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Checking out diodes ... ?

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john1

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Hi,

I have a modest collection of diodes and i would like to know if there is a way to estimate the Peak Inverse Voltage.

I can see the forward voltage drop, it may be possible to get some idea from that. I think that the forward voltage drop is usually slightly higher on higher voltage diodes, but i am not sure. And it may be that newer designs have lower forward voltage drops, so the age may be a factor too.

I can tell at what forward current they get hot to the touch, again newer designs may run hotter than earlier ones, so again, age may be a factor.

If the Peak Inverse Voltage comes in with some sort of change of characteristics, then it might be possible to make up some arrangement to indicate this.
I don't know what may change, or may not change before damage occurs, but something may happen at or near that point.
Maybe the 'capacitance' of the diode might alter, or even 'stop altering' when the diode is at or near its PIV ....
Maybe some slight leakage increases just before the PIV ...

Maybe the PIV breakdown is an 'avalanche action' and once started, cannot be stopped except by very quick removal of the supply ...

Personally, i do not know of any way to estimate the PIV of a diode.
The only way i have to make any decision, is to pick out ones which look and seem identical, as far as i can tell, and then test one until it breaks down.

This is most unsatisfactory, and i wonder if there is a way to estimate the PIV on my un-marked diodes.

I could send pictures if it would help, but i don't see how it would help.

Regards, John :)
 
From what I can recall?, from a VERY long time ago, you can do it with a variable high voltage supply, and a current limiting resistor. Feed the diode via the current limiting resistor and a micro-ammeter, then turn the voltage up until you start to get current flowing, then back it off and read the voltage of the supply.
 
Hi,

That certainly sounds workable,
i will give it a try,
might be a while before i get round to it, when i do i will
come back with what i find.

I have a shoebox full of various diodes from here and there, mostly
unmarked, or with markings that no longer seem to mean anything.

Cheers, John :)
 
If you have a 'scope you can set up a simple curve tracer to watch for the "knee-point" and prevent too many silicon casualties. Nigels way is simpler, depnding on what gear you have access to.
 
Theres a knee point ... ?


I have looked at various manufacturers curves,
but never seen one.
Maybe they just dont take the voltage that far.
 
I was wondering about the capacitance effect,
that might be another possible alternative.
 
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