Some people will say it only makes sense to use a dc-dc converter, since standard
v.regs tend to waste power. But I'll only mention some v.reg considerations.
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most people use a 1-AMP v.reg, so try to go with that.
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you want a low-dropout [LDO] v.reg, so the usual 7805 and LM317 are not good
choices. For TO-220, the LM2940 is a good choice. Most or a lot of smt v.regs are
LDO. -
in regards packaging, I personally dislike the tiny SOT223 v.regs found on many
boards. After LDO, the next most important aspect is Pd = power dissipation.
The little SOT223 v.regs will overheat when dissipating more than 0.3W or so,
and that's not much of a load, after all. For a 9V power source,
Iload = 0.3W/(9V-5V) = only 75mA. That's really a tiny load current.
I prefer using a TO-220 for the main v.reg, since it can dissipate a lot more power
without overheating. Or at least a DPAK, which is inbetween TO-220 and SOT223.
- in regards having both 5V and 3.3V v.regs, I was EXTREMELY disappointed with my
Duemilanove board when I discovered the 3.3V power went away when I disconnected
from USB and ran off a battery. Nuf said.