25 Feb
2002
25 Feb
'02
5:25 p.m.
Yes, but since there's a standard to which most manufacturers give at least a
little attention, the fact that a computer's 5-volt supply may be limited to
50 Amps while a CDROM drive may have a supply limited to 2, makes the notion
of inherent current limiting due to power supply design somwhat limited as far
as its usefulness in limiting the current to the SCSI TermPwr line.
Anyway, the standard goes into considerable detail about this seemingly
uniteresting (to the folks at Apple Computer Co.) detail. It's published on
the web, so I invite anyone who wants to know this stuff to have a look.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Monday, February 25, 2002 12:44 PM
Subject: Re: Apple SCSI TermPWR; Was Re: This is funny (ebay)
>
> I didn't mean current limiting for the entire supply, but rather just for
the
Sure... The point is, though that the current you can draw _is_ limited.
in
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
Well, since when have Apple ever stuck to standards? I am actually
suprised the PCB doesn't have a place for a fuse as well, but it doesn't.
> all. Diodes seem to make pretty cheap fuses, too, unless there's no fuse
> 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.
This is doubtless the result of much practical experience ;-)
-tony