One thing you need to know about the "literature" on
transistor values is that beta's are measured at very
specific points on the transistor's operating curves.
If you are using a little hand held transistor tester,
it is highly unlikely that you are measuring at the same
operating point as was used in the literature.
A full blown curve tracer, is necessary to duplicate
the manufacturer's literature.
Critical applications of transistors require that you
use the full curves, and draw in load lines that represent
your operating conditions.
The purpose behind the little transistor testers is
two-fold, 1) to get your money, and 2) to test if
the transistor actually has any gain. Some gain usually
indicates a working transistor.
When you use a DVM to do a junction test on a transistor,
all you can tell for sure is that you found junctions that
do, or don't, behave like diodes.
Junction tests tell if the transistor is shorted, or open,
but not if it is good.
-Chuck Harris
Tim Phillips wrote:
toggle quoted message
Show quoted text
from Tim P (UK)
Sorry if this is more 'Electronics-101' than 'TekScopes', but I'm curious.
I sometimes find when checking transistors (on a Peak DCA55) that the Beta
is outside the range specified in the literature. Towers International is
popular in UK.
F'rinstance I'm looking at a 1S2 with a non-working pulser and a 2N3904 has
a Beta of 65 as against Towers 'minimum 100' I also see instances of
common-or-garden transistors with published Beta of -say- 200 and measured
at -say- 450.
Does a low or high + / - 50% mean an aging transistor? I know Tek had good
reasons for what they did, but these examples were not 'selected' or
TekSpec.
(Don't worry, I'm not about to shotgun the transistors and THEN call for
help !!)
many thanks
Tim
Raymond Domp Frank
Dale H. Cook