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 #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi guys,
I'm just curious, how far did the whole thing advance since steve ward's giant sucess with the idea? Anyone built similar things in meanwhile? I'd like to try something like that one day and I'm wondering where to start - like any articles I should go through, and controller chips to look after?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hi Marko
My research interest right now is using sigma-delta modulation of the gate drive to do away with the buck converter part of the QCW altogether. My PLL driver already does that, it dithers the gate drive on and off to keep the primary current at the level you set, and I've proved that my coils work reliably in that mode: the demo coil I built for Shanghai ran for 2 weeks bouncing off its current limiter.
So, in theory all I need to do is substitute a ramp waveform for the current limit pot. My 555-based interrupter already has a ramp waveform in its guts, so it should be easy enough.
I discussed it with Steve Ward, and he thinks it will work.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
I have been working to duplicate the QCW for about 4 or 5 months now and from what I have found the primary current stays relatively constant threw out the duration of the burst. As shown in this scope shot
From what I have gathered you do need the ramp in voltage to obtain this sort of operation but this is just my opinion I could be totally wrong.
You can take a look at my flikr page for my ideas and such from my work with the QCW.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi goodchild,
I'm more interested into the buck converter itself for now just due to it's coolness factor. I would also like to be able to use it for rail modulation of various stuff. I've built a linear circuit with a PNP BJT, but I don't think it's powerful enough to do pulsed modulation (even for a miniature drsstc).
I'm surprised to see you simply using a TL494 for this, I thought some fancy controllers and feedback stabilization would be required. What is the reason though that you used the bottom IGBT as well - I would think it would never conduct any current as all would be handled by it's diode.
I was thinking about using high side switch only with an optocoupled isolated driver and a single high side switch, and one freewhelling diode. I didn't know that such a simple controller arrangement (without current mode control) would work here for high pulsed power conditions, though.
For acheiving the effect on a tipycal (non-pll) DRSSTC, I was thinking to use a microcontroller to measure the current and toggle the drive on and off at a certain level, while also acting as an interrupter.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
I don't use a TL494 any more but I did at one point and it worked ok. The low side IGBT is mainly there to brings the ramp back down after a burst. If you look at some of my scope shots you will see that there is a downward ramp as well, that's just shorter that the ramp up. This brings the voltage back down slowly so that you don't get any flash overs or other nasy operation for bring the voltage back to 25VDC instantaneously.
Yes I did say 25V, you have to have the converter "rest" at a voltage above 0V to help the thing start to oscillate at the beginning of a burst. (note this is for primary feedback type designed)
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Goodchild wrote ...
I don't use a TL494 any more but I did at one point and it worked ok. The low side IGBT is mainly there to brings the ramp back down after a burst. If you look at some of my scope shots you will see that there is a downward ramp as well, that's just shorter that the ramp up. This brings the voltage back down slowly so that you don't get any flash overs or other nasy operation for bring the voltage back to 25VDC instantaneously.
Yes I did say 25V, you have to have the converter "rest" at a voltage above 0V to help the thing start to oscillate at the beginning of a burst. (note this is for primary feedback type designed)
Hi -
I'm not sure if I understand this, why would the bottom igbt be required to ramp-down the voltage? 'classic' buck approach can still do that with feedback as the load acts to lower the voltage. IMO your design looks just like a synchronous buck, but with igbt's instead opf mosfets - which can't conduct in reverse and hence the bottom igbt does nothing, it's diode carries all the current. Looking at your schematic I would think that you can take off the drive from the bottom igbt and the circuit should still work the same. (?)
Which controller are you using now, by the way instead of tl494?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hey Marko
The synchronous buck is necessary because Steve Ward used it.
I assumed it was needed because the H-bridge has lots of RF bypass capacitance on it. To make an accurate waveform, the buck has to be able to discharge those caps as fast as it can charge them. When discharging, the bottom IGBT does pass current, which gets fed back to the DC bus cap bank.
Put another way, the synchronous buck can pass current in both directions. When conducting in reverse it acts as a boost converter. It's often used as a DC motor drive where it allows regen braking.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Interesting, looks like I could get away with an sg3525, a gdt and a half bridge brick quite well then?
Only worry left is the inductor - goodchild's one looks really small for any serious peak current! I thought of using ana ir cored inductor but a 500uh one would be rather big. Also, this circuit seems to run in discontinuous mode to me, hence I can't use a powdered iron toroid for the inductor core (has to be gapped ferrite/air core?)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've seen this mode referred to as "forced continuous current" mode. The inductor current is actually continuous at all times: if the current drawn by the load is less than the troughs of the inductor's ripple current, at which point a normal buck converter would go into discontinuous current, then the inductor current goes straight through zero and turns negative.
Same as a Class-D audio amp. When one of these is idling, the current delivered to the speaker is zero, but the inductor current is a triangle wave of an amp or two, symmetrical about zero. Class-D amps are made this way to avoid a transition between discontinuous and continuous current, which would cause a lot of distortion.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Steve McConner wrote ...
I've seen this mode referred to as "forced continuous current" mode. The inductor current is actually continuous at all times: if the current drawn by the load is less than the troughs of the inductor's ripple current, at which point a normal buck converter would go into discontinuous current, then the inductor current goes straight through zero and turns negative.
Same as a Class-D audio amp. When one of these is idling, the current delivered to the speaker is zero, but the inductor current is a triangle wave of an amp or two, symmetrical about zero. Class-D amps are made this way to avoid a transition between discontinuous and continuous current, which would cause a lot of distortion.
So even though the converter always runs in continuous mode, I presume there's too much ripple to use powdered iron cores?
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.
Pulsed power buck converters for DRSSTC drive
