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Schematic submitted for review.

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Dr. Dark Current

Tue Mar 03 2009, 07:28AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Why do you want a CT? I found that antenna is more stable, especially with ground arcs, and doesn't blow FETs nearly as often.

Ultra7

Tue Mar 03 2009, 03:37PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

Dr. Kilovolt wrote ...

Why do you want a CT? I found that antenna is more stable, especially with ground arcs, and doesn't blow FETs nearly as often.

I was attempting to get all the guts of the coil into a Computer ATX case, with only the primary/secondary on the outside. The antenna added another component on the outside of the box, and I was worried about it's proximity to the actual Pri/Sec.

Arcstarter

Tue Mar 03 2009, 07:48PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Dr. Kilovolt wrote ...

Why do you want a CT? I found that antenna is more stable, especially with ground arcs, and doesn't blow FETs nearly as often.

Well, the reason i changed to CT is actually because oscillations where unstable with antenna. I could not draw the arcs down small, or oscillations would stop and sometimes blow bridges. I am guessing that this is true for some, and not others.

Also, if you are too close to the antenna or something touches it, the oscillations begin to act strange, and i notice significantly more heating on the bridge when this happens. Having everything in a metal or shielded by other means case, i would think that having the antenna so close to the grounded box might interfere, and perhaps require being closer to the secondary due to capacitive coupling to the grounded box.

Also the arcover problems and corona, but this could be solved having a shorter antenna closer to the resonator. but that just means more shielding needed.

There are however drawbacks to CT i am sure, but i have done little study, i just go by my experience.

I thought i posted this hours ago..

That is mine, from the 74hc14 it just goes to the ucc's and such. As simple as it could get as far as switching to CT. It worked well, and the oscillations where much more stable and it didn't die quick (it finally did, somehow the 10k resistor like exploded, it never even got slightly warm in normal operation).

Good luck, Mike.

LithiumLord

Fri Mar 06 2009, 03:29PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Tom540 wrote ...

You could eliminate the zeners and shottkys on the secondary base input. Interrupted sstc's are only screechy if you run them at a high frequency with a low duty cycle. I use 10uF on my GDT primary.

yeah - and how about the fact that the CT has to be burdened? ;)

As for the interruptor sync, after that blow a year ago I decided to implement it and it really came in handy as the heat level is very-very slight now. Myself I use a dual RS flipflop however, utilizing it's third state (both set and reset are present). Each half of the flip-flop acts as an enable controller for one of the two output channels.

Tom540

Fri Mar 06 2009, 04:52PM

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

LithiumLord wrote ...

All you really need after the CT is that series cap D3 and D4. The signal coming in a high impedance and has very little current.

-Tom

LithiumLord

Sat Mar 07 2009, 04:42PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

>The signal coming in a high impedance and has very little current.

...resulting in an insufficient load for the CT that causes a dynamic phase displacement that already caused numerous blows in DRSSTC projects ;)

Tom540

Thu Mar 12 2009, 11:21PM

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

LithiumLord wrote ...

>The signal coming in a high impedance and has very little current.

...resulting in an insufficient load for the CT that causes a dynamic phase displacement that already caused numerous blows in DRSSTC projects ;)

Ive built over 60 coils using that same combo and exactly zero times has it caused a blowing of anything. This is with secondary base feedback. The secondary has very small current feed it through a 60:1 CT and it has even less. If you burden down the CT it will pretty much nill the feedback signal. This isnt the case with primary feedback though.

teravolt

Fri Mar 13 2009, 04:58AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

the original SCH is an old style DRSSTC that uses zero crossing from the secondary. syncronization of the duration to the zero cross is important or fet can turn on at wrong time. this form works but was abandoned for primary zero cross because of instability. please correct if I am wrong

Tom540

Fri Mar 13 2009, 04:28PM

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

teravolt wrote ...

the original SCH is an old style DRSSTC that uses zero crossing from the secondary. syncronization of the duration to the zero cross is important or fet can turn on at wrong time. this form works but was abandoned for primary zero cross because of instability. please correct if I am wrong

Yes but he is using it for a SSTC where primary feedback is not an option.

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