Zener Shorts

[proksima]

Does anybody have a recent problem regarding to THT Zener Diode (especially 9V1 and 5V6) (They behave like short circuits)
Actually we faced with such a problem where we use 1.3W Zener diodes below their electrical ratings in our capacitive supplies (In our boards our worst case Zener condition is 600mW ).

We observe this problem in the first function test during manufacturing or in the life test also so the failure rate doesn’t depend on the working period of the electronic board.

I do appreciated for all kinds of comments.

Best regards,

Ahmet

[vtech]

I use variety of THT or SMD zener diodes in different applications from SMPS to Audio/video & RF circuits with no problem.
There is no reason for a zener to fail while operating within it's breakeover ratings & design parameters.
You may be experiencing faulty batch components or perhaps a design issue where the ratings are exceeded due to momentarily overload line coditions/etc

Your worst case of 600mW calculation may be skewed in real testing.

Ray