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 #2656
Joined: Wed Jan 27 2010, 07:12PM
Location:
Posts: 2
I want to build the flyback driver on this website:
But I had a couple of questions first. The most important was which pin is the drain and which is the source on the MOSFETs? I'd assume that the bottom pin on all 4 would be the source but am not 100% sure on this.
Also, out of curiosity, I'd really like to know exactly how this circuit works. I understand the purpose of everything except the diodes and the use of two MOSFETS in series for each output. Could anyone explain what the diodes do and why there are two transistors in parallel?
Registered Member #2655
Joined: Wed Jan 27 2010, 04:09PM
Location: Czech Republic
Posts: 18
If you mean in schematics then yes, the bottom ones are sources. And if I can understand this schematics correctly, this is the full H-bridge schematics. At first, bottom left and top right transistors are ON and the power flows through primary coil in one direction, then they turn OFF and top left and bottom right transistors are turned ON - and the power flows through primary coil in the other direction. Related wikipedia article.
Registered Member #2656
Joined: Wed Jan 27 2010, 07:12PM
Location:
Posts: 2
Thanks for the reply. From what it looks like, the drain of the bottom left transistor is connected to the gate of the second transistor through a 10-ohm resistor. That doesn't look like an H-Bridge to me...it looks like the transistors are in series - one driving the other. That's what I'm trying to figure out - why is that setup like that?
I'm also curious what the purpose of the diodes are - especially the diode D2 between the drain of the bottom left MOSFET and the source of the one slightly above and to the right of it.
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
I think what's going on is that one pair of transistors is on when the tl494 output is low. The base is directly at the supply. Then the tl494 comes on and the first transistor is turned off by the second one in the pair. It acts like a pull down to the base of the first and also a sink for the current through the primary. So the current that usually turned on the first transistor is drawn away following the path of least resistance and to the collector of the bottom one and into the flyback primary. That looks like it's way too much trouble compared to a simple GDT driving an H-Bridge. After all that's what I think all those resistors and diodes are for... to isolate the bridge and use a discrete driver scheme instead of the GDT.
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.