Alan B. Pearce wrote:
> Well I guess it would be advisable to drive all those LEDs of the 5V5
> supply, rather than the smoothed 5v or 3v3 if it gets dropped to that.

Yeah, good point.

> However to take it back a step, I do wonder just what the purpose of
> having the linear regulator is. If one is looking for real smooth
> supplies for analogue purposes then I would suggest that one would
> regulate this separately anyway to keep the supply noise from the PIC
> out of the picture.

But what would you regulate it from?  If the switcher produces 5V directly,
then there is no convenient input to a LDO to make the analog supply.  I've
found that the 5V supply stays quite clean with decent bypass caps on the
PIC and an output cap at the LDO.

> I cannot see any real advantage in not having the
> switcher give the 5V direct.

I seriously considered that, but then you are left with no easy way to get a
clean supply.  I've found that the MCP1700 with a good output cap and a
properly bypassed PIC make a quite clean supply that will be good enough for
the vast majority of 10 bit analog applications.  It's all a tradeoff, but
in the end I thought the $.35 or so for the LDO was a relatively cheap way
to cover most of the main stream applications.  The unusual applications can
jumper out the LDO and adjust the switcher feedback resistors to make any
custom voltage they want.  They will "waste" a $.35 part, but I think that
will be a small minority of applications.


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