trying to design a power supply when you don't know how much current you're going to need, and when you're concerned about efficiency, and you absolutely have to make it linear (noise would mess up research stuff)... fun times
what we know: we need at least 750mA (call it an amp for headroom) at 15V
this is not hard, get a 14V or 16V AC source (transformer) and rectify etc.
but we have reason to believe we may also need a nontrivial amount of current at 5V, and I don't exactly want to be dropping 15V to 5V at like 2A in a linear regulator, so do they make transformers for 14VAC to 5VAC at 10-ish watts, or something like that?
we don't know enough about magnetics to be comfortable winding our own transformer if it's going to be carrying a nontrivial amount of power
tempted to just say fuck it and stick lead-acid batteries in there all over the place. oof
not going to but it should not be this hard to build a power supply using technology that's been around for like six decades
okay we're overdesigning this
just gonna, stick a 7815 in there for the 15V thing, use a schottky bridge rectifier and a big cap, and we'll worry about anything on lower voltages when those things actually get designed in
or some other linear regulator, maybe we can use an LDO and a capacitor that's less than 20mF
I don't _really_ want to be using a 16VAC input to this, 14VAC is sufficient and it's already gonna be dissipating a lot of power