Re: Adapting this NSC app note for my +150V regulator

Michael A. Terrell wrote:
Jamie wrote:
Jim Thompson wrote:

On Thu, 27 Mar 2008 17:08:31 -0700, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:


Well, then toss them. I would not trust them for switching either. Who
knows what went wrong during production and when they will fail.

Virtually all modern transistors will self-oscillate if applied
incorrectly. I'd play my money on bad design.

...Jim Thompson
Well, think what you want, the units were tested in 2 different
jig circuits and failed at aprox the same current in common
emitter test and emitter follower test. Playing with different
biasing and voltages didn't seem to matter. Only the Ice seem
to be a factor.
If we attempted to suppress the noise it would place an attenuated
dip in that region of linearity of the circuit. Basically, it was
almost acting like a tunnel effect at that point.

They do seem to work well for switching how ever. We send back a
few to the supplier for them to look at before they were going to
replace them. We had made a large order of these which were fairchild
made. They were suppose to send us a different vender of the product but
we ended up with Fairchild again with a different date code. These were
fine.

I kind of think that many look at the 2222 as a switching transistor
and not much used in linear applications with this family. Maybe the
fab house also thought this and didn't care. Just correct the problem
and call it a day.


I agree with Jim. I have used the MMBT2222 in a lot of analog
circuits and never had any oscillate, if the rest of the circuit was
right.

As far as your jigs: Do you have the specifications for them? Lead
inductance? Inter electrode capacitance? Did you compare the gain of
that batch against the ones that work, as well as the fT? Sometimes a
bad circuit works great with a part that barely meets specs. Replace it
with a better quality component and everything goes to hell.


To analyze the case better it would have been good to check the suspicious lot for hfe and ft. Chances are that one or both may have been better than in the data***. Maybe too much for the jig, but I don't know the jig.

--
Regards, Joerg

http://www.analogconsultants.com/
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