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Re: coil running of car battery(s)?

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

If only I have killed many of them, usually from spikes in the gate,
are very susceptible to HV..

Although the circuit is similar to the one I used, being 30+ I have
used the good old 2N3055, which is apparently much easier to kill, maybe
my experience, but i've only killed a couple in that circuit, and most
them are from shorts whilst playing, not "in service". I do have a 4nF
and a reverse diode across then though.


	The shorts are probably due to "second breakdown" in the forward
direction at the peak of the voltage spike.  When the voltage goes above
a critical value the collector starts to draw a lot of current and
enters a negative resistance region where the current "run away" and if
the circuit resistance doesn't limit it the transistors will short.
There are 2N3055H's which have a somewhat higher breakdown I think, but
still a lot less than that of the 600V or 800V that transistors intended
to drive the horizontal deflection circuits of a TV. Lots of different
ones available as well as transistors intended specifically for ignition
coil drivers.