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Problems with 555 Flyback Driver and Flyback Driver Discussion

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flannelhead

Sat Jul 05 2008, 12:39PM

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

But still, there are many newbies around here, who don't like to start with several hundreds of watts, but like to start their experiments with lower powers.

There are generally two options for a low power flyback driver, the 2n3055 driver, and the 555 one. Some beginners choose the 555 circuit because they want to audiomodulate it later. Now you would ask, why not to use SG3525 or TL494 then. The answer is that they aren't available in some places.

Those were some points from the view of a beginner, which I still think I am.

Marko

Sat Jul 05 2008, 04:30PM

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

But still, there are many newbies around here, who don't like to start with several hundreds of watts, but like to start their experiments with lower powers.

Well, nobody is preventing you from running Mazzilli or halfbridge circuit at much less than several hundred watts.
Hints: lower supply voltage, higher number of primary turns, reduction of duty cycle of PWM controllers.

I'm sure TL494 is nearly available anywhere NE555 is, and SG3525 very likely too. Look inside computer power supplies for TL494.

Nothing makes one topology ''more powerful'' than another, although there are those that do work and are widely used because of that, and those that don't! :P

Marko

Antonio

Sat Jul 05 2008, 05:03PM

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

It's possible to include current limitation in a 555 driver. A transistor senses the drain current and lowers the duty clycle by draining current from the capacitor connected to pin 5. This is a simulation on the Switchercad III simulator. I didn't try it yet in practice, but the simulation works perfectly.

Update: I made a test. The circuit works correctly. I used an IRF630 mosfet and the regular input winding of a monitor flyback transformer, powered with 24 V. This produces 5 mm arcs, as the transistor clamps the voltage over it at 200 V. With an external winding, greater power could be obtained. 1 Ohm at the source limits the current at about 1 A. 0.5 Ohms at 2 A, and so on. The output can be safely short-circuited.

Firefox

Sun Jul 06 2008, 12:26AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

I'll give that a try, Antonio, since I already have the circuit built. Then I'll report back here.

Dr. SSTC

Sun Jul 06 2008, 01:53AM

Registered Member #1407 Joined: Fri Mar 21 2008, 07:09AM
Location:
Posts: 222

Dr. Conner wrote ...

I agree with everything Marko and Richie said, flyback drivers are for kids :P

Well you got to start somewhere

TheBoozer

Sun Jul 06 2008, 11:52AM

Registered Member #1535 Joined: Wed Jun 11 2008, 11:37PM
Location: Northeastern Pennsylvania - USA
Posts: 117

"Flyback drivers are for kids" reminds me of a TV commerial. Though I don't watch TV anymore because I took the flyback out and it doesn't work now. The little transformer has provided me with many more hours of entertainment than any amount of reruns could... :)

My last project was a flyback driven jacob's ladder. My recipe was an AtTiny26 with an HCNW3120 optoisolator. In the end I used voltage feedback to maintain a constant current supply to the flyback. It's a convenient microcontroller for the project I chose. The Uc has seven readily available ADC pins. One timer was used for PWM drive. Another timer was to modulate the output. Although the whisper silent jacob's ladder was pretty neat too...

Adding feedback boosted my performance, decreased component temperatures. No amount of fine tuning a manual squarewave (like a 555 output) worked for me. (I like the 555 circuit with feedback up there)

Here's a sample:

]inthetube.mpg[/file]

quicksilver

Sun Jul 06 2008, 03:21PM

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

Dr. Conner wrote ...

,...flyback drivers are for kids :P.

And that's why they are so much fun

But I personally have never used a 555 driver in a flyback as (for the reasons Marko pointed out: it is not a "flexible enough switch") it didn't make sense within the component design. But using one in a automotive coil to draw arcs appears to make sense as it substitutes for the mechanical action that the coil was designed for. The Mazilli driver and related concepts have stood up to enormous abuse (with flyback arcs) from this Beginner.

When learning a new hobby I always attempt to chuck my ego and listen to logic; the switching element of the 555 simply doesn't appear warranted in the flyback-arc-drawing phenomenon. I once made a little switching circuit for another project and after blowing out a component the 3rd time, I KNEW that either I had been either sloppy, unprofessional & absent minded or the circuit was junk. I found (much to my chagrin) that the circuit was garbage. Just because it was posted on the internet didn't make it a worthwhile design.

I can understand my own blundering but when I chase a design that is error filled from the start: it's really annoying. That's why I am wary of first versions of software releases!

Dr. Dark Current

Sun Jul 06 2008, 06:25PM

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

I'm sorry, I didn't take time to read the thread all the way.

Marko wrote ...

- Ignore Jan Martis, his site, and all the schematics of ''NE555 flyback drivers'', never build them. And I'm saying that solely because I'm evil. ( :D )

Marko, with the quasi-resonant driver I have gotten 200-300 watts of (real) input power with single or "double" (paralleled) IRFP250 switch. The output voltage from the transformer is respectable (I think I had it at 80kV+, arcs initiating at 13cm between two nails) and if you use the right resonant capacitor, the power is renturned to filter capacitor and power draw is low with output shorted!

Here is the quasi-resonant driver in action (ignore the voltages I think they are wrong)

(Sony Trinitron flyback, I had it do more later. Notice the small heatsink, gets just barely warm)

(first attempts, crappy DC transformer found in every other TV)

And here is a schematic that should work for most:

Read the notes. I had good experience with including secondary current feedback to maintain constant secondary current by limiting duty cycle, after this mod the circuit is nearly indestructible.
As the driver does not create such big negative spikes on secondary as half-bridge type drivers do, it can be obtained more output voltage from the transformer before the diodes break down.

Marko, I don't know all the theory like you do, but this topology has worked extremely well for me in practice. This circuit is built from experience and experimenting with various lash-ups. You can say what you want, it does and will work well for me.

-J.M.

Firefox

Mon Jul 07 2008, 02:21AM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

Thats pretty incredible Jan, I have a bunch of salvaged 200-400V 5-30A MOSFETs to try this out with. To the workbench!
Also, I'm going to expand the scope of this thread due to the incredible amount of info presented here, I believe this is a discussion that can be found piecemeal throughout the forums, but I've never seen so much information at one spot. I might even be motivated to compile it into HVWiki format for posterity.

Marko

Tue Jul 08 2008, 09:09AM

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

Jan, I've been silently watching your work for a while and was always impressed. Quasi-resonant topology is still great advance from circuit shown in the first post, which is what we were specially referring to - it is spread all over internet and apparently most newcomers see it as something great, which I wanted to debunk.

I just want to end the endless cycling of the 'NE555 flyback driver' (not quasi resonant or with any sort of current control) around the internet which always ends with frustration for most people and is not fruitful.

Pulse-by pulse current limiting is great improvement to, and it is neither included in the circuit shown in the first post!

Jan, did you use current feedback when running at 300W? I would expect heavy loading and especially short circuit of the output to result in dead switches or very poor efficiency in all cases without some means of current control and preventing saturation.

And why did you use two paralleled switches? For efficiently working circuit and just 300W I would expect one IRFP250 to be just fine.

I have offered an explanation why might the circuit ''just work'' without current control, because of negative resistance of the arc ''balancing out'' Vs as output current drops, but saturation still needs to occur in order for that to happen, and high current surges would flow in the switches bo matter what is done.

Marko, I don't know all the theory like you do, but this topology has worked extremely well for me in practice. This circuit is built from experience and experimenting with various lash-ups. You can say what you want, it does and will work well for me.

Well, if theory and practice don't match, something is wrong wither with theory or experiment...

Most of this, more or less, comes from Richie's head anyway, but it did make sense to me (I may be though one of those who got greatly frustrated with 'ne555' circuit in past and lost objectivity :P )

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