If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Note that this circuit is not thoroughly tested, any ideas for improvement or succesful replications are welcome
I was messing with the self-oscillating circuit from the CFL and thinking ways to improve it to be efficient enough to drive flybacks. Among my ideas was a circuit which provided a voltage output for the bases rather than current, and I thought, MOSFETs are voltage driven so why not try it?
And it worked! After some tuning it works nearly as efficiently as any other halfbridge (drawing 3" hot arcs and the little FETs remaining at room temp for short runs), requiring only very few components. Apart from the start-up circuit and the essential components, there are only 2 other components - a little transformer and a resistor.
Note that it sometimes gets messed up with secondary open circuit, I think that is when the circuit happens to oscillate near the transformer's resonant frequency, sometimes I noticed it even tries to tune into resonance (and I have no explanation for that), which is of course destructive for both the transformer and the bridge. Other times it runs perfectly fine with open output.
However, if you don't let the output go open circuit such as when powering a Jacob's ladder, it works beautifully.
How does it work? It is based on the fact that the GDT saturates sooner than the main transformer, switching off one of the FETs, at which point the primary voltage "free-wheels" to the other polarity and the other FET is switched on. The saturation volt-seconds for the GDT is the main factor in determining the running frequency.
I think it could as well be used for super-simple SMPS's (without regulation)
Forgot to clarify, the GDT is wound on a ferrite ring. (I hope the phasing is right)
Edit: my GDT has a cross-section of around 50mm^2 if that helps anyone. Maybe a little bigger could be better, or add a turn or two on a small core to bring the frequency down.
Edit2: It seems to work even without the resistor between the feedback and GDT. It is though not recommended to let the output go open circuit
Registered Member #127
Joined: Fri Feb 10 2006, 03:36PM
Location: Cincinnati, OH - USA
Posts: 44
That is quite elegant. What is the breakdown voltage of your DIAC? And what are the specs of the FETs you are using? And the caps between the transformer primary and supply? I was thinking of trying to replicate this so if this information should somehow be obvious, let me know and I will do some searching on other designs. Thanks a bunch!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi, the breakdown voltage does not matter much, but should be above some 25V.
The caps are standard PSU electrolytics, like from a PC PSU, something like 220-680uF on 200 volts.
Use FETs you would use for any other half-bridge, IRF740's work well up to moderate powers (~200-300W), or IRFP460 for higher powers.
I have improved the design since - I've replaced the 12ohm resistor with a little inductor, mine consists of 15 turns of 1mm dia wire on a 15mm form, air core. But it should work with the resistor too, it just wastes power a bit.
I suggest to put some lightbulb in series with the mains while testing, so you don't explode your FETs on first turn-on :)
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Harry wrote ...
What is fo, son?
You mean running frequency? As i said in my first post, it is determined by the saturation of the GDT core, how many volt-seconds it can take. To lower the frequency, add turns on GDT, similarly to raise the frequency, remove turns.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Dr. Kilovolt's super simple, self-oscillating MOSFET halfbridge flyback driver
