On Sun, 05 Jun 2011 13:12:04 -0700, Jim Thompson
wrote:

On Sun, 05 Jun 2011 15:09:06 -0500, John Fields
wrote:

On Sun, 05 Jun 2011 12:20:34 -0700, Jim Thompson
wrote:


Too complex, see attachment...

...Jim Thompson

---
Something's wrong.

With a 5V supply, how can you expect to get 5V out of an emitter
follower?

The OP said his device was guaranteed at 4.2V and seemed pretty good
down to 3.7V ;-)

...Jim Thompson

---
The OP doesn't know what the **** he's talking about, and is basing
his 3.7V data on non-guaranteed characteristics of a single device
he's dicking around with.

Even with that, the data for your circuit shows that with 5V out of
the bulk supply he'll get about 2.5V into the switcher, which won't
work, for sure.

With my excellent "P" channel pass device design, , 5V out of the
supply will get him 4.95V into the switcher.

More parts than yours, for sure, but mine works down to the bitter
end.

--
JF