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Marko

Fri Jul 07 2006, 10:57PM

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

Hey Firkragg

That looks great! What frequency 'as is' does it work at?

BTW, I think a ZVS with a buck converter before it isn't such a bad idea as it sounds. If you used the 12V winding on an ATX transformer as the primary, it could get you into the 150V ball park. I once tried a ZVS using the 5v winding as the primary, and the output gave 300-350V DC when rectified (with a voltage doubler iirc)

And of course the buck converter lets you regulate the output.

I scoped everything and ATX transformer simply doesn't fit my desires

From 12V winding I got some 200V from that wierd transformer.
Problem with ZVS is that resonant rise givesme about 35V on primary (measured) and ratio of ATX transformer is simply too high.
Autopsy showed about 7 turns on each primary wich is way too much for 12V input voltage and some reasonable power/frequency.

I would rather need something like 1:3 transformer for this, with low number of primary turns to maximize power output.

When I add a buck converter it becomes pretty lossy and I have no advantage over flyback converter

(maybe I do a little, snubbing is not needed ans so.)

Coil is operating at 1.4Mhz, wich may drop a bit with huge streamer loading.
I need to dinamically tune class E stage now

Next will be adding an interruper and casting a ball out of poliester, I really don't want that ceelluloid ball to die again

PS:
Steve, if I remember there was a 'controversy' about your PLL circuit (I'm using it in this coil) that it goes nuts and cannot lock if interrupter cicles are too short.

So am I going to have trouble with it, or I can get away using inhibit or audiomod input to 'turn off' VCO itself?

Maybe best for me to find out myself.. tommorow..

liquidFire

Sat Jul 08 2006, 12:10AM

Registered Member #479 Joined: Thu Jul 06 2006, 07:06PM
Location:
Posts: 3

Firkragg wrote ...

Great little coil liquidfire

And welcome to (new) 4HV..

Thanks a lot!

Your coil looks very cool, I realy like it.

Firkragg wrote ...

From 12V winding I got some 200V from that wierd transformer.
Problem with ZVS is that resonant rise givesme about 35V on primary (measured) and ratio of ATX transformer is simply too high.
Autopsy showed about 7 turns on each primary wich is way too much for 12V input voltage and some reasonable power/frequency.

I get a little bit more than 120V out of my boost converter, running without regulation.
With regulation, I get the 50 to 95V that I want.
Maybe you could use a similar regulation to limit the output of your converter, just use a few-hundred ÂµF cap, and then switch the converter on and off, depending on the cap voltage. It's not the best way to get a regulated output, but it's simple and good enough for a TC.

Marko

Sat Jul 08 2006, 12:19AM

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

PWM regulation isn't a problem with buck, boost or flyback converter and etc.

Point was that making a self-oscillating ZVS driver (wich is very efficient and cannot be regulated) and then regulating it with buck converter wouldn't be practical in this app.
It's better to use something like simple flyback converter or so.

Steve Conner

Sat Jul 08 2006, 09:16AM

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

Hi Firkragg

I tested my Mk.1 PLL circuit with an ordinary SSTC running off a big 300V DC filter cap and an interrupter. It seemed to work fine. I think it only causes trouble with DRSSTCs because their pulses are much shorter. Steve Ward actually made a modified version of my Mk.1 circuit, so if you have trouble with the original, but still want a PLL, you might want to try his. I think he took the circuit from my Mk2 driver that helps it lock on short bursts, and threw away all the other complicated stuff.

Marko

Sat Jul 08 2006, 12:21PM

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

I'l settle this out then.

One more thing here is that I brought back antenna feedback again for higher power shots, looks more reliable for now.
Base current feedback does something strange, when spark loads the coil it detunes and if I disconnect power supply PLL locks to another harmonic of the coil

(yes sparks are that big)

I need to increase VCOin voltage again to restore the oscillation, and then flip it back while coil is working to get maximum spark.

Transformer I used was lashy from some old monitor, I guess I should strenghten the feedback by using better transformer.

I'm using 100nF DC blocking cap and 10k burden resistor to ground, to reject noise.

Another transformer I tried woked better (but was clumsy) so I guess problem is there.

ragnar

Sat Jul 08 2006, 01:01PM

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

Exhibit A) World's smallest gate-driver transformer wound around a ferrite bead (for small 2N7000 MOSFETs) with 0.15mm enamelled copper wire. I'll explain this one later. Yes, that bead is about 4mm tall.

Exhibit B) Resonator with fundamental frequency of 3.45MHz wound around 25mm PVC pipe, pictured next to a 7KG reel of the 0.15mm wire used to wind it.

Exhibit C) Breakout from the screwy (ha ha) topload at 25Vin 1.5A

Exhibit D) Top waveform is D/S shunt capacitor voltage, bottom waveform is my scope probe hanging near the top of the secondary.

Exhibit E) The whole mess not really doing much whilst I design a more powerful gatedriver. The isodriver is approching his limits.. =)

Marko

Sat Jul 08 2006, 01:17PM

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

I was about to make my own GDT (for main mosfet) but I'm unsure if it is needed actually.
It may just cause ringing and mess.

Sine input at gate is actually good for class E amp, richieburnett used 2 stage class E driver (almost completely sine signal was fed to main mosfet's gate) and he used the amp for 300+ watts without problems.

Your spark looks good but I wouldn't actually call that screw 'topload', it has sharp corners

And I admire your roll of wire, where do you get all that stuff...

I see you cared a lot about your tnak cap, mine is nothing to be desired

(puny 10nf ceramic cap wich is probably way overrated and gets very hot).
Are these high voltage 1nf caps?

ragnar

Sat Jul 08 2006, 01:34PM

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

They're 250pF 10kV caps, the only caps that small I've got that aren't 50V ceramics. hehe ^^
I've got them configured to give me a 375nF shunt.

Screwy is just masquerading as a topload, the idea being if I want a topload I can bolt it on easily. For now, he just stops the coil breaking out at the edges.

Marko

Sat Jul 08 2006, 02:54PM

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

I just filled a ping-pong ball with poliester, it must be dried before I put it to use as topload.
The one I was currently using already started buldging and I don't want it to die again.
^^this means coil waits for a while now.

Maybe you could make yourself something similar

I see you have acces to various CNC machines over there.

What is your current max-spark length?

GimpyJoe

Sat Jul 08 2006, 04:46PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

I had a ping-pong ball catch fire once. That was impressive. I was playing with a jacob's ladder and my friend said "if you put a pingpong ball in there will the arc go around it in a curve?" So we tried it and it burst into flames a foot tall and burned away into a little tiny pile of soot.
Back to the topic, however; you could use a metal drawer pull instead of the ping-pong ball for a topload. You could also just make an actual ball of foil. I made a topload for one of my early coils that was just a bunch of foil compressed and smoothed until it was almost a solid chunk of aluminum, then worked with a small hammer until it was round.

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