hii
i've got a minor project to build a power supply with the rating
0-15 var;
0.5amp
10%reg
i've got the basic idea but i'm unable to calculate perfectly the values of the capacitors (as filters) and transistors for regulation.
The analogue PS chips uses an OPA as error voltage detection (difference between output and reference voltage). Therefore the minimum output depends on the OPA’s drift voltage. For analogue chips (LM317, uA723…) is typical 1,2…1,7V. If is very important to adjust down to 0V, you must use a double DC supply (transformer with centred tap), or a switching PS (ex.: 78s40).
Download the chip’s datasheets, because they usually contains a simple applications.
I agree a rather large center tap transformer is needed to split the voltage and step it down as well.
Since this is a high voltage, ganging two 120 volt rated transformers might be impractical.
This all depends on how complex you want to go and what it is going to drive, as the complexity ranges greatly form a full rectified filtered regulated PS to a complex switcher PS.
I would say since your trying to push 1 amp a single step down trans with a rectifier filter network and a regulator or transient voltage suppressor zener would work fine.