Wonderful, I might learn something here.
Here are some more details about the existing parts.


I use an existing center tapped transformer which gives twice 10.7 V. I also
have 4 caps of 167 000mF at 7.5 V (which are currently hooked up for 15V max
voltage) and two fat diodes. The transformer is probably good for 25 to 30A
( it has a 3.5 X 4.5 X 6 inch core).

If the 15 V I get right now at my filter stage is barely enough for decent
regulation I could double that (and also use a bridge rectifier) but then I
would have to regulate that higher voltage down to the 13.8V I will most
often use.

I looked at the design http://www.rason.org/Projects/powsupply/powsupply.htm
that Tracy had suggested and it looks manageable to me (the Astron design
someone suggested have additional windings on their transformers which I do
not have on mine) but I do not have the expertise to change parts in the
design to accommodate the higher voltage and current I could get out of my
transformer. I am not sure if I only have to change the current limiting
resisitor at the 723 as well as the resistors which determine the output
voltage or if more elaborate changes involving the 2N3055's are necessary.

regards Uwe







in article , John Popelish at
wrote on 2/2/04 7:02 PM:

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.