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Transistors & Flybacks

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quicksilver

Sat Apr 05 2008, 06:05PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I have been reading quite a bit of commentary on high power transistors in flyback circuits. Often web page writers comment that the newer flybacks are sensitive to the transistor. Rather than the newer flybacks not working as well as older designs; it's often stated that the common 2N3055 is just not up to the task.
On several occasions I've read that the 2N3773, NTG285, MJ2955,& MJE13009 are the way to go as they have stronger operating parameters. This seems logical and I don't want to re-invent the wheel. My question is this: I have several 2N3055's; could i run them in parallel for greater performance? And would that be an option?

If I have to I would go into town and buy new ones but it seems a shame. What have been some of the results of those with experience in-so-far as using any of these transistors with the newer flybacks?

Dr. Dark Current

Sat Apr 05 2008, 07:00PM

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

quicksilver wrote ...

If I have to I would go into town and buy new ones but it seems a shame. What have been some of the results of those with experience in-so-far as using any of these transistors with the newer flybacks?

If you go to town, buy a 555 and a MOSFET (IRF640/IRFP250 or similar). Seriously, the "single transistor driver" converts more power to heat than the arc.

If you really want to use your driver: Always wind your own windings on the flyback (use a bit more turns for the primary, 6-8 seems to work well and keeps the transistor cooler). This way you can drive any transformer, the newer ones just as well as the old type. Polarity of the windings is important with the rectified types.

I have an improved circuit for the single transistor driver, if you want, just ask I have a thread somewhere.

quicksilver

Sun Apr 06 2008, 12:15AM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I am VERY interested! This is exactly what I am looking for. -=Please post this=-

I have spent some time today de-soldering several old monitors to obtain quite a few flybacks in the hopes of finding a simple disk coil (older) flyback. No luck, even with monochrome but I wound up with quite a collection of parts for many experiments!

I even opened an old TV that I thought MAY have a toroid coil.... but IF I could use a modern flyback - I'm set!

What I am trying to find as well is some method of recognition of the MOSSETs, etc that I come across to identify them.

Frankly, I am covinced that the hobby of HV experimentation will become much more difficult to participate in as the world is moving to greater energy conservation in the engineering / design modality of modern electrical devices. I am hoping to continue to collect material for this hobby as I believe it will become much harder to find.

techniques like using semi-modern flybacks will become invaluable as the old toroid flybacks will become almost impossible to collect. I have seen more and more neon sign transformers shift from the useful designs to ones strictly manufactured for energy conservation...

Check out the designs commonly sold today:

Ultra7

Sun Apr 06 2008, 03:56AM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

I know where to find old disk style flybacks for CHEEEEEP!
Logan Kennedy has some for sale in the "Sale and trade" category.
I found his source, so I picked up 2 for me.
But I bet he still has some in his garage.

Backyard Skunkworks

Sun Apr 06 2008, 04:48AM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

I've never really dealt with flybacks before, so this may be kind of a stupid question but...

Is it impossible/very hard to make your own flyback transformer?

Is this just a matter of poor efficiency or is making your own flyback totally futile?

Andyman

Sun Apr 06 2008, 06:33AM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

Besides having to wind several thousands of turns of wire that's several times thinner than human hair and will break with the slightest tension, and providing sufficient insulation between layers, they should be relatively easy to wind.

Seriously, its not worth the trouble for the average hobbyist.

flannelhead

Sun Apr 06 2008, 06:44AM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Actually you don't have to wind thousands of turns. Check this:

I would call those arcs very impressive from a self-wound flyback. And the winding takes only 5 minutes.

Dr. Dark Current

Sun Apr 06 2008, 07:09AM

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

quicksilver wrote ...

I am VERY interested! This is exactly what I am looking for. -=Please post this=-

Use smaller capacitor across the transistor, 0.22uF to 0.33uF, 400V (230V~) often works best (by now you should have enough of these from your old monitors

)

Edit- I forgot, of course you have to use an air gap in the flyback core

Backyard Skunkworks wrote ...

Is it impossible/very hard to make your own flyback transformer?

It's not impossible, it is perfectly doable. Around 1000 turns is enough if you are using any usable driver (zvs, bridge...). Just wind 50 turns, insulate with transparency foil (the "hard" type that comes in A3/ A4 formats), wind another 50 turns... until you are done.

Antonio

Sun Apr 06 2008, 01:41PM

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

If you are disassembling monitors, take out also the power transistors that connect to the flyback, and the high-speed, high-voltage diode in parallel with the transistor. You may need also the high-voltage capacitor that acts as snubber. Look at the board and you will probably also find medium power mosfets. Actually, everything is useful, even connectors, cables and screws.

quicksilver

Sun Apr 06 2008, 02:27PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Antonio wrote ...

If you are disassembling monitors, take out also the power transistors that connect to the flyback, and the high-speed, high-voltage diode in parallel with the transistor. You may need also the high-voltage capacitor that acts as snubber. Look at the board and you will probably also find medium power mosfets. Actually, everything is useful, even connectors, cables and screws.

I was very surprised that there was SO MUCH useful stuff in there. You are absolutely correct! In some monitors there are excellent MOSFETs, heat sinks, all sorts of things that are actually rather expensive if I bought them. All very useful.

This brings me back to my second query......Identification of semi-conductors, etc. MOSFETs, diodes, & assorted goodies are often difficult to decipher as codes are altered from manufacturer to manufacturer.... With the use of flat screens on the majority of desktops now, the old CRT monitors will be a treasure trove of parts for a year or so until they all disappear. I wish there was a simple method to identify some of those parts aside from going to the various manufacturer's web sites and writing down all their codes to ascertain which code type was used, etc. If I could even find one item technique (other than obvious resisters) like diodes; that would be a real boon.

Plasmaddict wrote ...

Edit- I forgot, of course you have to use an air gap in the flyback core

Do you have an example of a "core air gap"? Maybe I'm just being stupid on this but the term "core" is what I'm stuck on... thanks.

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