19 Jan
2010
19 Jan
'10
8:30 p.m.
Tony Duell wrote:
I wasn;'t just thinking of comptuers. Things like VCRs, DVD players, etc,
have nasty sheet metacl covers now that draw blood.
Off-topic, but modern consumer electronics
(particularly the cheap 'own
brands' tends to be assembled in thin sheet-metal cases with edges that
will give you a nasty-ish cut if you catch them.
I've stopped using the really cheap PC cases. The Antec 300 I'm using now seems to have had the metal edges rolled over at
least once, which
pretty much leaves it with smooth rounded edges that have the cutting
ability of a wet paper towel.
Hmm.. I prefer it if even those are cool enough to touch without a nasty
burn. I always feel that too-hot == unreliable.
A diode should be dropping 0.7V or so. For that to dissipate 10W, it must
be carrying about 14A. That's not small. Ditto for thyristors.
Modern components shouldn't get hot enough to
burn you :-).
Exceptions: power transistors (esp. BJTs). SCRs. Big diodes. Well, just
about anything that's handling more than about ~10W of power really...
That said an un-heatsinked 7805 running at 1A output with a 12V input
will run surprisingly hot, too, and that's only 7W. I've seen 7805s hit
True. The only ime I run a 7805 without a heatsink is when a 78L05 would
have done :-), but I'm using the larger-cuirrent version becasue I had
one in the junk box.
Glassfets are
another matter.
Mmm, vacuum tubes. "After turning off main power, wait 15 minutes for
valves to cool." And an IC that has developped internal shorts can
get hot
enough to burn you, some DRAMs were prone to this.
A few old 1k*4 SRAMs did this too. 2114 anyone?
Those things were nasty little buggers. If it wasn't a bad bit, it was a
dead bitline, address line or just a dead chip shorting the power bus.
Must be one of the least reliable SRAM chips ever made. Yes, I was thinking of bruns from the soldering
iron, or something heated
by it Most of the time it's when I am soldering a piece of wire to a
large-ish metal object (pin of a 4mm plug) and I don't let it cool for
long enough before taking it out of the vice.
I seem to do that with startling regularity... Somehow the concept of
objects touched by soldering irons also being hot hasn't quite sunk in yet.