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Subject: Re: My transistor blew up...
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NNTP-Posting-Date: Tue, 26 Nov 2002 12:00:58 GMT
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Date: Tue, 26 Nov 2002 12:00:58 GMT
Thank you for the response! Well I just noticed something else. Would it
help at all if I told you that the little hole where it blew was on the
right side of the transistor, where the emitter is? I tried two different
transistors (one that I did now know the ratings... stupid me) with the same
result, only the second one blew instantly and considerably more violently
(it was the one I didn't know about). Thanks again for the help,
"Ban" wrote in message
> Jordan wrote:
> > Hello everyone,
> > I had a flyback transformer driven by a single transistor
> > circuit, which was working fine, but then out of nowhere my
> > transistor blew up. I was using an MJE13009, NPN power transistor
> > rated for 400V at 12A. It was heatsinked and all, wasn't even getting
> > hot. So I thought to myself... if I took two transistors that were
> > exactly the same and wired them up in parallel, would that split the
> > current to both transistors to switch separately and equally? BTW the
> > circuit I was using came from here:
> > (http://www.angelfire.com/80s/sixmhz/flyback.html) Sorry for my
> > ignorance, I don't know much about electronics in general Thanks for
> > all your help!!
> That guy of the webpage doesn't have any idea how this circuit functions,
> impressing the list of various transistors he "fried" already.
> It is more of a miracle this circuit works at all. There are 3 basic
> flaws, each leading to either immediate or gradual destruction of the
> first and worst:
> you just need to miss one single base current pulse and the primary
> will be only limited by the lead resistance to the battery. If there is a
> short on the high voltage side is enough.
> The transformer saturates...
> just put a 0.47R/10W resistor in line with a 2A fastblow fuse into the +
> line to the 12V battery. If you have a higher battery voltage, the
> should be (Ubat - 9V)/5A
> 2. The collector voltage of the transistor rises until a current flows on
> the high voltage side.
> Across the primary coil has to be one or two zener diodes 150V/5W in
> with a normal diode (fast 400V/2A). All rings have to point away from the
> collector side. The zener voltage should be below the max. repetetive
> collector voltage.
> Another fast diode across the emitter and collector with the ring to the
> 3. also the base voltage can become too negative, this probably has
> your transistor.
> a 1n4148 from gnd to base. Ring to base.
> A 0.1uF from the 12V coil-in to gnd.
> Better would be a current steered design with a comparator instead of that
> extra winding on the transformer.
> ciao Ban
> electronic hardware designer
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