Diode Dilemma?

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Lenp
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Diode Dilemma?

Post by Lenp » Sun Oct 29, 2006 10:58 am

Here's a thinker's issue!
There is a family of diodes, the 1N400X family that are commonly available as 1N4001 with a PIV of 50V to 1N4007 with a PIV of 1000V. In any given manufacturer's price listing all are the same (or nearly) the same price.

The manufacturer usually lists all of them on the same spec sheet so the specs are the same with the exception of the PIV.

So...
1. Why do they make the lower voltage units when the higher voltage unit is suitable.

2. Even if they were 'graded' at the time of production, if they are comparable in in their specs and price, why would you buy the lower PIV unit?

What am I missing here?

Len

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Chris Smith
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Post by Chris Smith » Sun Oct 29, 2006 1:25 pm

They are not actually identical except for their PIV variance.

The higher the PIV, usually the thicker or longer the material is [mass] and thus the reverse time, start up voltage, forward flow, etc is slightly different.

This MAY affect the circuit.

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Bob Scott
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Post by Bob Scott » Mon Oct 30, 2006 7:59 pm

Len,

I only see these things used as rectifiers, so I just keep the 1N4007s. IT's like the TO-220 power transistors: The TIP41C NPN and TIP42C PNP make nice universal one-size-fits-most replacement T0-220 power transistors.

Bob :cool:

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HighFrequency
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Post by HighFrequency » Mon Oct 30, 2006 9:08 pm

Maybe you have other sensitive components behind the diode, and the diode could be another weak link, kind of like a fuse?
There is only one correct answer, mine.

cato
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Post by cato » Sun Nov 12, 2006 5:49 am

I think upon closer inspection you will see that reverse voltage is not free. It comes at the expense of some other parameter; junction capacitance for example.

Accordingly, there are many applications where the 50V part will work and the 1000 V part will not.

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Joseph
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Post by Joseph » Sun Nov 12, 2006 2:17 pm

Yeah, I bought some 1N4001 diodes and tested their reverse bias up to 600V. Even there they were not leaking yet.

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