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
Question! If the coil is not switching in class-e operation, or very close to it. This would lead to hard switching of the mosfets and eventually premature failure from heating?
Firstly, many SSTCs (and power electronics systems in general) do not switch in Class-E and they work just fine. In any power switching system you basically have conduction losses and switching losses. These are generally pretty similar in magnitude and add up to give the total amount of heating in the transistor switch. SSTCs and other power systems that aren't based on Class-E are designed to get rid of the total amount of heat generated by the conduction losses and the switching losses.
In contrast, a system designed to operate in Class-E has the potential for greatly reduced switching losses. When tuned correctly turn-on losses are almost eliminated and turn-off losses are also slightly reduced. This means that it is tempting to size heatsinks and fans to be only sufficient to get rid of the heat generated by conduction losses. This is fine provided the tuning stays perfect and there are virtually no switching losses to speak of. You only have significant conduction losses so only 50% of the previous heat to get rid of.
However, if the tuning is not perfect the switching losses suddenly return. If the switching losses equalled the conduction losses then you would suddenly have twice as much heat to get rid of. A poorly designed system with inadequate cooling may not be able to tolerate a 100% increase in dissipation in the switching device causing it to fail quickly. So the situation does not appear good for a detuned Class E amplifier. And what makes matters worse is that the addition of the drain-source shunt capacitor actually makes switching losses much much worse when the Class-E amp is not tuned correctly. The peak current through the MOSFET is often higher for resonant switching topologies like Class-E too. This means that although operation is incredibly efficient when perfectly tuned, it degrades very rapidly to something that can be worse than normal hard-switching when the tuning is incorrect.
Most professional systems that use Class-E amplifiers tackle this intolerance of load mismatch in two ways. They either over size the power devices and heatsinks so that they can dissipate the total conduction and switching losses that result from wrong tuning without burning up. Or they install protection circuitry that detects abnormal tuning (called high VSWR) and shuts the Class-E amplifier down before there is time to generate large amounts of heat. Both techniques have their own advantages and disadvantages.
If you really want an RF amplifier that can drive into all sorts of mismatched loads then go for a Class-A amplifier. The efficiency is terrible but any amplifier that already dissipates 75% of its input power as heat is unlikely to suffer any bad consequences even if there is full reflection of the output power. It would only increase thermal dissipation by another 25%!
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Thanks you guys!!! Great info and very appreciated answers!! Richie, You should be a moderator!! If i had electronics teachers that could answer questions like you i probably would not have had to ask in the first place! You guys are great! I couldn't have asked for a better explanation!!
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
One thing i can see in your photo is that your gdt is not bifilar wound. If you have a signal at the input side and not at the output side, that might be your problem. The primary side may not be causing enough induction into the secondary.
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.
high frequency coil very sensitive to nearby objects
If i had electronics teachers that could answer questions like you
