I have a project to designe a power supply with this specifications:

input 220v ac
output: 24,12,9 or 5 dc volt
range (1.2 - 2)
I also need to understand the meaing of range here.
I must use step-down transformer, compartor (with reverence volt) , Transistor.

I'll be gratefull, if I get a help, Thank you......

 

You need to know the current for each output and the tolerance of each (like 3%, 2%, etc).

 

Reverence voltage - I like it.