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: "spoonMAN by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<spoonman534-at-yahoo-dot-com>
> 
> <snip>
> 
> > Of course, I'll be using a 555 driven 2N3055....
> > However, I'm hoping to aquire some higher power mosfets
> > soon, the 2N3055s
> > don't like anything over 20 volts. They are just little
> > heaters :-))
> 
> Has anyone considered using a high powered OP-AMP such as
> the LM12? It's capable of delievering 10A at 15V output
> swing (on 30V supply).. max power rating of about 80W and
> the data sheet gives schematics for cascading them for
> higher output.. I don't remember if the slew rate is high
> enough for TC frequencies though..
> 
> Ben McMillen

	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.

Ed