[sdiy] SSM2164 protection

[ASSI]

On Wednesday 02 March 2011, David G. Dixon wrote:
> OK, where's the flaw?

If you must ask, there are several. :-)

Count how much capacitance is downstream from the switch.  Now consider that 
all capacitors are discharging through the single module that decides to 
latch up first... at least it'd probably protect the others from failing, 
but Murphys law will make it the module you can spare the least.  A latchup 
happens very fast, so by the time your protection switch knows that 
something is wrong the modules may have well given up the ghost already.  
Also that switch doesn't protect against reverse voltage at all, the body 
diode will open and if you prevent this, there's still the path to the 
unprotected ground rail.  Failsafe power distribution is hard to design and 
costly to implement due to the multitude of possible failure modes, even if 
you consider only a single mode for each failure event (you usually don't 
have that luxury, either).


Achim.
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