>
>> >Are people claiming one diode goes to threshold and then the others start
>> >being forced to threshold as that single diode avalanches? Is that the
>> >mechanism that causes voltages to be "shared"?
>>
>> That's how I'm reading the argument, Tom.
>>
>> I repeat: if the data sheet doesn't say 'controlled avalanche device',
>> don't rely on it being so.
>
>"Controlled avalanche" means the diode has a breakdown curve
>knee, where reverse current suddenly skyrockets.
? The breakdown region is defined but not all that sudden. It means
that the transistion is smooth and doesn't make any sudden moves.
>Engineering
>references from Motorola state that "Normal circuit operating
>voltages should be below the minimum breakdown voltage" (which
>is found by a test that establishes a "knee" in current reached
>when raising the reverse voltage).
>
>Now they don't say these knees are all the same, they just say the
>diode has at least this high of a knee in the reverse current curves.
>They don't even specify the current.
>
? That's because the current varies along the knee, Tom. However, there
is a max. reverse current rating - typically about 5uA.
>If you depend on this knee establishing the division, then it seems
>you are breaking the design guideline that normal operating
>voltages should never reach that point. They warn if you constantly
>avalanche the diodes, life can be reduced.
? If you exceed the maximum reverse current spec., certainly.
>
>So let me ask again, what keeps one or more diodes from being
>operated contrary to manufacturer's specs and suggestions when
>you series a whole string with nothing but diodes?
>
? You select diodes that are have similar measured avalance voltages,
put them in series, make sure the actual piv in the circuit is well under
the total measured piv in the diodes, and let her rip. I have been doing
this for decades. . Sure, it takes a little extra time. However, it
works fine. .
>
- later, Tom.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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