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 #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
You may be able to set up a high pass filter to the gate or each fet. Below a certain frequency you would just be burning extra power in the devices themselves though. The only way I see it working perfectly is with an active filter however. Or maybe a high pass filter calibrated to the input thresholds of a Schmidt triggered buffer or something along those lines.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Make sure that the resistance and inductance (of wires and pcb traces) is very low between the two sources, and especially between the drains and the primary capacitor.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
That circuit is intrinsically dangerous. Nothing impedes the simultaneous conduction of both transistors, if something, as excessive load, stops the normal oscillation. It burns out not due to high-frequency oscillations (that may occur too), but because the normal oscillation stops.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Short answer: By using a half-bridge driven by a PLL instead.
Long answer: As far as I know, the parasitics start when the voltage drop across the MOSFET that's "on" gets too high to turn the other MOSFET completely off. The partly "on" device functions as a high-gain linear amplifier, and since it isn't neutralised, it bursts into oscillation somewhere in the 10s of MHz. The oscillations heat the MOSFET up, and MOSFET Rds(on) increases with temperature and Vgs(th) decreases, so once they have started they quickly get worse until the circuit goes into thermal runaway and melts down.
Anything that helps the MOSFET turn off completely will help stop the parasitics. Including better cooling, as this decreases Rds(on) and increases the threshold voltage.
However, you then have to face a second problem. The circuit may never start oscillating unless it's biased such that both MOSFETs can turn on at once. Achieving this, while still making sure they turn off completely for most of the cycle, needs very fine control of the DC bias. The standard circuit completely fails to provide this.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Completely different question, so here's a completely different answer. The DC-DC converter circuit used in a car audio amp is similar to the ZVS and could probably draw 100A at 38V easy enough. It uses the same push-pull transformer, but it's hard switched, with no tuning capacitor and the MOSFET gates driven by a fixed frequency oscillator. The transformer is wound on a toroidal core with the primary and secondary wires all mixed together to minimise leakage inductance.
The improvement in efficiency given by zero-voltage soft switching increases as the square of the voltage. For 12 or 24V, maybe even 38V, it doesn't make a huge difference.
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.
parasitic oscillations and zvs
