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 #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...
find it weird everyone is so anti magnet wire. Thats what it was designed for.
Actually its not. Magnet wire is not designed for voltage insulation. Its only enough for turn to turn insulation which is not much voltage. High voltage transformers that use magnet wire have teflon or similar sleeving or wraps between the windings for voltage stand-off.
The whole reason for GDTs is voltage isolation. You have a 15V referenced circuit to ground coupled to a floating bridge that can swing +/-400V. You NEED to use insulated wire between windings. Magnet wire is not designed for this period.
wrote ...
The waveforms are really terrible, the output from the PWM chip seems to be pretty decent though.
My core material is ferrite but is type 77 material which only has a permeability of 2000. I used this because it was reccommended.
Yes they are. For your design, you need a 0.1uF capacitor in series with the gate transformer. Type 77 material is absolutely fine for this coil. Thats all i use.
So in summary, its either your blocking capacitor is wrong, your core is wrong, or your transformer is just built wrong. Also, did you measure the frequency output? Make sure its 300kHz.
wrote ...
Heating of Gate Drivers
Yes, this is correct and expected. Remember, your driving continously (CW), so they will get pretty hot, as opposed to a DRSSTC, which runs at very low duty cycles.
Registered Member #1383
Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27
Hey all and thanks for the replies again,
what is your core made of? Where did yo get it? Are you sure it is designed for HF use?
The core is ferrite, type 77 material permeability of 2000, came from a store in south Australia called minikits.com.au. I can't be 100% sure about them, but Eastern Voltage Research reccommended the material.
Should I buy a new core type and if so can anyone reccommed a decent store in Australia?
You should send also the wave forms of the GDT drive output without load...
I'll try that later but before I start disconnecting everything I'll test it out as is a little more. I recall my previous waveforms on an unloaded GDT were pretty decent (on the old enamled ones at least)
Your topload looks very nice, but I'm affraid that the ring is too fat for producing a proper corona-like discharge...
I had thought the same thing, but during the time of construction I didn't know a great deal about those type of design details unfortunately.
There should be a little pot to adjust VCO on the PWM.
Did you play with this adjustment to get max spark?
I've been adjusting the frequency for optimal spark length, I've got a 330pF cap and a 20k 20 turn pot with a 1k fine tune pot for the oscillation frequency adjustment. I've checked right across my range and the optimal frequency is around 285kHz.
One thing to try is connecting your scope directly across the output of the driver chips, that should look like a very clean square wave.
Ok these are my results with the GDT connected but no HV DC input to the board. I've recorded the waveforms and plotted them in MATLAB. The pulses occur at around 285kHz though changing the frequency did not alter the waveform (except of course its frequency).
For your design, you need a 0.1uF capacitor in series with the gate transformer.
Yeah I got a 0.1uF cap in series with each of the GDTs.
So in summary, its either your blocking capacitor is wrong, your core is wrong, or your transformer is just built wrong. Also, did you measure the frequency output? Make sure its 300kHz.
So my blocking cap seems ok, more core is essentially the same as the what has been used successfully previously (part number F-140-77 on cwsbytemark.com, the OD is 35.5mm), I've not used CAT5 wire, just standard multicore flex about 0.2mm copper. I knotted an end and twisted the three wires until there was probably about 1 twist per 20mm then looped it 15 times through my core.
I mentioned this above, it could be the problem but when I had printed the board, I (unintentionally) didn't inverse the two secondaries on one of my GDTs to create the required 180 degree phase shift to the seperate MOSFET pairs. To get around this I've had to switch the pimary polarity on that GDT. Could this cause unwanted signal induction? I'd have to remake the board to fix this up.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
The .1uF cap is probably far too small for good performance. When driving anything but tiny mosfets, i find that you need at least 1uF of DC blocking cap to keep the output from sagging terribly. I often use 10-20uF of ceramic (dont use tantalum or electrolytic due to higher ESR) capacitors for high performance gate drives.
Registered Member #1383
Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27
I've disconnected my GDTs and measured the signal outputting from the driver chips and they look good. Here is a plot of what I measured. I'm going to take more measurements on the loaded signals, I've rewound my GDTs (this must be about the 4th time at least), and I used CAT5 wire. As far as doing a high pot test Ive got a 7k transformer that I could use but its a little sketchy, so I might take the risk (famous last words).
I'll post up my signals outputting across my GDTs later.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
When you make a measurement after winding the new transformer, measure the following:
1. Take a differential measurement of each secondary winding - NO LOAD (not connected to anything) 2. Take a differential measurement of each secondary winding - connected to bridge 3. Measure the frequency
Registered Member #1383
Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27
Ok sorry about the delay but I've taken some measurements. My CRO won't allow differentiate measurements to be read to the computer unfortunately, so I have just taken some photos, a little dodgy, but it should do the trick.
Dr. GigaVolt wrote ... 1. Take a differential measurement of each secondary winding - NO LOAD (not connected to anything)
These measurements turned out to be really very nice, what I would expect they should look like.
GDT1 Secondary A
GDT1 Secondary B
GDT2 Secondary A
GDT2 Secondary B
Dr. GigaVolt wrote ... 2. Take a differential measurement of each secondary winding - connected to bridge
These are my (appalling) signals when connected to the bridge. Looking at this set of results now it seems there is a problem around the gate circuitry somewhere.
GDT1 Primary
GDT1 Secondary A
GDT1 Secondary B
GDT2 Primary
GDT2 Secondary A
GDT2 Secondary B
Dr. GigaVolt wrote ... 3. Measure the frequency
The frequency measures to be pretty much 285kHz. The ring and ball addition to my discharge terminal probably plays a significant factor in altering the resonances.
Registered Member #1383
Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27
Ok the reason that the signal on GDT 2 looked like crap was because a pair of zener diodes on one of the gates were dead (shorting). After a repair to the baord, all of my secondary waveforms look the same - the amplitude is slightly lower on GDT2.
This is a plot of the waveforms on the all of the secondaries of the GDTs (they all look more or less exactly the same now). How closely do these waveforms actually represent the pulse signal? Do you think this has something to do with the cap in series?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Cotlone wrote ...
Ok the reason that the signal on GDT 2 looked like crap was because a pair of zener diodes on one of the gates were dead (shorting). After a repair to the baord, all of my secondary waveforms look the same - the amplitude is slightly lower on GDT2.
This is a plot of the waveforms on the all of the secondaries of the GDTs (they all look more or less exactly the same now). How closely do these waveforms actually represent the pulse signal? Do you think this has something to do with the cap in series?
cheers
That still doesn't look "good." I think your transformer design is still a bit off. What kind of core do you have again?
Registered Member #1383
Joined: Mon Mar 10 2008, 11:09AM
Location: Wollongong, NSW
Posts: 27
Well it was supposed to be type 77 material. The part (FT140-77) came from and is detailed in this pdf under the ferrite cores column.
It basically says "77 Material is reccomended for suppression of noise... ...Noise Attenuation 0.5 to 50MHz".
I chose this because you recommended it in the PSII documentation, but this core seems as though the ones I'm using could be wrong. Surely there's only one type 77 material...
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.
PlasmaSonic II based SSTC, with poor performance
