> Michael Rigby-Jones wrote:
>
>      <snip>
>      > As for the question of what is a TRISIL. Basicaly is a
>      bidirectional
>      > crowbar device (Like 2 SCRS) that clamps both rails together
>      (To within
>      > 0.6V) one the breakover point is reached. These things come in
>      0.5kW and
>      > 1.5kW (Yep thats correct) versions (surface mount 0805, and
>      SOIC8!). I love
>      > these things
>      >
>      > Dennis
>
>      DigiKey calls these Transient Voltage Suppressors (TVS) - they
>      come
>      unidirectional or bi-directional.
>
>        Mark
>
> If it acts like back to back SCR's, then I'm guessing that this really
> is a crowbar device, i.e. once triggered it remains conducting untill
> current is removed?  If so not too usefull for spike suppression...
>
> Mike Rigby-Jones

TVS's act just like a fast, cheap, very high power Zener, they're a
little sloppy on triggering voltage (not quite as precise as a Zener, or
at least weren't at one time), these work well for Auto circuits.  A TVS
won't clamp down to 0.6V (maybe a Trisil is a different beastie?)  TVS's
are rated by power & Vbr (breakdown / avalanche voltage);  1 pSec
avalanche time for unidirectional units, the bidirectional's are slower,
and at $0.72 in onesies for the 1.5kW units, you can do worse.  General
Semiconductor makes the ones I've looked at, other co's make these;
http://www.digikey.com/EC/V3/250.pdf for Digi-Key's catalog page, FYI.
Other places may be cheaper. <G>

The wattage rating IS, btw, a "Peak power pulse" rating - I wouldn't try
to use one at a steady state power dissipation of 1.5kW, "it wouldn't be
pretty!" - I haven't blown one up yet, I'm sure someone will here <G>

  Mark

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