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flaming mini TC with single IRFP450

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ragnar

Sun Nov 04 2007, 05:16AM

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

Whilst this is by no means my first SSTC, it's the first one I've ever put into a box and called "finished"! I feel sad for not taking more photos of this whilst I was building it.

Most of the bits (including the IXDD414 driver) are surface-mount. I'll never again attempt to solder down a TO-263 device with just a soldering iron; it was a pain in the arse, the copper on the board didn't have enough area to heatsink it properly, and was too thin to transmit much heat well, anyway. I'll have to buy some solder-paste and try my luck at toaster-oven reflow someday.

You just pop up to 40V in the side and that goes straight through the single IXDD414 into the primary. There's an 8-SOIC regulator for the oscillator and the cliched blue LED ^_^

I didn't have the guts to commit to fixed-value resistors, but I guess I can always do it now since I'm not going to change the secondary in a hurry :)

The aluminium box itself is connected to the base of the secondary and one end of the primary, so only one feedthrough needed for the hot wire after the DC-blocking capacitor. The aluminium box is 50mm x 50mm x 30mm.

A while ago I called for people to show some interest in smaller coils, but there wasn't much response. This coil didn't take long! Will someone else try their luck?

CT2

Sun Nov 04 2007, 05:38AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Man that thing looks sweet, I love the small coils. Takes alot of ingenuity and skill to make something like that. Great work. I tried to build a small coil but it wasn't especially small when all was said and done.

...

Sun Nov 04 2007, 06:10AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Proof that coils and girls can coexist

Amazing work, I have a hard time getting tube coils work at over a MHz. And that is a pretty decent sized discharge considering that the switch has no heatsink and you are running at 4mhz more or less CW

Keep up the good work!

ragnar

Sun Nov 04 2007, 06:23AM

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

Cheers! I'm pleased enough with the result. Initially, I did want to cram a proper class-E coil into the box, but then I started to realise the difficulty of fitting the magnetics and caps in, so I compromised my principles to satisfy the plasma cravings.

The best part about this is that I know I won't be tempted to cannibalise the coil for parts; and because the primary is tight-fitting and held in place by the secondary which is screwed down, quick and easy plasma is as easy as plugging the coil in! No messing around with alligator leads, but just power supplies... :-/

Eek, the IXDD414 is starting to melt itself off the copper cladding. Next time I'll have to go with a TO-220 properly screwed to the inside of the case.

What do you think? Any suggestions?

uzzors2k

Sun Nov 04 2007, 08:52AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

That's a great display piece. A class E version would be nice.

Marko

Sun Nov 04 2007, 10:28AM

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

Hey Matt, beautiful coil

But you didn't care much how your board looks did you

Why did you need that much pots in there?

TO220 IC on large heat spreader might be a good idea... Do you use Schottky diodes across outputs in case of hard switching? I wouldn't really trust mos diodes in this application...

BTW, I think that it wouldn't be hard to use some kind of feedback, like a CT directly into IC's input? ,)

A class E version would be nice.

Class E coils are much more difficult than they may first look - and they work best in all-around-the-table mode with fixed oscillator. They want very fine and constant loading and frequency - and really hate to be moved around, held and hugged.

By using secondary feedback PLL I just made things worse than they would be with open loop. After I boxed it up I never really managed to tune the coil properly and with small heatsink I had inside I couldn't achieve even like half of CW arc size at 1Mhz which Richie Burnett did at 4.

And I also think it would be great hassle to put all the required components in a small box like this.

Marko

ragnar

Sun Nov 04 2007, 01:47PM

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

I'm tying to work out which looks better, the coil or the girlfriend! Naw, even though it's boxed up, it really doesn't look that good... it just looks like every other SSTC out there, except crammed into an aluminium box.

Some day I'd like to really play around with tapered coils with different secondary winding colours (black, blue), and design something ornamental to go over it that A) keeps fingers out, B) reduces the RF emissions, and C) looks good.

Perhaps next time there's a rainy day here, I'll pull it apart and fix some things up... including going with TO-220 drivers. But, the coil itself isn't new or unique (see Roffesoft and Jimmy's IXDD-based coils), isn't all that small in comparison, and the Fres isn't that high...

wrote ...
...But you didn't care much how your board looks did you...

Aw, I cared whilst I was designing it, but it quickly became apparent when I was trying to cut it out with a hacksaw, and when I had to mount all the extra stuff in the box that it wasn't going to be pretty. It looked great with just the surface-mount stuff on it! :P

wrote ...
Do you use Schottky diodes across outputs in case of hard switching?

Yep, I've got surface-mount 1N5819 Schottky diodes clamping the output to the v+/gnd rails. I'm not sure how hot they get, since I can't fit my fingers down there to touch them.

wrote ...
Why did you need that much pots in there?

They're involved in various parts of the driver like fine-tuning the RC, and varying the duty cycle that the IXDD414 sees. In due course, I could replace each pot with a fixed-value resistor... assuming the tolerances were good enough... maybe.

The main thing that worried me about fitting a class-E coil in the box is that there'd be little space between the flywheel/network components and the edges of the box... and the inductors' Q would turn to crap because they're surrounded on six sides by masses of ground.

I suppose a real challenge next could involve fitting two boards in there; one with a better driver, and the other with a TL494 and MOSFETs to drive a little ferrite transformer to provide proper audio modulation... that would probably take at least two rainy days, however. =P

Tom540

Sun Nov 04 2007, 10:42PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Haha, thats cool! I was wondering when you'd get one finished enough to box it up.

ragnar

Mon Nov 05 2007, 05:32AM

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

Wee, salty water. I think having finished projects makes me more prone to distraction!

Firnagzen

Mon Nov 05 2007, 09:03AM

Registered Member #567 Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147

Ooh, nice coil! How many turns are there on it? (Approx, of course)

Also, I have a question- Will this circuit:

run a tiny tesla coil? If it does, I'm going to try one really tiny one someday. I wonder if I can beat the size.

Though of course, the smallest is that 3cm one I saw some time back. Nanotess or something, I think!

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