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 #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Dr. Kilovolt wrote ...
Mates wrote ...
Dr. Kilovolt wrote ...
The MOSFET protect itself from overvoltage destruction by mechanism called avalanche breakdown. It can usually clamp the same current as it can switch, limited only by junction temperature.
I disagree Jan, most of today’s FET and IGBT transistors are indeed avalanche rated, but the energy they can handle in avalanche mode is much smaller than the switching energies in case the avalanche switch is repetitive. I have a huge collection of HV spikes destroyed FETs which all could have been saved in case I would use TVS. Avalanche mode is definitely unwanted situation for every transistor and using TVS is something I would always recommend even if the used transistors are avalanche rated.
Well... I have seen your line-powered single switch drivers... I guess then, they simply overheated by the huge amount of avalanche... If you look at a few MOSFET datasheets, you'll usually see something along the lines that the maximum avalanche current is the same as maximum on-state current, and that the avalanche dissipation is limited only by maximum junction temperature allowed.
On the other hand, IGBTs are usually NOT avalanche rated.
OK, I don’t want to argue based on theory and datasheets. My arguments are based on my personal experience. I can suggest you a simple experiment which will cost you an avalanche rated FET, but you get an idea of what I’m talking about. Simply switch the primary of an ignition coil using some robust (16A 600V) avalanche rated FET/IGBT in series with the primary at 3 KHz. As a power source use the rectified mains with some kind of current limiter which will allow maximum of 4A. You will get destroyed transistor very quickly despite the transistor is cold, because of the HV spikes. In case you add a TVS it will protect the transistor, but it will get hot very quickly. Thus, according to my expensive experience avalanche rated transistors are not the same as transitors protected by the TVS in case of repetitive switching of inductive loads in higher frequency rate (above 1 KHz).
BTW: I don’t know how rare are the avalanche rated IGBT’s, but all the IGBT’s I ever had in my hands were always avalanche rated…
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
"Avalanche rated" doesn't mean anything on its own. The manufacturer must qualify it with the avalanche energy and power that the device can stand reliably. This can vary widely between devices.
For high voltage IGBTs, I'd expect it to be much less than the device's rated dissipation, maybe 10 watts or so. Some low-voltage MOSFETs are so good that you can tie the gate to the source and use them as 50 watt Zeners.
On the other hand, the power rating of a TVS is its avalanche rating.
Another important point that I don't think anyone made: A TVS clamps overvoltage. An ordinary diode only clamps reverse voltage. Those are two fundamentally different functions.
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.
how is a TVS different?
