Albert wrote:
OK, thanks to all who provided some guidance in the original post (see
'low voltage drop transistors for power supply' post.

Clearly, this was a 12v supply and not a 13.8v supply. The actual
output current ratings are not known, the only hint is that the
original meter was a 25 amp meter.

The transformer is much larger than 100 va and is actually larger than
a 200 va unit (based on core size). When I tore down the rest of the
assembly, I found more shaky stuff including sockets for the
transistors that were soldered, several etch cuts and lifted run on
the PCB, meter shunt was missing (probably discarded when the original
pcb was replaced). In other words, it probably needs a complete
redesign rather than using any of the original parts and pc boards.

I ran LTC's power supply design software and it came up with a 13.8
volt output switching supply that will supply 14A with the existing
power transformer. It uses the LTC1775 switching regulator, 2 X
Si4410DY mosfets, an 11 uH inductor and a couple of 1N5818 schottky
diodes. The supply itself (not including transformer losses and
rectifier losses) provides 98 percent efficiency at 14A output.

So, I'm considering building up this switching supply.

I need suggestions for a schottkey bridge rectifier that will handle
20A or more. I find the diodes themselves are readily available, but
I'd like to have a bridge assembly if possible.

Any suggestions??

Sounds like you don't have to change a thing- the 3055 is operated in
"inverted" mode and this will give you the lowest series voltage possible:
Please view in a fixed-width font such as Courier.

Inpn
---- Iload
3055 -----
V+ --+------------ e c ------+-----+- Vregulated
| \ / | |
| ---- Ipnp | |
| b ---- | |
| 2955 | Rbn | |
+----e c ----+----/\/\--+ |
| \ / |
/ ---- |
Rbp b error amp |
/ | /
\ | /| \
| | /+|------------ /
+------+------- | \
\-|--Vref |
\| |
|
|
---
///



Light loading supplied by PNP 2N2955-

Rbn sized to cut-in NPN at heavy loading for boost-

At MAX Iload NPN is inverse saturated- very low VCE

Ie,npn=5A Ib,npn=5A - Inpn=Ic,npn=10A

Ic,pnp=Ib,npn + Ipnp= 5A +10A= 15A @ Veb,npn =Low Pdiss

Iload/MAX=Ic,npn + Ipnp= 20A

Vbc,npn@5A - 12V
Rbn= ----------------
10A