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

[blacet at blacet.com]

You can always use a series low value resistor to drop the 15V a bit and
take some of the heat before the regulator. It depends on how much current
you need and this will effect resistor value/wattage and regulator type/
heatsink requirements.


> 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?
>
> Thanks,
> Tom
>
>
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