Marc Price wrote:
Seen as the Tesla coil mailing list is down i thought i might ask this
question here
i tested 2 x 2n3055 transistors and i read that you need to match the 2
but what
i dont know is, do i need to have them exact or just close.
transistor 1 gain Hfe = 123
transistor 2 gain Hfe = 194
Any ideas
Marc :-P
You'll have to be more specific than that. It depends on the details of
your application which none of us know. Perhaps you're trying to make a
low offset differential amplifier. In that case I'd be at least as
worried about Vbe matching as I would about Hfe matching. You can, of
course, have very good Hfe matching and bad Vbe matching ( take 2
transistors which are identical in every way except 1 has 2x the emitter
area, now you have 18 mV of offset at room temperature and the offset is
proportional to temperature).
My guess is if you're using them in a tesla coil app you probably don't
need "good" matching but then again I don't have the details of your
circuit.
-Dan
