Zeners Short Circuit Problem

[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

 

[RODALCO]

Hi Ahmet,

Were these zeners connected up correct ?? with the circled line towards the positive ?

[+] [I<] [ load resistor] [-]

Were these zeners all from the same batch ?

Whoever sold you them may have had a bad supplier.

The 5V6 or 9V1 are common values which are available and should have no particular problems.
In the opposite mode they conduct at 0.6 Volts.

Try a 2V7 and 3V0 in series (which gives you 5V7 total )

 

[proksima]

Zeners shorts circuit

Thanks for your reply first,

Yes, we use our Zeners in a right way(correct polarities, correct usage in a capacitive supply, etc.) and controlled all diode batches for the weekly periods.

However we can't find the main reason which triggers the Zener diode short circuit problem.

 

[audioguru]

1.3W is probably the absolute max the zener can dissipate in a nice cool room with free ventilation and with very short leads soldered to large-area copper runs on a pcb. Something in the operation of your zeners is different and is causing them to overheat.

 

[Roff]

Can you post a partial schematic?

 

[hjames]

One manufacturer seems to indicate that zeners (in the context of TVS devices) that fail due to overstress, tend to short: page 75

https://www.onsemi.com/pub/Collateral/HBD854-D.PDF#search="zener doping defect diode testing"

 

[Roff]

One manufacturer seems to indicate that zeners (in the context of TVS devices) that fail due to overstress, tend to short: page 75

https://www.onsemi.com/pub/Collateral/HBD854-D.PDF#search="zener doping defect diode testing"

Yeah, I'm wondering what "capacitive supplies" means. The term makes me think of inrush current, and what it could do to a zener.