On Wed, 30 Oct 2002, Jim wrote:

*>   "You can't damage a 317 easily "
*>
*>The problem comes in when big caps (or when
*>caps charge from low-z sorces) supply loads
*>through unintentional paths (like when seen in
*>reverse bias conditions) that may pop the bond
*>wires inside the device package ... no SOA here.

Maybe but a reverse connected diode across the device (output to input)
will do its job and in my experience 317s are extremely tough. The fact
that there is no high current path to ground helps. I had trouble with a
product (not mine) that supplied a troublesome connector from a 317T. The
connector would short in some units. I've never seen a failed 317 in any
of those, only the thermal fuse in the transformer went.  These were 800mA
supplies I think. The internal protection in the 317 is pretty good even
if you put a dead short across the output. It's SOA + overcurrent
protection (probably by controlled beta or something like that). The only
way to kill it is overvoltage ('back' voltage) from the output to the
input. SLA batteries can do this if the bridge or other parts upstream are
shorted (in a charger application). Otherwise it is very hard to kill
them.

Peter

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