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 ?


An interesting observation; some thoughtful speculation and perhaps a few
experiments may be useful.

1. perhaps the dominant failure mode in some equipment happens on the
negative half cycle of input power, especially in switching applications.

2. perhaps in some areas, power line glitches occur more often on the
negative half cycle.

3. perhaps the devices are manufactured with a deviation of thermal
characteristics in the region of the negative arm making them more
prone to failure there.

It would make an interesting science project for a student to accumulate
a number of encapsulated bridge rectifiers (I'll leave it to others
to outline the statistics) and build a shorting fixture that randomly
shorts the device (in a symmetrical fashion, making sure that it is not
synchronized with the power line) and run the experiment. If the
anomaly is verified, then deeper investigation is in order such as
microscopic examination of intact good devices and post mortems on
bad ones. What with the _vast_ amount of trashed electronics these
days, it shouldn't be difficult to accumulate hundreds of rectifiers
for the endeavor.

Also a 'net search on "bridge rectifier" "failure modes" may turn
up something.

Regards,

Michael