Rich says:
> The capacitance of a P/N junction is not fixed, but decreases considerably
>as reverse potential increases.
But most of this change is at low voltages, depending on the gamma of the
diode. Up at these piv's, there's very little change in capacity for several
hundred volts change. The change would make the volts increase across the
diode, too.
> The division of the reverse potential is controlled by the avalanche
>voltages of all the diodes in a series string
It could be - or it could be the capacity, depending.
A bit of pontificating now. I've been in the semiconductor industry for over
20 years now, and the first thing is - DON'T TRUST THEM! Where else is there
an industry that says 'Yes, give me $250K, and I'll do a design for you. If
it doesn't work, I'll have another go for another $150K.'
If the data sheet doesn't say 'controlled avalanche device', don't assume
that it is. Might be this week, may not be next. Might be from this
manufacturer, and not from another.
Any parameter not specified on a data sheet can't be relied on for
repeatability from device to device (and even some that are!)
Why do you think the military have JEDEC data sheets for devices? they've
learned!
Diodes of this class will be tested just about as fast as a handler can go -
probably 50 to 100 per second, since you need only to test forward drop and
piv. For a 1000 volt piv diode, you'll test with 1kV reverse; is the current
less than x microamps? if yes, bin 1, if not bin 2.
You might go 'is current more than y microamps - if yes bin 3' to sort out
the short circuit ones; bin 2 can then get tested for 800 or 600 or whatever
volt diodes.
But there won't be sophisticated testing. If the diodes come on a bandolier,
there's a good chance that they'll be from the same diffusion batch, maybe
even the same wafer, but that's not guaranteed.
73
Peter G3RZP
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