Arfa Daily wrote:
When a diode power bridge - discrete devices or four-legged package - fails,
it's almost invariably one diode in the 'negative' arm which goes short
circuit. Any thoughts on why this should be, rather than any one of the four
failing at random ?

Arfa


Ok Arfa,

I think now that I have posted physical theories to the last two
(plugtop; xmas light) I might have a similar *physical* answer to the
diode anomaly.

Sinking away heat from the diode PN junction is more efficient with a
large amount of ground plane to connect to which is the case with the
negative half of the bridge. These diodes will run with a higher Vf and
hence a higher power dissipation than the remaining diodes on the bridge
given that both positive and negative halves will be conducting the same
current. Where fault conditions exist on the DC side of the circuit,
these harder running diodes may be the first to fail?

Dunno.

On the other hand, I tried looking for conditions for thermal runaway in
bridge rectifier diodes and came up with the following link
http://www.freepatentsonline.com/6731030.html
but can't say from that which half of the bridge would be suceptable to
shorted failure.

--
Adrian C