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The Dead simple DRSSTC

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plazmatron

Fri Jun 22 2012, 08:05PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

People keep asking for a simple DRSSTC diagram (presumably without the logic chips), and some time ago I came up with exactly that.

I have had this thing around since the summer of '09, but it was uncased. so I decided to tidy it up, and post it here.
It is of similar dimensions and scale to Steve Wards 'DRSSTC .5', and in fact, it was that coil that inspired this design.

This was designed to be a low power coil with reasonable performance, not a record breaker, so I decided to leave out all of the 5v logic. The resulting circuit it this:

The base feedback CT (AS-103) was purchased from RS components, and feeds pin 2 of the UCC's almost directly. I keep the interrupters separate from my coils, and send the signal over fiber optic to the coil. This is fed into the UCC pin 3 via a cheap, and simple phototransistor. (Maplin part number YY88W).

I use Tosliknk cable, and pulled apart some Toslink adapters, for the sockets. I simply drilled a 3mm hole in the back of the sockets to accept the phototransistor, at the tesla coil end, and a hyperbright LED at the interrupter end.

There is nothing special about the rest. The half bridge is the same as Steve Ward's, except I use 24v Zeners on the gates of the TO-247 40N60 IGBT's, since I lost an IGBT to gate failure.
The resonant frequency is around 450 kHz.

The image above shows the control board in the base of the DRSSTC.

And below, the obligatory spark pic.

As for spark length, I have pushed about 12 inches of spark out of this coil, and it has survived ground strikes, without losing silicon.

This simple driver has worked far better than expected, and hasn't caused any problems. However, as I stated, this isn't a record breaking coil, and has never been pushed hard. It is a perfect driver for ISSTC's, and good enough for low power DRSSTC's. For anything bigger, use proper drivers!

Les

Thomas W

Fri Jun 22 2012, 08:13PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

I think you will find this is a record breaker.... worlds simplest SSTC... ^^

zrg

Fri Jun 22 2012, 08:56PM

Registered Member #4762 Joined: Sun May 06 2012, 05:59PM
Location: Russia
Posts: 93

I believe my SSTC would be even more simple, especially if you use IGBTs with inner diodes (when I was designing the schematic, I used MOSFETs) and magical all-in-one UCC27425 chip for a driver :)
UCCs have embedded Schmitt triggers, so the signal from diode fork can be fed directly to their input gates.
In the latest design I changed the antenna feedback to CT feedback, as it is much more stable in the operation.

Of course no overcurrent detectors or any stuff required for proper driver, but that circuit just works fine enough. Maybe it can even be modified to double resonance...

If anyone is interested, more info is here (in russian, but google translate will save you)

genious 7

Sat Jun 23 2012, 12:46AM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

Correct me if wrong (and I am probably wrong), but isn't this an SSTC? I see you take the feedback from a current transformer and secondary feedback, like a SSTC, not from primary current like in a DRSSTC.

Unless you are hard switching the primary (which I kinda doubt would survive if it was double resonant), I guess its closer to SSTC than to DRSSTC. What is your primary and MMC?

Besides, your schematic is almost identical to Steve Ward's SSTC5; minus the Schmitt Inverters.

Ben Solon

Sat Jun 23 2012, 01:19AM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

You are right- it will hard switch the primary unless it perfectly matches the secondary. It will also it off the igbts mid pulse when you cut off the interrupt signal. The point of the coil is to be as simple as possible, and under 100W it won't immediately kill the igbts, but it will strain them. It's why he says that for any bigger coil you should use a logic board that utilizes zvs and interrupt cutoff timing.

plazmatron

Sat Jun 23 2012, 12:36PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Michael Chen wrote ...

Correct me if wrong (and I am probably wrong), but isn't this an SSTC? I see you take the feedback from a current transformer and secondary feedback, like a SSTC, not from primary current like in a DRSSTC.

This is dual resonant, with a 70nF MMC. The spark length is about twice the secondary length.

DRSSTC's can be run happily off base current feedback, and in fact on small ones, with limited primary current, it is the way to go. Besides, if primary feedback could be gotten to work on this coil, I would then need an OCD, since the primary current would ring way up!

Because I have omitted the hex inverter, and JK-flipflop, from this design, the IGBTs can be turned off, mid RF cycle by the interrupter. This is bad news for IGBTS, so the pulse width is kept low, and PRF is kept low.

It is therefore not quite the performer that Steve's coil is, but was designed to be an experiment to show "What can we expect from a DRSSTC, built from a minimum of components"

I figured, some of the new guys, who have built one or two SSTC's already, might like to experiment with the design, as a 'stepping stone' if you will, to grander coils!

The top of the MMC, is on the bottom right.

Les

Tetris

Sat Jun 23 2012, 06:43PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

@zrg what's the antenna for? Hehe, it is simple. If I can understand it, it has to be simple. xD

plazmatron

Wed Jun 27 2012, 12:49PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

HighVoltageChick wrote ...

@zrg what's the antenna for? Hehe, it is simple. If I can understand it, it has to be simple. xD

The antenna picks up the output from the secondary of the Tesla coil, to use as a feedback signal to drive the coil.

I'm not a fan of antennas, since in DRSSTC use a single strike can destroy the electronics, plus a current transformer makes for a more compact and tidy design.

Les

Dri0m

Wed Jun 27 2012, 02:39PM

Registered Member #4497 Joined: Thu Apr 19 2012, 12:53PM
Location: Behind you
Posts: 62

Tom Williamson wrote ...

I think you will find this is a record breaker.... worlds simplest SSTC... ^^

Uhmmm, Slayer Exciter is SSTC too, and it have only 3 parts, baterry and coil :P

Steve Conner

Wed Jun 27 2012, 03:33PM

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

How about "World's simplest SSTC that doesn't suck" then?

I think Les's circuit could be improved slightly by taking R2 to a DC bias voltage about equal to the UCCs' switching threshold, instead of ground.

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