Welcome
Username or Email:

Password:


Missing Code




[ ]
[ ]
Online
  • Guests: 22
  • Members: 0
  • Newest Member: omjtest
  • Most ever online: 396
    Guests: 396, Members: 0 on 12 Jan : 12:51
Members Birthdays:
One birthday today, congrats!
uzzors2k (35)


Next birthdays
03/29 GrantX (34)
03/30 Adam Horden (39)
03/30 Mr.Warwickshire (23)
Contact
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.
Forums
4hv.org :: Forums :: Tesla Coils
« Previous topic | Next topic »   

How can I improve this GDT waveform?

Move Thread LAN_403
Gregary Boyles
Sun May 17 2015, 03:49PM
Gregary Boyles Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
GDTSecondaryWaveforms

Based on Steve Ward's min STTC design: Link2

These are the waveform generated by the two secondary windings of my GDT (1:1:1) with the probe on one end of the primary and the GND clip on the other end.

I have a 6.8uF greencap in series with the primary coil of the GDT.

The inductance of the primary coil and one of the secondary coils is 1.34mH. But for some reason the other secondary has a slightly lower inductance of 1.26mH. It might have something to do with the fact that I used thin hook up wire to wind the GDT and not magnet wire. It seemed more convenient to have the windings colour coded but it is also harder to get the windings tight.

But there are two problems that I can see.

1) There is a lot of ringing going on here. Is that likely to be a problem?

2) My vertical scale is 0.5V and my probe is on x10 so I put the peak voltage at 5V and that is too low. So what is the preferred way to increase the voltage?

a) Increase the value of the series capacitor?
b) Reduce the number of windings?
c) Increase the number of secondary windings?
Back to top
Wolfram
Sun May 17 2015, 06:25PM
Wolfram Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Are you using the same gate drivers as in the schematic you linked to? What voltage are they running from? How many turns are there on your GDT? Is there any load on the GDT secondary when you're measuring?

The ringing is likely caused by stray inductance in the GDT circuit. This usually caused by problems with the circuit layout. Can you post a picture of your circuit?
Back to top
Gregary Boyles
Mon May 18 2015, 12:30AM
Gregary Boyles Registered Member #9039 Joined: Wed Dec 26 2012, 03:31PM
Location: Epping, Victoria, Australia
Posts: 117
Wolfram wrote ...

Are you using the same gate drivers as in the schematic you linked to? What voltage are they running from? How many turns are there on your GDT? Is there any load on the GDT secondary when you're measuring?

The ringing is likely caused by stray inductance in the GDT circuit. This usually caused by problems with the circuit layout. Can you post a picture of your circuit?

The primary of the GDT is running off 12V at present but it will be running off 15V.

I found this excellent resource that explains a lot - about the ringing and about the slightly sloped tops of my square wave.

Link2

The ringing is occurring because the GDT secondaries are floating at present - I have not yet linked them up to the 5 ohm damping resistor in Steve's design.

And it looks as though I could do with a few more turns on my toroid than Steve specified judging by the slight slope at the top of the square wave - Steve perhaps did not use an N30 type toroid.

But unfortunately it does not really explain the best way to resolve the issue of not getting a high enough peak voltage in secondary windings.

Perhaps the web masters might consider creating a page with links to all the resources I / others have found on GDT design - a hub that folks like em can go straight to rather than asking what I am certain are the same questions over and over.

Question regarding Steve Ward's mini SSTC design:
http://www.stevehv.4hv.org/SSTC5/miniSSTCfnlsch.JPG

From this excellent web site: Link2
I learned that R3 and R4 are meant to dampen the ringing in the GDT.

The gate of the FETs form a capacitor with source that connects to either GND or the mid point of the half bridge.

Does the combination of the damping resistor and the gate capacitance amount to a low pass filter that attenuates the high frequency ringing?


Also I hooked my GDT up properly to my half bridge today and found that I have this problem:
Gdtwav05

And according to the above excellent web site, that can be caused by an inadequate gate drive IC. So apparently I have chosen poorly with UCC27425.

But never mind. Due to my so far unsuccessful efforts with a half bridge ignition coil driver I am a great deal more confident with darlington totem pole gate driver, which was working well. Including an inverting totem pole using a 555 based NOT gate on the bases of the darlingtons.

So I will replace my UCC27425 with pair of darlington totem poles - space is not really an issue.

[Edited by moderator Mads Barnkob - merged double post and removed image larger than 600px]

Back to top

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob

Go to:

Powered by e107 Forum System
 
Legal Information
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.