saving features. The feedback loop is implemented via an opto-coupler which becomes active during abnormal circuit conditions. When the output voltage tends to rise beyond the set threshold the feed back loop becomes operative and feeds an error signal to the IC FB input. The IC instantly comes into an corrective mode and switches off the input to the primary winding until the output returns to the normal range.