SMPSU IC explosion... (UC3844)

Jules Richardson julesrichardsonuk at yahoo.co.uk
Wed Nov 30 19:32:09 CST 2005


Random failure of the weekend was a UC3844 IC in a switchmode power supply - 
with a very loud bang, the entire top of the chip blew off, but there's no 
*obvious* sign of any other failure within the supply.

This was one of two such supplies in a Sun RAID disk controller; the two do 
current-sharing under normal conditions - but the unit will run on one supply 
if the other fails, which is exactly what happened here. Leads me to 
*tentatively* say that the RAID unit itself is 100% and the failure was 
totally in the PSU.

So, given that assumption for now, anyone know of a likely fault in a typical 
SMPSU that might cause such a catastrophic chip failure but no other obvious 
damage? Seems like a strange one to me, but I assume that something else in 
the supply has failed and the chip just couldn't handle it. Whilst knowing a 
bit of SMPSU theory (and practice), I'm not familiar with the UC3844...

Of course maybe it was just time for that chip to die (it was at startup, and 
this in a server which had probably only been power cycled a handful of times 
in its life), but it sure was noisy about it.

Shame Sun don't publish schematics!

cheers

Jules




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