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RE: Terry's DRSSTC - All Ready!!
Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Steve,
At 03:32 AM 3/3/2005, you wrote:
>Great. You still have zero margin (spec wise)
I have been bitten before by this "LM339 does crazy things when inputs
pulled below ground" bug. You can see how I worked round it in the OLTC II:
http://www.scopeboy.com/tesla/oltcdriver_1_print.gif
R13 and R21 haul the input up a little so when D3 clamps, the LM339 input is
still within spec. The circuit is a single supply zero crossing detector
straight out of the LM339 application notes, so it wasn't really _me_ who
worked around it :-/
Since the ground line takes a lot of noise, I am a little scarred to float
it up. Right now it works fine, so I figure it works "just fine" ;-))
.................
I also took on board (literally- I'm laying out a PCB) what Terry said about
putting the burden resistor back on the driver board and transferring the CT
signal as a current. I think I'll include that as an option on the board.
Here is how my newest one looks:
http://drsstc.com/~terrell/pcbart/ProtectionCard-02.gif
http://drsstc.com/~terrell/schematics/Protection-1.1.gif
I do all the heavy current stuff for the CT in the lower right...
Here is the other sheet of my driver fwiw. I have since added a UVLO and
some safety interlock and EMI filtering stuff, which is not shown here. By
messing with the many controls on the PLL it can operate on either pole at
will with true zero crossing switching. The first two cycles always look a
bit hairy, it seems to take that long to lock in, but from then on
everything seems OK.
http://www.scopeboy.com/tesla/drsstc/dr3_1.gif
Cool!! Now that I seem to be getting really good analog current info, I
should be looking at better timing the zero current crossing.... I note
that our controller circuits or evolving into pretty sophisticated things
these days!!
If anyone has any comments apart from "Does it work" (cause I'm not sure
myself yet- I have tested it with a mock-up of two coupled resonators but
not a real Tesla coil) please go ahead.
Steve C.
Working on new MMC tonight:
http://drsstc.com/~terrell/pictures/NewMMC.JPG
Waiting for the glues to dry....
http://drsstc.com/~terrell/pictures/Mar3Lab.JPG
Cheers,
Terry