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The DFSSTC (small push-pull coil)

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LAN_403

Marko

Sat Jun 17 2006, 12:21AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

The dirty Friday SSTC is a small and very simple design mocked up in few hours (not counting the secondary from before). Secondary had an overlap and ugly varnish so it was sitting for a while, unused.

I made the driver incredibly simple, with single ICL7667 and IRFP450's in push-pull mode so there is no need of isolated gatedrive.

Oscillation starts without problems (unlike similar single-switch circuit) as one mosfet will always be ON and give the first ping to the coil.

Firstly I ran it carefully on 12V for some 2 cm of spark, and it fell on 1,5 when I increased primary by one turn. (now it's 3+3)

Interestingly increase to 5+5 turns killed output completely but mosfets heated like before.
Seems to be impedance matching problem S. Ward pointed out on his micro SSTC.

Now I managed to series an 18V supply with my 12V one so coil now gets about 30V into the bridge.
Interestingly If I left one supply unfiltered (only bridge rectified) oscillation didn't start.
With filter cap there were no problems.

Streamer was about 3cm long.
I found a small topload and put it on the coil, allowing maximm of 5cm sparks to be drawn from it by sharp object.

With breakout point far away enough it actually boosts performance (lower resonant frequency I guess).

Arc looks a bit fuzzy on the pic.
Probably it could go for much more but crappy 400 miliohm mosfets are already heating quickly and I don't want them dead. I'l try a 100V run once I get enough courage.

IN the end coil is loaded with whole bunch of various bulbs and other stuff around it.

I already have couple of such small SSTC's but I never tried to audiomodulate any.
This one will probably need an audio amplifier to modulate the rails as I didn't mind to use PLL or PWM open-loop drive. That could be an idea for later..

next update:

Hesitating, I finally put the coil to 110V input.
Coil burped, ICL7667 lacthed up, and died a horrid Death.

110V supply was on for just a second but ICL continued to smoke even after it was disconnected,

FIrstly I tought mosfets died, but they both measure fully operational and kicking.

ICL was caved out and split in pieces.

My theory is that drain-gate (miller) capacitance genrated voltage spikes wich latched up the ICL's output stage.

I also lost my mod for doing work on DRSSTC today.

HV Enthusiast

Sat Jun 17 2006, 12:41AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

How about some additional information to what a DFSSTC is, and how it differs from other SSTCs. I'm sure there are people out there, including myself, who have no clue what a DFSSTC is???

Remember, the project board is a place to showcase and describe your coil in full detail. If you are merely going to post a few images of your coil, then please post it on either the chatting board or Tesla coil board.

Thank you

Michael W.

Sat Jun 17 2006, 02:09AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I was afraid to ask what a DFSSTC was in fear of looking like an mental insufficent....

Steve Ward

Sat Jun 17 2006, 07:36AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

From the looks of it, its a push-pull topology with antenna feedback. Im guessing since the last think he said was "bed" that this was a late night post and it will be followed up with some details.

2cm sparks with only 12VDC input isnt too bad really. You could probably run it to 70VDC with the spikes (im guessing those are 500V-600V devices?). Or, if you go class-E you could run quite a bit more.

ragnar

Sat Jun 17 2006, 09:26AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Firkragg, it looks like you have the antenna going straight into a ?gatedriver? chip... =)

How then do you provide the drive to each FET without a GDT? =)

-Matt

Avalanche

Sat Jun 17 2006, 02:25PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Double Fet SSTC?

It looks like the primary is center tapped, with each side being switched in turn by the FETs, therefore you wouldn't need isolated drive signals and shoot through wouldn't be an issue.

Of course this is all guess work based on the picture

Marko

Wed Jun 21 2006, 01:50PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Sorry guys, this was posted after 3 in morning and I wasn't actually aware what was I doing.
I also left town (and computer) next morning, for few days.

Now I drew schematic, some more pics, etc.

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