Hi Terry,
What Fiber Optic hardware are you using currently? Is it possible to
have the digikey part code for the transmitter and receiver and the
connecting cable?
I have noticed the part lists has one tx device but you seem to be using
a different tx device in the photos,
Adam
-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: 18 January 2005 02:51
To: tesla@xxxxxxxxxx
Subject: Terry's DRSSTC - thoughts...
Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
Hi All,
I played with the "freewheeling" thing (theoretical/models) where one
closes the two lower rail IGBTs to help keep the primary current in the
coil system during turn off. Although it seems to be a good idea, it
just
does not seem to contribute much to the streamer power.... I do wonder
if
having the primary circuit shorted "restricts the freedom" of the
secondary
system to ring freely... It was easy to modify the gate drivers to do
that. You just run the lower ones from "-rail to +rail" so they are
powered for like years on end ;-)) Probably a "good idea" anyway... No
reason to power them from the 100kHz +-170V mess... The top IGBT drives
have to follow the top IGBT emitters, so they are "going for a ride"
anyway...
Freewheeling would pretty much need a PLD to implement which is out of
"my
area"... The TIBPAL16L8-15CN seems like a real nice chip to do it until
one tries to figure out how to program it "these days"! I am not sure
I
trust those new fancy "retains programming for 20 years" microscopic die
things... Whaaa, like in 20 years it forgets a gate, and the thing
blows a
hole through the roof!!! I still use TC stuff I made 30 years ago!
Rather
have like 10,000 years of data retention ;-))) Those <15nS delay times
sure are nice!! ;-))
But some type of "permanent" PLD does seem nice for this DRSSTC control
stuff. I am using 5 ICs now and I might make a four layer board when I
am
"feeling lucky". It needs to be four layer and the cost/"try" is about
$150... So screw ups in the board layout are pretty painful!! But a
nice
CMOS style PLD might make it all real simple. It really is just a
decoder
type of thing... Hard to say what is best since once you have the
"board",
the cost of the little ICs is cheaper than the PLD... But if this ever
goes to a "single board solution", the PLD will avoid the four layer
board
stuff!! Also must beware of the reports that 5V logic and DRSSTCs don't
get along well... My way of thinking is that if noise is getting into
the
logic, the problem is getting rid of the noise rather than changing the
logic... But I respect Dan and Steve's thoughts here and they are
pretty
capable too!! But I think I am keeping the RF stuff pretty well
contained
in the "little" bridge loop too...
So I will continue to explore the freewheeling and PLD things on the
"side". For now they are not needed but it might be cool for the
future. I know three digital gurus so I will ping them for info and
clues... But for now, this seems to be the circuit I am going with:
http://drsstc.com/~terrell/schematics/Controller.gif
I threw all kinds of weird stuff into a model of it today and it always
performed gracefully... I think R7 and R8 might need to be trimmer pots
to
adjust the dead time directly (C10, C11 in the 330pF range)... The
timing
on U5 might have to be shorter on higher Fo coils... Might b4e better
digital solutions there...
I see DigiKey went on backorder for my favorite IRG4PF50WD IGBTs :-(
So
I got 32 of them off supplier "#2" >:o))) NOT(!!) that I am planning
on
blowing any up, but if I do, I don't want to wait until March...
The delay in my digital CT seems to be due to the diodes in the digital
phase detecting CT:
http://drsstc.com/~terrell/schematics/CurrentMeasurement.gif
I use the gate capacitance of the big 1N5337 to sustain the rail
voltage. Might be able to go to smaller diodes but if one fails it
would
be "BAD"! Lots of peak current runs through them... The ones I use now
won't let me down ;-)) The delay only gets better with higher currents
so
I think I will just stay with it and be happy ;-)) I am a little
concerned
about the cheap CTs being able to handle say 500+ amps. I can't test
that
well right now since my high current test machine is in dis-repair... I
will probably have to fix it though to be sure...
So "thinking", while waiting for parts....
Cheers,
Terry