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 #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
> I saw this effect even after bypassing the GDT, so this effect must be from the stray inductance on the mosfet.
Most likely stray inductance in your wiring. MOSFET designers go to great lengths (or should that be short lengths!) to minimise stray inductance in high-frequency power devices.
> Is this behavior that I want? The voltage "ringing" isn't what I was after; it was the timing delay to ensure both mosfets weren't on at the same time.
I've never seen a zener used in series with MOSFET gate before, although they are often connected across the gate for ESD or voltage overshoot protection of the gate oxide.
The usual way of achieving deadtime is by limiting the maximum duty ratio in the drive waveforms at the control electronics. It's also possible to increase the resistor in the turn-on path of the gate damping circuit, although this really just slows down the turn-on process and increases switching losses. There is an important distinction between "turning on later" and "turning on slower". You can turn on a power MOSFET as late as you like, but not as slowly as you like without it burning up!
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
How do you think I am getting the -20v instead of -15v. Also, how is it that the voltage ahead and behind the diode is the same instead of 5v less?
I am thinking the capacitor is being charged through the inductor, like you said, and this is boosting the voltage after the diode. However, I am not clear on the exact mechanism: the pathway the capacitor is charged and how this brings the voltage after the diode equals to the voltage before, and how the voltage drops to -20v.
EDIT:
I may have answered my question. I scoped the voltage across the diode, which was 5v as expected. I then measured the voltage across the mosfet. With the added inductance to the circuit, the voltage was phase shifted. The 5v diode positive voltage was now occurring almost completely during the negative cycle across the gate-source. This is why the difference is seen on the negative cycle.
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.
zener voltage drop is weird
