Gerhard Fiedler wrote:

>David VanHorn wrote:
>
>  
>
>>>And why  1N4148s are dying, 1N4007 not?
>>>      
>>>
>>Interesting question. Obviously the 4007 can handle more energy, but that's
>>not likely the cause.
>>    
>>
>
>Could it be that the voltage rises too fast? That it reaches values deadly
>for the 1N4148 before the diode can open?
>
>Gerhard
>
>  
>
My conclusion was that with a max reverse voltage rating of only 100V, 
the occasional spike
that exceeded 100V with the relay's collapsing field (these are 12V 
relays), caused a punch-through
of the junction, causing the short, as we found that all failures were 
shorted 1N4148's. Since the
1N4007 can handle a 1000V spike, no damage can occur. But the 1N4007 is 
much slower than the
1N4148, and we needed to block the spike more, so the TVS is used.

--Bob

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