Regarding semiconductor equivalence...

[Armen Forget]

Hi. This has confused me for some time now. Let's say I have x number
of general purpose NPN BJTs (or any other semiconductor device). Their
model #s seem strange (to me) and are relatively hard to find. So I
checked their NTE equivalents through their catalog, and they're all
the same: NTE123AP. Now, the 2N3904 (which I've got plenty of) also
has the SAME NTE code! Does this mean all models are equivalent? Can I
just substitute the 2N3904? Or does NTE make their devices superior to
a whole set of devices to increase compatibility?

Someone please help. I'm tired of looking for odd models of
semiconductor devices. And thanks for taking the time to read this
boring letter.

Armen

 

[Watson A.Name - "Watt Sun]

In article <5abd2e45.0310140738.172a4bf1@posting.google.com>,
armenforget@yahoo.com mentioned...

Hi. This has confused me for some time now. Let's say I have x number
of general purpose NPN BJTs (or any other semiconductor device). Their
model #s seem strange (to me) and are relatively hard to find. So I
checked their NTE equivalents through their catalog, and they're all
the same: NTE123AP. Now, the 2N3904 (which I've got plenty of) also
has the SAME NTE code! Does this mean all models are equivalent?
Can I just substitute the 2N3904? Or does NTE make their devices
superior to a whole set of devices to increase compatibility?

No, you cannot. The NTE is supposed to be equal or better. For
instance (only as an example, may not be the actual values), Your
unknown device may have a minimum current gain of, say, 200, typical
of 250. The NTE data may show the NTE123 substitutes, but it has a
minimum gain of 200, typical 300, which is fine for substitution with
yours _and_ the 2N3904. But the minimum gain of a 2N3904 may be 120,
typical 200. So even tho it seems to be a sub, the minimum gain would
be much less than your unknown device.

So your substitution procedure, in general, is not a valid method.
However, with more detailed knowledge, such as the circuit that it's
going into, etc., you might be able to make a good estimate of whether
or not this kind of sub will work.

Someone please help. I'm tired of looking for odd models of
semiconductor devices. And thanks for taking the time to read this
boring letter.

We've also pondered this kind of thing ourselves. Some of us have
gone thru that learning process and found out the foibles in it. So
it's good to ask, so you can find out before, and save yourself the
trouble.

Armen

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