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

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

2N3055's should be $0.50 each. but they are a terrible choice to drive
anything with HV in it.  Why? because they have a 60Volt BVceo (thats
breakdown voltage Collector to emitter).  Sure, folks run them, mostly
because the breakdown is energy limited by other components so the power
dissipated is low enough to prevent cooking them. However, they WILL die
eventually.  A much better choice would be a Horizontal Output Transistor
(radio shack used to have them, they may still), or a transistor made for
electronic ignitions (450-700 V BVceo and 5-10 A Ic max)  that has a
several hundred volt BVceo. Both of these are made in enormous (millions)
quantities so they should be cheap.

However, if you insist on running a 3055.... Try putting a neon bulb across
the collector and emitter. It acts like a 60-70 volt limiter to clip the
spikes.  If you blow up the neon bulb, you know you've got some other
problems.  Or, the solution used in electronic ignitions (a very similar
application, if you think about it) is a 450Volt Zener. Take a look at the
data sheet for the Motorola MC3335 (I think), automotive electronic
ignition IC for ideas.

2N3055's are ubiquitous, but they are basically a low voltage (60V) low
gain (hFE of 15!) low frequency (fT of a few hundred kHz)  part for things
like linear DC regulators.  Lots of people have a box full of them that
they picked up somewhere (myself included), and so when they need a power
transistor to try something out, they use it.  There are a lot of better
parts that are just as cheap (surplus and new)... 

Think of applications that are mass, mass market: consumer/automotive/etc.,
and look for parts that would be used in that, and hunt those down.
.
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> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: The ignition coil driver circuit again!!!!
> Date: Saturday, September 02, 2000 12:25 PM
> 
> Original poster: "wsc1914" <wsc1914-at-hotmail-dot-com> 
> 
> Well, I have just come across one other problem - the 2N3055 transistor
has
> just burned out. I'm not sure if this was the heat or it was a power
surge.
> Whenever I try to use it now it buzzes quietly (like normal), but it gets
VERY
> hot VERY quickly, and no power comes out of the coil.
>  
> I thought about putting a cap over the transistor Collector and Emitter
to
> supress surges. I have the following - could someone tell me what would
be
> suitable, if any of them?
>  
> 10000uF 16v Electrolytic
> 220uF 35V Electrolytic
> 0.1uF 50v Ceramic (I don't think so!)
>  
> Any ideas?
> Please reply quickly if you have the time - as I want to get this working
> properly before I burn out any more! They are not cheap!
>  
> Many thanks to all!
> Oliver.
> 
> 
>