[sdiy] Best way to get a +3.3V rail from +15V?

[Magnus Danielson]

On 03/07/2013 02:07 PM, Tom Wiltshire wrote:
> Hi all,
>
> I'm putting a little dsPIC prototype dev board together for mucking about on. I've done such things before, but I've always had a +5V supply available, so when I've needed a 3.3V rail for the dsPIC, I've stuck a regulator on the 5V supply. Which was fine, but that's not the situation this time.
>
> If I've only got +/-15V available, what's the best way to derive a 3.3V rail?
>
>
> I've used 3.3V regulators on the 15V rail before and found they got hot, which wasn't a surprise seeing how much voltage they've got to lose somewhere. But perhaps I was doing something wrong?

You should get a small switcher for a drop-switching. That way you avoid 
having to burn (15-3.3) times the current you use. For the current that 
I assume you will consume, it will be a small switcher and a handful of 
components.

Maxim and TI springs to mind, among others.

Be sure to layout it well and keep good filtering for isolation.

Cheers,
Magnus