Jim Levie wrote:

On Wed, 09 Feb 2005 08:21:33 -0800, Ed Angell wrote:



Sorry for the OT post, but I don't know a better group of knowledgeable
folks to ask.

As long as a triac is run within it's published temperature limits, is there
any shortening of their life due to running warm ??



Yes. The lifetime of a semiconductor device is directly related to its
operating (junction) temperature. The cause of eventual failure (assuming
operation within the envelope) is a result of migration of material
within the junction, which is exponential with temperature as I recall.

Whether the reduction in lifetime is of concern depends on how hot the
device runs, how close to rated limits it is used, and what transients it
will be exposed to.



My brain is swiss cheese these days but if I remember correctly, aren't
Triacs and SCRs a device such that the higher the temp, the lower the
internal resistance? I seem to remember something about people putting
them in parallel and a vicious cycle starting where one would conduct a
higher percentage of the load, heat a little more and drop internal
resistance, therefore heat more until it blows.

Just curoius...one of these days I have to switch an inductive load on a
forging machine somehow. Output is about 6000 amps at 3 volts. Makes
the theoretical (no loss) input about 75 amps at 240 V. The problem is
that things are so highly inductive, any digital switching would have to
be far greater than the 75 amp rating. That gets spendy. If you could
gang the darned things, the cost would be MUCH better.

Any ideas on a cheap but digitally controlled solution? In the old
days, one might use mercury relays. Regular relays will fry and lock.
Of course there are ways to suck up the initial inductive load but I'd
rather keep things simple.


Koz