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Parallel 2n3055 Driver

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aonomus

Mon Jul 21 2008, 01:52AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Ok, well since I got my digikey shipment I've been busy, I made a flyback driver using 2n3055's which doesn't seem to do squat.

What I've done is bolted 2 2n3055's onto a heatsink and paralleled both together, I've tried everything that I can do to get this to work. I've tried reversing the direction of windings, reversing winding connections, even swapping out the transistor to one that worked with a previous driver. The only variable that I haven't covered from previous experiments would be a extra metal poly 1uF cap that I had across my PSU output to filter any ripples.

The only thing that I'm suspicious of are the windings on the flyback being too loose, would using 14AWG wire which can't form a very tight turn at the corners of the core cause nothing to work? I've tired pushing up to 30V at 3A with part of the power just going through the resistors, nothing has happened, and the feedback coil shows no response on an oscilloscope.

Or it could be a stupid mistake, can anyone confirm that 2n3055's pinout follows this:

I'm lost as what to do now, any thoughts?

Plasmaarc452

Mon Jul 21 2008, 03:08AM

Registered Member #1394 Joined: Sun Mar 16 2008, 06:18PM
Location:
Posts: 111

Thats the pinout, the 2n3055 is worthless if your using a single transistor driver. It burns out very easily.

Other than that I can't really help you, I have never tried using 2 transistors together.

aonomus

Mon Jul 21 2008, 03:19AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I finally got it, I had the feedback coil wired up in reverse, I remembered that the feedback coil by default turns the transistor on, and when the primary turns on, the field cancels out the feedback coil. The two coils had to be wired up antiparallel as a odd way of describing it.

Edit: further tinkering has yielded long 1-1.5inch dim arcs, and the transistors barely heat up at 30V 5A, however after 10-30 seconds the transistors heat up too much and the heatsink needs more time to absorb the power.

Its my first actual fly back driver, my first attempt was with a TIP122 darlington transistors, once I move back into my apartment and I'm back with my drill press I'll be getting a bigger heatsink to mount TO-3P packaged FJA13009TU transistors which apparently work much better.

aonomus

Mon Jul 21 2008, 05:11AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I did a long writeup of the project on my blog, so here's the pictureless excerpt (I can't figure out how to use the img tag to resize externally hosted images, and my images stretch the forum, so you'll just have to go here).

The abstract of the project is that I paralleled 2 2n3055's and managed to put 30V at 5A into the driver with no significant heating unless the arc was short and hot, which caused the transistors to heat up faster than heat could transfer to the heatsink. My next step is to build a push-pull configuration using an identical bank for the second transistor.

To the mods: sorry if linking to my blog isn't explicitly allowed, if it isn't I'll insert the pictures and rewrite the post. Or alternatively if you know how to use an img tag to resize an image that is externally hosted, lemme know!

So for my first real flyback driver, I built a dual 2n3055 transistor based flyback driver. The gist of it is that while one 2n3055 overheats very quickly, 2 paralleled 2n3055s will be able to split the current load and avoid overheating too rapidly.

I used a long terminal strip to arrange the resistor components, had a fan on the heatsink to cool it down, and used some alligator clip leads to make a chicken stick for the HV side.

Once I had the driver setup I was able to push up to 30V at 3-4A into the driver with only moderate heating of the transistors. Short hot arcs or long-duration arcs cause the transistors to heat up significantly, and a short cooldown time is required for the heat to transfer over to the heatsink where it is quickly dissipated. After I figured this out, I was able to push up to 5A (max capabilities of my PSU), where arc over of the flyback pins started to occur, melting charring one of the alligator clip insulating boots slightly.

After I solved the arcover problem with some extra plastic insulation, the fun began, I strung together 3, then 4 disposable camera flash tubes. When you connect a flash tube directly to the flyback, it has a dim arc inside the tube, but I suppose the slight capacitance of the wiring creates a much brighter flash whenever a momentary arc forms.

Another interesting discovery I made was that at these voltages, everything behaves differently, particularly electrostatic attraction/repulsion, and magnetism. At HV, tissue paper flies away from the negative lead, and camera flash tubes roll away, youâ€™ll have noticed that I had to tape down the tubes earlier because they continued to roll away.

The schematic (source: wiki.4hv.org) of the driver is fairly straightforward, the only issue I had was remembering that the feedback coil had to be reversed. The basis for this circuit is that there is always current flowing into the base of the 2n3055, and that when the primary coil energizes, the magnetic field of the transformer core cancels out the voltage in the feedback coil, turning off the transistor, which allows the feedback coil to come back up to voltage, and the cycle repeats. A similar driver exists where 2 2n3055â€™s are set in a push-pull configuration for full-wave AC input, which is my next step, followed by a Mazilli ZVS driver with IRFP250â€™s. Until then, this driver should be useful, right up until I burn out the secondary that is :D

Arcstarter

Mon Jul 21 2008, 05:19AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well, if you want the transistor to dissipate heat to the heatsink better, just buy some heatsink compound or wth ever it is called

. You can get it from radiosh$#(thanks for that Dr. Connor

) but you know how they overprice everything.

Plasmaarc452

Mon Jul 21 2008, 05:31AM

Registered Member #1394 Joined: Sun Mar 16 2008, 06:18PM
Location:
Posts: 111

I have a very very lame way of cooling transistors without a heat sink, only use this method if you have no other choice.

Get one of those air duster cans, I think they are called dust off. Flip it upside down and point it at the transistor and squeeze the the trigger very slightly so the liquid drips onto the transistor. The liquid is very cold and the transistor will cool while it runs as long as you drip the liquid onto it. Do this every 15-30 seconds while it is running and you don't need a heat sink.

I found this out today while I was trying to charging a 3900uf 450v capacitor. I used a single transistor 2n3055 driver with no heatsink. After about 30 seconds it was getting hot so I said why not try this and after 1 dripping of the liquid the transistor was cold to the touch. About 15 seconds later the frost was gone and then 10 seconds later it started to get hot again. I did this 3 times a minute for 20 minutes without turning off the driver. AMAZING!!!!! The power supply that I used was hotter than the transistor lol!

aonomus

Mon Jul 21 2008, 05:42AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

If you look at the picture (here), you'll see that there is that annoying white thermal grease . I torqued down the nuts pretty hard, so its a transient heat spike which goes away within about 5-10 seconds, but should always be kept in check. Heat transfer efficiency obviously decreases as the temperature of the heatsink increases (thus, the deltaT between heatsink and transistors decrease).

As for the duster cans, thats an expensive way which doesn't last too long, and the heat shock of -20-30 degC against the transistor can't be good for it. They sell 'freeze' sprays which are basically a duster can with a dip tube, duster cans take the gas, where freeze sprays take the liquid. I've gotten frostbite trying this before too freezing down a MOSFET in an overheating audio amp, and during the thaw process, water must have condensed and mixed with the dirt creating a short, frying the mosfets which were paralleled.

Edit: I wonder what would happen if I paralleled 4 of these things.... :D

Dr. Dark Current

Mon Jul 21 2008, 06:30AM

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

I had good experience paralelling transistors in this driver, they don't heat up as fast and you get more power. And as in any similar thread I'll link this

while you're at it. It improves performance in most cases and in some cases it improves it quite dramatically

aonomus

Mon Jul 21 2008, 06:57AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I tried modifying my circuit with the protective diode and extra capacitor across the transistor collector/emitter, and it didn't like it. Flyback HV voltage was reduced a fair bit (couldn't arc through as many tubes, arc length reduced), and the capacitor got darned hot.

On another note, ST's datasheet for my transistors says max operating junction temp at 200degC, which probably means I could heat my transistors much further than the borderline 'too hot to touch' range at about 40degC?

Antonio

Mon Jul 21 2008, 01:22PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

If the transistors are getting too hot to touch, something is wrong. This kind of driver is really all wrong, without any protection for the transistor. Voltage limitation is trough breakdown of the collector-base junction, and it also breaks the base-emitter junction. A transistor don't support this treatment for long time. A capacitor and a diode across the transistor should improve things a lot, with the right ratings. A capacitor getting hot is something very strange. Probably a wrong kind of capacitor.

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