"b" wrote in message
...
On 11 ene, 20:48, Franc Zabkar wrote:
On Mon, 11 Jan 2010 08:55:58 -0000, "N_Cook" put
finger to keyboard and composed:



Franc Zabkar wrote in message
.. .
On Mon, 11 Jan 2010 08:25:42 -0000, "N_Cook" put
finger to keyboard and composed:

But,unlike zeners , are they guaranteed to go short circuit if they
end
up
in what becomes a sustained overvoltage rather than just a transient
situation ? or 2 different clases of TVS ?

I watch various hard drive forums. HDs nowadays use TVS diodes on
their +5V and +12V rails. A sustained overvoltage from, say, a 19V
laptop adapter always (?) shorts the 12V diode, unless it is protected
by a fusible zero-ohm resistor.

- Franc Zabkar
A zener would normally burn up/ go open circuit in overvoltage but do
VTS
normally (but not guaranteed) go short thus providing crowbar protection
if
fuse/fusible R/ current limiting/ps shut down, upstream. 80 percent/90
percent/ 99 percent of the time go s/c rather than o/c , any
guesses/knowlege?

I would think that they would go s/c, but will eventually go o/c if
the fault current is sustained.

The TVS failures I've seen have all been s/c because the PSU has shut
down.


thanks for all the replies. so, seems like this is purely for
protection while zeners can be sued for regulation.
the one here is s/c and the psu was utterly dead. there are a few
bulged caps and its a cramped crappy design so no real mystery. it
must have gone s/c as the rails crept up and it could no longer handle
the suppression of transients. Owner reported strange noises before it
died.
-B

Hello B,

Here's a description for TVS diodes that talk about the difference between
them and zeners.

http://www.semtech.com/images/datash...tvs_diodes.pdf

Shaun