Re measurements

[Ian Fritz]

Hi all --

I set up a breadboard circuit to measure transistor Re values as
described in an earlier post. Here are some results. So far I've only
looked at NPNs. Since Re isn't usually spec'ed, I have no idea whether
there are large variations between manufacturers or between batches. The
technique works pretty well, though. Also listed are the Beta values
measured by DVM.

Part	Re(Ohm)	Beta
______________________

CA3046	5.0	59
CA3083	1.3	190
2N3904	1.7	110
NTE42	2.4	310
AD818	2.4	220
LM394	1.1	290

The AD818 is obsolete, but I included it for comparison since it was
used for a number of old EN projects. 

Of course, there's more to converter performance than these two
parameters. Matching must be looked at closely.

Maybe I just got a good batch, but the CA3083s I have looked at have
very tight matching of Vbe (generally better than 0.5 mV), so they might
be a good alternative to the now almost obsolete CA3046.

  Ian