On Wed, Dec 15, 2010 at 12:32 AM, John Gardner <goflo3@gmail.com> wrote:

> When all else fails, do it right :)
>
> What's the beef with switchers?
>

Couldn't have said it better myself.

As for the beef with switchers, there's generally a higher part count
associated with them. That's all. And it was hard to find one with the righ=
t
specifications.

Even the TI one has a maximum input voltage of 5.5 volts. Now i'll need a
CMOS comparator and a couple of power FETs to route current through a high
power schottky/germanium diode with about a 0.3 forward volt drop if the
battery voltage is greater than 5.5 volts. I don't think the battery pack
will go above 5.8 volts at any point.

I have no idea where to get a 5.5 volt voltage reference though. An LDO
sounds good, but then it'll drop out before it reaches 5.5 volts.

I'm thinking another solution would be to use a 5 volt LDO (low power),
compare the 5 volts from there with the voltage from the raw battery pack
through a resistor divider. I'd arrange the divider's output to be 5 volts
when the battery pack voltage is 5.5 volts. Any higher, and the divider
output would be greater than 5 volts and power would be routed through a
power diode. Any less than 5.5 volts and the divider output would be less
than 5 volts and the comparator would route current directly to the
switching supply.

I already am sampling the switching supply and some comparators from TI.
--=20
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