Steve Nosko wrote:
(snip)
FYI:
On one I built, I wound a few extra turns on the transformer and added some
diodes to provide the driver collector voltage. This was a 5V 30A supply
and I was trying to minimize loss. When TTL was in vogue...

That is a very good idea. You can do something like that very cheaply
by just providing a small extra filter cap that is fed by two extra
diodes, to make a positive supply that doesn't have the full ripple
sag of the big caps.

I would build the thing with a 15 or 16 volt transformer instead of
the 18 volt one specified, unless you have lots of trouble with low
line voltage.

If you do use an 18 volt one, you can lower the peak currents and cool
the transformer, capacitors and output transistors off by putting a
big resistor in series with the transformer primary, such that at full
load you just barely have enough DC to keep the regulator
functioning. You still get the heat, but it is dumped into a
resistor, instead of those other components. It also reduces the
current thump when you turn the thing on and have to both charge the
caps and handle transformer core saturation.

I think you can also improve the load transient response by putting a
10 ohm resistor across the output transistors, base to emitter, and a
100 ohm resistor base to emitter on the driver transistor. I haven't
calculated the closed loop frequency response of this design.

--
John Popelish