Re: SSTC Gate Drive Transformers - What's Your Design?
ragnar, Thu Dec 21 2006, 10:46AM

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,
Matthew





And now a schematic for you:

Re: SSTC Gate Drive Transformers - What's Your Design?
CT2, Fri Dec 22 2006, 04:34AM

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.

Re: SSTC Gate Drive Transformers - What's Your Design?
Andrea87, Fri Dec 22 2006, 10:31AM

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

Re: SSTC Gate Drive Transformers - What's Your Design?
thedatastream, Fri Jan 05 2007, 05:21PM

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.

Thanks,
James

Re: SSTC Gate Drive Transformers - What's Your Design?
..., Sat Jan 06 2007, 05:30AM

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.

Re: SSTC Gate Drive Transformers - What's Your Design?
Dr. Shark, Sun Jan 28 2007, 08:40PM

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