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4hv.org :: Forums :: Tesla Coils
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SSTC Gate Drive Transformers - What's Your Design?

Author Post
Thu Dec 21 2006, 08:40AM Print View
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
Hi All,

I'm slowly resurrecting the GDT design guide on my website, and I'd like to know what you all use in your SSTCs, be they plain, DR, bipolar or otherwise. Please reply to this thread with your GDT design specifics. Things that would be nice to know are...

  • Type of coil used in - bipolar, DRSSTC, normal SSTC, other
  • TC primary drive topology - full bridge, half bridge, other
  • Drive Frequency
  • Core style - toroidal, EE, EI, CI, pot
  • Approximate core dimensions
  • Core manufacturer, material type, part number or catalogue number (if any are known)
  • Winding method - trifilar, coaxial, other
  • Wire type used - enamelled copper wire, bell wire, CAT5 cable, other
  • Number of turns
  • AC coupling cap
  • Method of driving GDT primary - UCCs, IXDDs, FETs, other
  • Devices being driven - FETs, IGBTs
  • Secondary series resistance
  • Amount of ringing on waveform

You don't have to know all of the above, but the more info there is, the more useful it will be to others.

What do you get out of it all?

  • A link to your website from the GDT design guide "Existing Designs" page (to be created).
  • A warm feeling knowing that you've helped other people who might have been less knowledgeable than yourself
  • Not having to answer more forum posts on the subject

Thanks in advance,

p.s. happy winter solstice to you all
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Thu Dec 21 2006, 10:46AM
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Posts: 1423
hi James, here's my most recent setup, especially designed for high frequencies

Used in 13.56MHz class-E coil,
the resonator's primary is in series with the MOSFET drain circuit,
cores are large EMI beads/toroids, L=25mm, OD=12mm, ID=6mm,
found sleeved over various power and signal cables inside any monitor,
coaxial winding; CAT5E inner, FOIL outer,
turncount 3:1,
small series decoupling capacitor used to raise secondary Fres,
primary driven using up to 4 x IXDD414 at 12V,
driving a single IRFP450 MOSFET (2.6nF),
no additional secondary series resistance,
GDT resonates, Q~1.2 to 1.5,
leakage inductance? Low.

I'll have a site of some description ready soon,

And now a schematic for you:

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Fri Dec 22 2006, 04:34AM
Registered Member #180
Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187
Here's what I've pretty much used on all the SSTC I've built, don't know exactly how well it works seeing as how I don't have a scope but it seems to get the job done (aprox. 18'' arcs) Link.

Coils being Driven - SSTC Fullbridge of MOSFETS around 100-150kHz (Steve's mini SSTC schem and Conners DWSSTC schem)
Core Style - Toroidal from Electric Gold Mine Size is 1" outer diameter x 5/16" thick with an inside diameter of 1/2" Link
Winding Method - I take about 15 wires, really fine enamelled (from deflection coil of TV), twist them all together and wind 12 turns on the toroid, then seperate the ends and 3 wires are used for each fet and the primary. Its like a super litz wire made of litz wire, I think it should work really well. On the primary there is a .33uF cap and there is 10ohm resistors and zeners on all the gates.
Driving Method - Two UCC37321/22, so one inverting and one non-inverting together with protection diodes on outputs and tantalums+electrolytics on power rails, also copper heat sinks.

And thats about all I can say about my Gate drive... hope it helps.

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Fri Dec 22 2006, 10:31AM
Registered Member #494
Joined: Thu Nov 09 2006, 02:42AM
Location: Udine, Italy
Posts: 31
Driver used for: Self tuning SSTC / induction heater
power stage: Half bridge, FDH44N50, bypassed with 5µF polipropilene
Frequency: between 150KHz (indheat) and 180KHz (sstc)
Core type: toroidal, green color, got it from a friend. about 40mm outer dia x 25mm inner dia x 15mm h
winding method: secondary bifilar close wound, 18 turns, primary wound over the bifilar primary, 10T. wire used: 0,6mmq solid insulated wire.
AC coupling cap: 0,47µ polipropilene
driver: pair of UCC 37321/37322 well heatsinked, bypassed with 1.5µF tantalium + 0.1µ poly, + 47µ electrolitic on the main supply rail
zeners on the gate + 15Ohm resistors

I'm getting good results with this, at resonant frequency ringing is not bad, gate waveform looks good.

some pics:

scope shots coming soon too in the indheat project thread
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Fri Jan 05 2007, 05:21PM
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
Just a note to say that a link to a webpage containing design details would also be great if you can't be bothered to type out the specifics.

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Sat Jan 06 2007, 05:30AM
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2435
I have only made 2 GDT's in my life.
1. filter core (see matt's pics) with pentafillar (5 wires with like 20 turns/inch) 32awg enameled wire, ~20 turns (if I remember correctly). It was fed by a tc4421/tc4422 (in the to-220 package) with a 1.uf dc block cap in the input. The outputs went a a fullbridge of various mosfets/igbt's. My test was driving a 10nf cap on each of the outputs, at 700khz I could drive a sine wave of ~15v. But for long runs the core (not the wires) got too hot to touch, so I decided it was no good.
2. e-goldmine looking core, with 5 loosely twisted cat5 wires (weird ones, they were stranded) and like 10 turns (again, not sure). I was driving a fullbridge of '460s and I think that for +/- 10v (zener limited) I had rise/fall times of 3us or so.
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Dr. Shark
Sun Jan 28 2007, 08:40PM
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Since I think I am the only one using EI cores and also a lot more turns than other people, I'll describe what works for me:
  • Type of coil used in - various small benchtop coils
  • TC primary drive topology - half bridge, single switch
  • Drive Frequency: everything from 200kHz to 3MHz
  • Core style - EE and EI ferrites
  • Approximate core dimensions: pretty small, about 2mm x 5mm xsection
  • Core manufacturer, material type: generic ferrite salvaged from switchmode PSUs
  • Winding method - multifilar (e.g. 5-fillar) so I can put windings in series to step up voltage
  • Wire type used - enamelled copper wire
  • Number of turns - 30 works well, depending on frequency
  • AC coupling cap - combi of electolytic and a small film cap
  • Method of driving GDT primary - UCCs
  • Devices being driven - both FETs and IGBTs. IGBTs definitely need the "two secondarys in series" approach for enough driving voltage
  • Secondary series resistance - none.
  • Amount of ringing on waveform - visible but does not seem detrimental to performance
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