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2N3055 Flyback Driver

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Michael W.

Fri May 19 2006, 11:52PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I've tried this twice and both times the transistor was killed without arcs being made (rectified monitor flyback)..

Following somthing relative to this site...

(circuit only, not the same transformer)
Any suggestions or replacment ideas?

Hazmatt_(The Underdog)

Fri May 19 2006, 11:56PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

You have to follow a basic rule first. With a split core it has to be driven externally, when the core is closed then you can drive it self resonant.

So remove gaps first then try again. The next step is to optimize the resistance to the bases, since they get pretty darn hot.

cbfull

Sat May 20 2006, 01:35AM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

Yes, base resistance is important, but the value is not crucial. Just make sure it's about 30 Ohms or more. I don't know this for a fact, just some experiences. Normally I would go with about 20 Ohms, but those Radio Shack transistors are so damn unpredictable, high base resistance might help to keep them from saturating and/or dying. Honestly, I don't know for sure why they die, it's just a suggestion.

I have always purchased transistors from electronics companies which is WELL worth it as far as quality goes, and they don't cost that much if you just order enough to meet their minimum order. Ebay is good route, but there is a possibility that you could end up with counterfeit transistors, and I have some to prove it, believe it or not.

I also agree about the gap spacers. I read some stuff when I built my first circuit that said to never lose the spacers because they are crucial, but I later realized that it is only crucial if you are replacing one for a CRT. For straight HV transformer use, get rid of the gap. When I closed the airgaps in my circuit, the efficiency improved noticably and the transistors didn't heat nearly as fast, not to mention the output improved. The only drawback I noticed was a frequency drop into audio-ish range. It kinda started screaming a little.

There is a way however, to fix the frequency of your circuit to avoid this type of situation, without using a 555 or another chip. The method involves placing another ferrite transformer with a center tapped seconday to supply the bases of the transistors. The second transformer needs to have a lower saturation than the first to make sure you never allow the output transformer to saturate. This will shut off the bases before the main transformer saturates, and the frequency will remain much more stable no matter what the load. I don't know EXACTLY how this will work on these circuits because I have not tried it yet, but it is a VERY interesting idea.

If anyone is interested in this, let me know and I'll try to find a link to the circuit (I might have to dig).

Hope this helps!

Dr. Dark Current

Sat May 20 2006, 07:36AM

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

ForceLabs wrote ...

I've tried this twice and both times the transistor was killed without arcs being made (rectified monitor flyback)..

Following somthing relative to this site...

(circuit only, not the same transformer)
Any suggestions or replacment ideas?

For driving a new-type DC potted flyback,
-Use the internal primary (0.5 - 1 Ohm),
-Substitue the 3055 for a HOT (Horizontal Output Transistor), [get it from the same monitor]
-Wind 5-10 turns external feedback winding on the exposed core,
-Supply it with more volts (40V is usually enough), it will need just little power (10-20W).
-(you can change the resistors for a higher ohms ones, just preserve the resistance ratio)

If it doesn't work, try all possible (4) combinations of polarity of all coils.
With this driver, It is easy to make 5cm sparks, just what your flyback withstands.

Hope this helps, J.M.

Michael W.

Sun May 21 2006, 12:18AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

Correction: I got it working now, It arcs an average of about 3 inches...suprising

Dr. Dark Current

Sun May 21 2006, 05:42AM

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

ForceLabs wrote ...

Correction: I got it working now, It arcs an average of about 3 inches...suprising

Does it start arcs at 3in or draw to 3in? Anyways, this is quite impressive performance with this driver. Did you use the original 2n3055 or better transistor?

J.M.

Simon

Sun May 21 2006, 06:06AM

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

Good to hear you have it working.

I was going to suggest using an MJ10012 if you could get hold of one. BP also uses them. They're darlingtons with ample current and voltage ratings (something like 600V, 10A from memory). Much better than the 2N3055 and can be driven directly from a 555.

ragnar

Sun May 21 2006, 07:23AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Ya, I've had some really nice experiences with the MJ10012... I did use an intermediate BC327 between it and the 555 though...

Michael W.

Sun May 21 2006, 02:11PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

It arcs at three inches and if I draw it any longer theres just a ton of corona....

Michael W.

Tue Aug 01 2006, 04:43PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

ooo...digging up an old thread. My flyback driver listed above worked beautifully until I pushed it too far and one of the resistors exploded, apparently killing the 2n3055. After replacing the resistors with larger 5-10 watt ones, now the whole assembly won't work. I'm not sure what makes a dead 2n3055 (pin continuity) but its not doing anything now. Suggestions?

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