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.
Account deactivated by user request on 6/11/2009. Registered Member #1071
Joined: Fri Oct 19 2007, 02:13AM
Location:
Posts: 44
I thought I would post this as a story about inductance. The goal was to build a small pulser that put out 10 kA with a rise time of about 100 ns with a charge voltage of less than 20 kV.
So the components were a 100kV 80 nF capacitor with 20 nH inductance and a spark gap switch that is triggered by dropping the air pressure from 20 psi to atmospheric. Initially I connected the capacitor to the switch with a piece of 60 kV floppy HV cable about 6 inches long then I went through a 5 ohm resistor to a ground strap that was about 4 inches long back to the other side of the capacitor. I was using a Northstar HV probe that is 80 MHz bandwidth I think.
So withj 10 kV charge the risetime with the above described setup was about 300 ns and the peak current was around 1 kA. The peak voltage was around 5 kV so the load was approximately matched. Ok so what this tells me is that the pulser impedance is about 5 ohms, which must be pretty much entirely inductive.
So, that was an utter failure.
This was then rebuilt by using a flat piece of copper that was about 10 cm wide from the positive terminal of the capacitor about 2 inches long to the switch, then to the same 5 ohm resistor, then another flat piece of copper 10 cm wide about 8 inches long to the ground of the capacitor.
At 10 kV charge this time there was 8 kV across the resistor. From a simple voltage divider circuit you can figure that the driver impedance must be about 1.25 ohms. So, with an ~1.25 ohm resistor this device put out about 4 kA peak current and the risetime was about 120 ns.
So the reduction in inductance by using large flat connections that ran parallel to each other allowed the impedance to be dropped by a factor of 4.
This was then rebuilt with a 220nF capacitor, still with 20 nH inductance and it put out about 7 kA with a slightly slower risetime of about 170 ns because of the increased capacitance (due to the rise time going like (LC)^.5, because risetime is something like 1/(1/4*frequency)). At 20 kV charge this will put out over 10 kA, the rise time is longer than I wanted, but it may be possible to speed it up a little by putting it into an overmatched load (at the expense of current).
My goal here was to give an example of how an inductance change can vastly change the behavior of a circuit that is fast. If there are any questions or if something wasnt clear let me know.
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.
Inductance with a fast pulsed circuit
