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yet another DRSSTC - reality check

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Steve Ward

Sat Jun 03 2006, 01:19AM

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

If I use primary feedback, I will get ZCS no matter how the phase is adjusted, or even if the frequency is off?

Nope! You want zero phase shift (or ideally, slightly negative phase shift) with primary feedback, and the PLL will not do that on such short bursts with this circuit. Sorry dude, its basically a VCO with other non-useful features.

Dr. Shark

Sat Jun 03 2006, 07:36AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Damn! Well, I've got one of Mr Conners new boards, so I guess I will use that for further DRSSTC experiments. This one is probably better suited to SSTC duty, which is no problem, I'll just take out the MMC and I'll be good to go.

Oh, Steve Ward, before I get Steve Conners complicated (like 10 ICs in there) stuff working, I'd like to have a go at your simple micro-DRSSTC. Do you have any schematics, or is it really as simple as you described it in the other thread?

EEYORE

Sat Jun 03 2006, 04:49PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

joe wrote ...

Damn! Well, I've got one of Mr Conners new boards, so I guess I will use that for further DRSSTC experiments. This one is probably better suited to SSTC duty, which is no problem, I'll just take out the MMC and I'll be good to go.

Oh, Steve Ward, before I get Steve Conners complicated (like 10 ICs in there) stuff working, I'd like to have a go at your simple micro-DRSSTC. Do you have any schematics, or is it really as simple as you described it in the other thread?

It really is that simple!

I got that little coil working on the 1st go...Promply blew its guts out an hour later when i decided to blast it with full power from the variac...Its got to be one of THE most simple sstc's out(in a good way)

...

Matt

Steve Conner

Sat Jun 03 2006, 05:56PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I'm sure I've said it before, but I'll say it here for the record. If you're looking for a simple DRSSTC controller, it's probably best to use Ward's.

My mk2 driver is a full featured design with all the protection needed for a commercial system. It's debatable whether it's overkill for a hobbyist coil. But I stand by the quality of it, and if you can be bothered building it, I believe it makes a damn fine coil.

I guess what I'm saying is, build Ward's driver unless you love electronics for the sake of it.

I don't really have a "My circuit is better than yours" axe to grind any more, so I could care less whose driver you choose.

I'll update my site to give a warning that joe had trouble with the Dirty DRSSTC driver. I don't think anyone else ever tried it on a DRSSTC, and I never really figured out what was going on with it until now when I saw joe's post.

Dr. Shark

Sun Jun 04 2006, 10:02AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Oh come on Steve, I know damn well that your circuits are the finest out there, and since I am a pefectionist I do feel the need to replicate them

Hold on with updating your website though: I did remove the DR part from the coil yesterday and tried driving it as an ISSTC (still interrupted, but much longer on-time, a couple of 100 cycles at least), and still it would not lock. So the problem is more likely to be my implementation than your design. I could still try driving it completely CW, but I doubt that it would make a difference. It still gives nice sparks as an oscillator-based coil, so I'll just leave it as it is. (Well, got to fix those arc-overs to the primary coil, but that's another thing.)

I also noticed a strange problem with my primary feedback transformer: Instead of putting out a square-wave, each time there is a zero-crossing it starts a funny oscillation with about twice the frequency of what the coil is running at. I put it together from two small double-E core transformers, maybe it needs toroids? Once I get that going, I can have some fun with Steve Wards circuit.

Steve Ward

Sun Jun 04 2006, 07:16PM

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

The time needed to lock should depend on the RC filter on the phase comparator output (if i remember the PLL circuit correctly). You can reduce R and C to make it respond faster, but i believe this can cause instability (as with most feedback circuits).

The micro DRSSTC is as simple as i described (hence no schematic). You still have to be careful with the layout, mostly the inductance between gate drivers, GDT and IGBTs. If you chose to use such a circuit (with no synchronous turn off) then you should not run the IGBTs beyond their ratings (i was only running 100A peak with 160Apk rated IGBTs). Also, you will need a tight bridge layout to clamp the *severe* voltage spike that will be present with the hard switching. I really dont recommend it for large coils, as your chances of splattering IGBTs is greatly increased. Its not really that much work to add the flip flop. You could substitute in a D-flip flop as well, provided you have S and R inputs (aka Pre and Clr). If you need any help figuring out the flip flop scheme, just ask.

As to whose circuit is better. Ive always felt that the simpler way is better, just because its easier to understand completely, and when something goes wrong, its not too hard to spot the problem. My circuit starts to fail at high frequencies (despite my micro coil) because there is inherently some delay in the driver and IGBTs, and my circuit does not take care of this at all. So, if your gonna build something under 100khz, there really is not much need for a PLL circuit since you will get pretty darn close to ZCS with decently fast IGBTs. Last i checked, both of our circuits allow for the production of big sparks

HV Enthusiast

Sun Jun 04 2006, 09:02PM

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

When comparing circuits, just remember that there is more than one way to skin a cat. . . i also vote that simpler is better (K.I.S.S. principle), but if you think of a better way of doing something, by all means go for it!

Or combine them both into one mutated mess of a circuit!

Remember, even Steve Ward's driver was a combination of several different ideas - flip-flop sychronization from Dan Strother, and the primary feedback scheme from Terry Fritz. Take your idea and keep on mutating. This is the way these things tend to evolve!

Dr. Shark

Mon Jun 05 2006, 08:46PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Simpel is better. Here is the minimal DRSSCT driver, true to Steve Wards design:

everything, including the interruptor and the half-bridge are on the board, only the MMC will be external. I am kind of scared to test it though, since I have no idea if the GD chips and transformer will be working. Thats really the reason why I liked Steve Conners VCO circuit so much

Oh, the camo background is because I am sooo cool!

Marko

Mon Jun 05 2006, 08:59PM

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

omg omg, the crappiest DRSSTC driver board I've ever seen!

Where is your 74HC14?

Or you are trying to put the signal directly to UCC's?
This will probably work for antenna but I don't know if anyone seriously tried it with current transformers.

Only possibly bad thing I see is the GDT, not clearly visible but do you have windings on both sides of bobbin?
You need tight multifilar winding for very high coupling in GDT.

Jim

Tue Jun 06 2006, 11:55PM

Dunce.
Registered Member #28 Joined: Fri Feb 03 2006, 03:29AM
Location:
Posts: 76

Firkragg wrote ...

Or you are trying to put the signal directly to UCC's?
This will probably work for antenna but I don't know if anyone seriously tried it with current transformers.

Steve just did this...

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