RE: PLL SSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Leigh Copp" <Leigh.Copp@xxxxxxxxxxx>

Hi Terry,

You're absolutely right; the zero cross detection circuit is the key. An
LM311 works pretty well; especially if you clamp the output so that it
does not saturate.

I tended to favour some of the ridiculously fast Analog Devices op-Amps
like the AD847, or even the AD811 (2500 V/us slew rate!).

The key of course is filtering, and then compensating for the delay.

Another trick way to do this in the digital world would be to use a
constant group delay filter implemented in a DSP. Unfortunately the
built in A/D in most of the DSP's out there are far to slow to have the
single shot (real time sampling) capability to resolve a zero cross at
10's, 100's or even 1000's of kHz. So you would need some pretty awesome
A/D (rather like the front end in your Tek scope) and then jam that data
into something like this:

http://www.analog.com/processors/tigersharc/index.html


http://www.analog.com/UploadedFiles/Data_Sheets/777379751ADSP_TS201S.pdf


But getting back to reality, your bang-bang control method implemented
in discreet logic is simply the fastest (and only true real time) method
to do this.

We settled on the lowly analog PLL, because with it you can control the
loop bandwidth, to match your resonant components, and it presents a
fairly nice package with very little temperature drift, or (internal)
noise.

Cheers,

Leigh



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: September 5, 2006 6:52 PM
To: tesla@xxxxxxxxxx
Subject: Re: PLL SSTC

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

I think Steve Conner has done the most with PLL solid state Tesla coil
stuff:

http://scopeboy.com/tesla/index.html

http://scopeboy.com/tesla/dwsstc/wk2.html

The problem is Tesla coil waveforms like this:

http://hot-streamer.com/temp/NightmareWave.gif

Fricking had for a PLL to track!!  But Steve has been the most
successful!  I think he has better stuff now...

Most other designs use "fast" zero crossing detectors on the primary
current to do it all in real time:

http://drsstc.com/~terrell/schematics/MainController-1.0.pdf

http://drsstc.com/~terrell/schematics/CurrentMeasurement.gif

http://drsstc.com/~terrell/schematics/OpticalGateDrive-1.0.pdf'

http://drsstc.com/~terrell/schematics/H-Bridge-1.0.pdf

Connor, Ward, and certainly Dan do better then "me" here ;-))

http://scopeboy.com/tesla/

http://www.stevehv.4hv.org/SSTCindex.htm

http://www.easternvoltageresearch.com/

The "real thing" would be to have a uP hard number crunch it all in
real time...  I have "imagined" doing it with this:

http://www.parallax.com/dl/docs/prod/prop/PchipBlockRev.pdf

But just "pie in the sky" ;-))

I got some 4046's once but never used them since the fast real time
stuff was better for me.

Cheers,

         Terry


At 10:22 PM 9/4/2006, you wrote:
>Dear forum members,
>
>I believe few members of this forum have used a PLL (4046) to
>'auto-tune' the SSTC. I'm trying to build a similar system. I
>believe due to noise and (or other reasons?), the PLL would go
>out-of-tune and this may (or may not?) result in HARD switching of
>IGBTs/MOSFETs in the switching circuits or sometimes may result in
>huge currents drawn from the switching circuit. So, is there a way
>to find out if the PLL is 'in tune' or not? Has anyone used the
>'Phase Comparator Pulse Output' (Pin #1) in CD4046BC? Please help.
>
>Thanks and regards,
>Rajesh.
>