24 Feb
2002
24 Feb
'02
1:50 p.m.
On Sun, 24 Feb 2002, Richard Erlacher wrote:
I didn't mean current limiting for the entire
supply, but rather just
for the Termpwr. I'm no longer sure whether it's to be limited to one
ampere or a half an ampere, or what. I never used to forget once I
had things written down, and this is specified in the standard.
Apple probably left out the diode so they wouldn't have to put in the
fuse. It does cost money, after all. Diodes seem to make pretty
cheap fuses, too, unless there's no fuse in the circuit, in which case
they'll hold up until some major component fails. If there's a fuse,
the diode will, of course, fail first.
The Adaptec AHA-1542B reference manual I have on hand lists available
terminator power current as 800ma. min, and 1.5A max. The AHA-1542C board
I had laying around has a 1.6A fuse, but the newer boards use a
self-resetting surface mount device instead. IIRC, the standard requires
some sort of current limiting device to be present for termpower.
-Toth