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
I want to use a GDT with dead time (to control power to my bridge) but I am getting some problems with the gate voltage "overshooting" zero as it returns. Here's a pic of what I'm talking about:
The GDT is 10T trifilar winding on fairly large ferrite toroid, I'm using 5nf caps as a load with 10R resistor in series.
I think it should not be a problem since the primary voltage "flies" anyway to the other rail, so if the other FET slightly turns on it should not matter.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Marko wrote ...
What's the driver circuit? Do you use schottky diodes across the outputs?
The gdt driver is ka3525 and 2x tc4422's. The gdt primaty waveform is fine, the problem occurs just on the sec. side. Increasing gate resistors seems to eliminate the problem but of course they slow down the switching speed.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I don't know what to tell you... do you have some pics of the circuit?
All I can think off is to reduce the amount of turns in GDT to minimum and use shielded cable for windings. It helped a lot to me. And use Schottky diodes.
Registered Member #76
Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458
you should build your halfbridge and check the gate drive signals on the bridge directly with small voltage applied to the bridge. cause the gdt secs are connected to the source of each mosfet, they will hold down to that source potential. theres no need to worry about switching that fet on. ive worked long on gdts with many different turns, dimensions etc but never with deadtime. ive read about adding gate source resistors in the range of several kohms to prevent turning the fets on while in deadtime, that was found on some ti app notes.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Id suggest 1) make your DC blocking cap quite large if possible (1 to 2uF is plenty), and 2) add a small amount of resistance to the primary of the GDT. That seemed to help my issues with GDT drive of this nature.
Im not convinced that you are saturating as its usually more dramatic than a constantly sloping waveform. I do think your GDT is less than ideal (you could probably make one thats better than the coil-craft ones).
Banned on 3/17/2009. Registered Member #487
Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617
jmartis wrote ...
Does anyone have axperience with the Coilcraft GDTs ? (if the link doesnt work please copy and paste
http://www.coilcraft.com/pwrbase.cfm
Ive sampled them before. They suck. They have tons of leakage inductance and ring like crazy. Plus they cost about 5 bucks a piece. Much better to just wind your own. They would come out much better too.
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.
GDTs and dead time
