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Flyback and single transistor driver

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lpfthings

Thu Jul 09 2009, 11:25AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Hey guys, I recently got a flyback out of a 17" CRT monitor and made up a single transistor driver for it. I get arcs, but they are only <1cm at best, and they "fade" out after about 10 seconds of use. After the 10 seconds, the transistor is quite hot.

I have 4 turns on my primary and 3 on my feedback, so can anyone give me some pointers as to why I get such a bad output and the transistor gets hot very quickly? A while ago I had a flyback that could give me ~9cm arcs from this circuit, now I can barely get <1cm (Although it is a newly built one). The only subsitute I made in the circuit is the 240 ohm resistor, which is 220 ohm in my circuit.

Cheers,
Dan :)

Dr. Dark Current

Thu Jul 09 2009, 04:01PM

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

firstly, try swapping BOTH primary and feedback polarities, maybe the flyback pulse is in the wrong polarity.
Then, to increase efficiency, you can try using 5t primary and 2-3t feedback, and decrease the value of the bottom resistor only (this will bring up the power). Use appropriate wattage, it will get hot.

lpfthings

Sat Jul 11 2009, 06:00AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Crap! I used the back end of a soft plastic screwdriver to try and knock the bottom part of the core out, and it snapped :(

It is still only in 2 pieces though, is it possible to just glue them back together with super glue?

Proud Mary

Sat Jul 11 2009, 07:18AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hi Dan, could you say what type of transistor and what voltage you are using?

CompWiz

Sat Jul 11 2009, 07:45AM

Registered Member #1038 Joined: Mon Oct 01 2007, 08:02PM
Location:
Posts: 96

I think it is possible to glue them back together, I think I read it somewhere. And you have nothing to lose trying it, other then a few drops of super glue.

lpfthings

Sat Jul 11 2009, 08:26AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Harry, I am using the 2N3055 as called for in the circuit. I have a bench power supply that can supply 0-16V @ 25A, however I ran it at 12V most of the time, and it only drew about 2A at most. My old flyback on the single transistor driver could give about 9cm arcs on 12V 4A input, so something is wrong.

Proud Mary

Sat Jul 11 2009, 10:14AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

2N3055 is famously tricky in this role. Let me look in my junk box and I'll see if I can find something a bit better for you. I'll send you a PM when I have sorted something out - Harry.

lpfthings

Sat Jul 11 2009, 10:37AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Thanks :)

I found the 555 circuit I tried ages ago, and added the audio modulation to it. Not sure if it'd work or not however ...

555sstc

I can get all the parts for this driver ( Not the transistor specified, but a substitute) from my local electronics shop (Jaycar), however last time I tried it on 12V I got very small arcs. The flyback was from a small B&W TV however, so maybe not a huge performer. The flyback I currently have is like a mini version on my big one that gave ~90cm sparks. The last time I tired that driver, I used a TIP41C, which I soon found out was only rated for 100V, and that it was clamping from the inductive kickback. It did however modulate, but the arc output was pitiful. I guess I need to find a better substitute for the BD243C.

Dr. Dark Current

Sat Jul 11 2009, 11:19AM

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

Have you tried changing the polarity of both primary and feedback coils, like I said in my previous post?

This is very important when driving diode split transformers, because only one polarity will work well (in the other one, the flyback HV pulse will get lost on the diodes and you only get the small forward pulse on the output).

lpfthings

Sat Jul 11 2009, 11:27AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Dr. Kilovolt, I did try reversing them, however my transistor gets extremely hot and the output slowly dies out as it gets hot, so I think the transistor may be too dead for another test.

I do have a transistor from the monitor, but I can't find any specifications on it at all. It's a Panasonic C5914 3D3
EDIT: Found a datasheet for it!

Some pretty big ratings by the looks if it, though is it useable for my purposes?

Cheers,
Dan :)

EDIT: I found a IRF634B in the monitor, seems to have better ratings that the TIP41C, could it be useful for me?

EDIT Again: Seems this Panasonic transistor would work as a direct replacement of the 2N3055, same base voltage, same base current etc. I'll try it out and let you know how it goes :)

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