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.

- Franc Zabkar
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