Winfield Hill wrote...

Perhaps my circuit can be combined with Jim's circuit:

: +6.0V, from wall wart
: --+------+------+
: | | |
: | 220 | Q1 2sa1011
: | | |/E pnp TIP32
: 750 +----| etc
: | | |\
: | |/ |
: +----| Q2 |
: | |\E npn |
: | | |
: | +---+--+---- + output
| | to load
__|___/ 2.7k
/ /\ |
/ \--------o
/ \ |
-------- 2.7k
| TL431 |
| |
- ----o----------o------- -

I'm still not happy with the poor dropout-voltage capability of
this circuit. It should be able to operate with Vin much closer
to Vout. Aha! Simply adding a diode and resistor lets us reduce
the dropout voltage down to near the saturation voltage of Q1.

: +5.3 to 9V
: --+-----+------, SIMPLE 5.0V REGULATOR
: | | |
: | 220 | Q1 2sa1011
: | | |/E pnp TIP32
: 470 o----| etc
: | | |\
: | |/ |
: o---| Q2 '----o---- +5.0V
: | |\E npn | output
: | | | to load
: | | 1n4148 |
: | '--o--||---o
| | |
__|___/ 1k 2.7k
/ /\ | |
/ \----- | -------o
/ \ | |
-------- | 2.7k
| TL431 | |
| | |
- ----o--------o--------o---- -

Of course, an even more simple circuit is possible, using one
of the many low-cost low-dropout three-terminal regulator ICs.

: +5.3 to 9V etc
: -------, EVEN MORE SIMPLE 5.0V REGULATOR
: __|__
: | |
: | |---+--- +5.0V
: |_____| _|_ output
: | --- to load
: | |
: - -------o------o--- -

But this circuit isn't as much fun. :)

Thanks,
- Win

whill_at_picovolt-dot-com