Electron wrote:
> what happens when a negative swing at the base of a NPN transistor reachs
> the break down voltage?

Generally, a reverse-biased B-E junction will function as a (noisy) zener
diode somewhere in the range of 10-20V. Obviously, if any significant curre=
nt
is allowed to flow in this mode, it will dissipate a lot of power in the
transistor. However, I have seen circuits in which a transistor was
deliberately operated in this mode as a noise source (e.g., analog music
or drum synthesizer).

> Does it turn on the transistor, and then as long as the current is limite=
d
> to a safe value, it won't damage it or do other weird things?

No, the transistor doesn't turn on; the reverse current in the B-E junction
doesn't inject the right kind of carriers (if anyt) into the B-C junction,
which is also more strongly reverse-biased than usual.

-- Dave Tweed
--=20
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