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Blew a hole through a 2n3055

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dan

Mon Jul 10 2006, 07:20PM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

You guys probably arn't going to belive this but I was running the classic daul 2n3055 push pull flyback driver and at some 40v input, and then BANG. (no, the fact that it failed isn't the unbelivable part.. Please read on.).. Most of the time when these transistors fail you only hear a small pop and then the driver quits. However this time there was a noticeble BANG and on further inspection there was a hole burned through the 2n3055 case. The power supply was a 20A variac with a rectified & filtered output(0.1F filter capacitor). This was the first transistor faliure with this Power supply and stupid me I didn't incoperate any current limiting in case of such a failure so it also managed to jump the 20A breaker to my lab(aka: room). I also blew the 40A rectifer bridge and the flyback is dead now too (easy come easy go I guess). Luckally I didn't toast my precious variac. oh well enough with the story here's the pic..

P.S. Sorry I haven't been around the forum lately.. just been busy working at crappy tire(Canadian Tire)

Marko

Mon Jul 10 2006, 08:00PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

'3055s have metal 'pins' inside the case wich connect leads to silicon die.
Blowing die may have sent them off causing one to remain shorted with case.

For the driver I think it's better to invest in 2 mosfets rather than '3055s and build yourself a mazzili driver.

dan

Mon Jul 10 2006, 08:15PM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

Yeah i know the 2n3055 driver is horrible but I really can't resist the simplicity of it.. but obvouisly these 2n3055 have their limits. It's just I have never heard of a TO-3 package transisitor failing this spactacularly. These little cans are really tough and to see a hole blown in one in rather suprising to me. (one in a million I guess) Too bad it didn't blow the top clean off

Marko

Mon Jul 10 2006, 09:10PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

It really can't any simpler than mazzili driver. And even gets cheaper after just 2-3 blown '3055s.

And it showed to be one of really best drivers in the end

Dr. Dark Current

Mon Jul 10 2006, 09:12PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

dan wrote ...

... and at some 40v input, and then BANG. ... The power supply was a 20A variac with a rectified & filtered output(0.1F filter capacitor). ...

guess where those 80 joules went......

Avalanche

Mon Jul 10 2006, 10:10PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Now that's a blown transistor where you can say "I bet I couldn't do that again"

I would have been quite amused if that happened to me, usually mine just fail with no sign at all.

Marko

Mon Jul 10 2006, 10:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I guess TDU can do it again (and blow the top can off too) with some of his caps.

I also think that this is pretty rare for TO3 since silicon die usually vaporizes first opening the circuit and can leaves it enough room to blow without ripping the device apart.

That hole looks most like it is a result of metal pin or something from inside contacting the case (and lots of energy discharging trough it afterwards).

dan

Mon Jul 10 2006, 10:30PM

Registered Member #223 Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125

Yeah it was probably a one in a million shot.. but it was rather interesting loss. Also one thing I noticed is that if I tilt it the right way some white powder comes out of it. probably the burned sillicon.

I have about 8 2n3055's left. Since they are pretty much useless and dirt cheap I was thinking about destroying a few.. My goal would be to blow the cover clean off. I'm thinking about charging my 500V 1.2kJ cap bank and discharging it accross the B-C connections. I'm betting that would blow it off.

I have heard about people cutting the cover off with a hack saw which then converts it to a phototransistor. Not sure how useful this makeshift phototransitor would be but probably another "interesting" project to try. Maybe put some clear epoxy over the die to protect it.

Marko

Mon Jul 10 2006, 11:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

You can use a LED as (poor but usable) photodiode in reverse without any mod's.

2N3055 would be just about useless than for a show.

It could aslo be used to prduce weak light

Simon

Tue Jul 11 2006, 12:29AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

dan wrote ...

Yeah it was probably a one in a million shot.. but it was rather interesting loss. Also one thing I noticed is that if I tilt it the right way some white powder comes out of it. probably the burned sillicon.

It's best to be wary of powders that come from power transistors. Many contain berylium oxide. Nasty stuff.

Edit: Yeah, I know it isn't likely to be a problem here. I just thought I'd point it out. That's why I wrote "best to be wary" instead of "OMG! Teh BeO!!!"

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