Re: The ignition coil driver circuit again!!!!

["Luc" <ludev-at-videotron.ca> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi

I remember seeing a plan but I can't find it anymore they use a diode 1000V 3A
in Seri with a ceramic cap .i mF 3KV in parallel with the ignition coil.

Luc Benard

Tesla list wrote:

> Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
>
> Exceeding the max Collector to Emitter voltage when cutoff (BVceo in the
> data sheet).. 2n3055 is rated at 60V, and probably will do 70-80 volts
> depending on temperature and which mfr lot you got.  What happens when you
> exceed this is that the transistor starts to conduct (much like a zener),
> except worse, because it can cause the base to become forward biased which
> can turn the transistor partly on.   In any case, big voltage across
> transistor + current flowing means lots of power dissipation, which will
> melt it in short order.  This is especially true if part of the transistor
> breaks down first (as it will), so the heat is concentrated on the die.
>
> There ARE transistors designed to have a "good" breakdown characteristic
> (i.e. they don't self destruct, given suitable external energy limiting).
> They are used in things like electronic ignitions driving, of all things,
> ignition coils.  The typical ignition circuit sees 300-400V or so when the
> transistor turns off (making the spark). Typically, the spark in the
> cylinder actually limits the voltage, when it starts to conduct. However,
> if the sparkplug misfires, or the lead falls off, or the transistor turns
> off more quickly than planned (high di/dt), then the voltage can go higher.
>
>
> You could just specifiy a 700-800Volt transistor (like used in TV
> horizontal output apps). But,  HV transistors cost more to make than low
> voltage, and automotive apps are very very cost sensitive (pennies count:
> If you make 10 million ignitions a year (which they do), you can afford to
> have an engineer spend a year ($200K) figuring out how to reduce the cost
> by $0.02), so the solution is to specify a 400V transistor, with good
> avalanche characteristics to handle the few times the voltage spikes
> higher.  Most transistors can take some abuse before catastrophically
> failing....
>
> It is unlikely that you are worried about saving $0.75 on the parts cost of
> a tesla coil, so the moral of the story is to go pay $2 or $3 for a surplus
> transistor that can take the abuse rather It than saving a dollar by using
> the 2N3055.  If you need one CHEAP, (like free), find a dead TV set and
> scavenge the horizontal output transistor.
>
> ----------
> > From: Tesla list <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: The ignition coil driver circuit again!!!!
> > Date: Sunday, September 03, 2000 3:16 PM
> >
> > Original poster: "wsc1914" <wsc1914-at-hotmail-dot-com>
> >
> > What do you mean by breakdown?
> >
> > ----- Original Message -----
> > From: Tesla list <tesla-at-pupman-dot-com>
> > To: <tesla-at-pupman-dot-com>
> > Sent: Sunday, September 03, 2000 6:49 PM
> > Subject: Re: The ignition coil driver circuit again!!!!
> >
> >
> > > Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
> > >
> > > The problem is probably breakdown, not over current.  The 2N3055 can
> take
> > > 15 Amps all day long and, on a good heat sink, can dissipate 150W.
> > >
> > > ----------
> > > > From: Tesla list <tesla-at-pupman-dot-com>
> > > > To: tesla-at-pupman-dot-com
> > > > Subject: Re: The ignition coil driver circuit again!!!!
> > > > Date: Saturday, September 02, 2000 4:20 PM
> > > >
> > > > Original poster: "wsc1914" <wsc1914-at-hotmail-dot-com>
> > > >
> > > > Do you think it would take the strain off the2N3055 transistor if 2
> of
> > > them
> > > > were put in parallel, then the current would the shared between them.
> > > >
> > > > Oliver.
> > > >
> > > > ----- Original Message -----
> > > > From: Tesla list <tesla-at-pupman-dot-com>
> > > > To: <tesla-at-pupman-dot-com>
> > > > Sent: Saturday, September 02, 2000 10:22 PM
> > msnip...
> >
> >