On Tuesday, Mar 16, 2004, at 15:32 US/Pacific, Byron A Jeff wrote:

> I think you missed my point. The 78LXX parts are fine for some
> applications.  However linear regulators will burn through any power
> budgeted applications like a battery based one.

Nonsense.  As long as your actual application is low current, you CAN
design a linear regulator that is also low current.  It won't
necessarily be very efficient, but it can do much better than a 78L05.
The problem with the 78L is not so much the inherent inefficiency of
linear regulation, but the relatively high "idle" current (5mA, someone
said?), which is MUCH larger than a PIC in idle mode, for instance.
You can run for a long time using a linear regulator if the whole thing
draws an average of 0.5mA, even if the efficiency is relatively poor.
A simple zener regulator is probably a good example; given reasonably
accurate ideas of minimum and maximum current consumption of the
circuit, you can design a zener circuit that is "maximally efficient
for a linear regulator."

Don't forget that switchers frequently have restrictions on minimum
current supplied.  While they're great (relatively speaking) for
getting maximum EFFICIENCY for a relatively high-current application,
they are NOT always the best solution for a low-current device.  (Of
course, there are nice chips specifically aimed at high "stand-by"
times in devices like PDAs and Cell phones that ARE optimized for some
low-current delivery.  Interestingly enough, sometimes these include
linear portions for some of their outputs...)

BillW

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