I asked a question here which made it quite clear that it's probably not a good start to make something that I plug directly into the mains.
Instead, I've decided to build a low-voltage buck converter for starters. But I've run into something I don't understand.
1) You need a stable voltage to power your switching IC, or external circuit, or what have you. Usually lower voltage than the current you're trying to lower. 2) You need a stable reference voltage for your switching mechanism so it knows when it's duty-cycle is right on.
With these two things required in a buck converter, it seems you've already accomplished your end just to build the buck converter. I.E. you have to have pre-established stable, lower voltages to run a buck converter who's purpose is to produce a stable, lower voltage.
Why would you want a buck converter, and how does one establish a reference voltage and a voltage to power the switching mechanism?
Reading both the answers I think I understand. For the switching mechanism, we KNOW the load it's going to draw and can plan accordingly. We can produce a very stable linear regulator if we know how much the load will be. We can even account for little fluctuations with a zener diode.
However, using the same process for the overall power supply would be inefficient, and if we drew too much current, the heat emanating from the components would be uneconomical. this is without mentioning that we would be unable to switch the load without getting a different voltage.