Re: solid state magnifier...accidentally...cool!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
> 
> Tesla list wrote:
> 
> > Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <evp-at-pacbell-dot-net>
> 
> >         Won't work.  The driver feeds a high current through the
primary and
> > then interrupts it suddenly, producing an inductive voltage rise as the
> > energy stored in the primary is released.  The OP AMP won't allow that
> > rise.  I have found that, for 12 V power source and typical ignition
> > coils, the voltage can go as high as three or four hundred volts.
> > Usually use a shunt capacitor across the transistor to control the
> > swing.  Value determined by careful "by guess and by gosh", usually of
> > the order of 1 ufd or more.
> 
> The same idea used in classical induction coils. Without the capacitor
> most of the energy is dissipated in the opening sparks at the primary
> interruptor.
> In a solid-state induction coil, the capacitor can be used to limit
> the voltage over the driving transistor, maybe allowing the use of
> a low-voltage transistor as a 2N3055 in a safer way.
> 
> Antonio Carlos M. de Queiroz

	Of course, the typical automobile ignition system IS a classical
induction coil.  In my experience, limiting the primary voltage rise to
less than of the order of 200 volts limits the peak output voltage, but
perhaps there are coils which would work fine with less.  The 2N3055 is
a pretty crummy device compared to better parts which are available at
reasonable prices.

Ed