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Re: Terry's DRSSTC -"different" H-drive functions...
Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Steve,
At 02:17 PM 1/13/2005, you wrote:
Hey Terry,
> I am all for recycling. However, I have gone to a lot of trouble getting
> energy into the coil and I really don't want it back ;-)) It looks like
> 154 watts of power is being returned to the buss caps ( @200BPS ). I think
> shorting the two lower FETs is a good idea to keep the power in the
> coil. Pretty simple logic should do it...
I could almost swear that i did a simulation of this (opening all
IGBTs vs closing 2 of them) and could not find a real difference in my
simulations. I assume your simulations are showing a difference?
I just looked at this area:
http://hot-streamer.com/temp/DRSSTC-H-Bridge_Vdiff.gif
http://hot-streamer.com/temp/DRSSTC-H-Bridge_sch.gif
Just found the power going back into the buss and multiplied by the BPS. I
"might" have messed up...
> BTW - ALL my electronics can run from just +5 volts now!! I will have to
> get a 24VDC fan just to say I used the +-12 volts from the fancy power
> supply for something ;O)))
Im not sure that running it all on 5V (or any of it on 5V) is so
great. Yes, i do manage to run my smaller DRSSTCs with 5v logic and
not in a metal box or anything, but on the BIG DRSSTC i had to upgrade
to 15V logic to keep my protection circuits from just going nuts from
the noise. I am much more happy using 15v stuff so long as the
additional delay times are not significant.
All the +-12 volt stuff just sort of went away with design
improvements.... I am sure to use that Schottky +-20mA stuff and keep the
impedance of everything super low. I just made my controller box tonight:
http://drsstc.com/~terrell/pictures/ControllerBox.jpg
Real "versatile" ;-)) I could stuff more boards on the lid side too
;-)) I did look into the freewheeling thing but the simple logic is messy:
http://drsstc.com/~terrell/notes/DRSSTC-Truth.pdf
I think it needs like an EPROM if they even make "simple" ones
anymore... Microcontrollers are too slow so I am thinking of a PROM used
as a state machine... Not my area there so I would have to find someone
with a programmer that knows what buttons to push. I have not done boolean
logic in 25 years so that made my brain hurt %:-)) I don't know anything
about programmable logic, but that seems like what it needs...
>
> Apparently, conducting the tail current in the diodes or on IGBTs presents
> less than a watt of heating... Not an issue...
Its funny how Jimmy, Conner, Myself (and any other DRSSTC guys)
already talked about these things ;-).
Real basic DRSSTC issues that newcomers will be talking about 50 years from
now too ;-))) Glade you guys figure it out already!!
>
> >The Antonio/Hynes style tunings can arrange it so there is practically no
> >energy in the primary when the gate drive ends, which avoids the problem
> >altogether. But probably at the cost of needing a bigger resonator for a
> >given spark length.
I would say its more at the expense of less spark length overall.
Jimmy didn't get *really* good results until he tuned his driver to
the lower frequency of the split. Now he recycles lots of energy too,
but that doesn't seem to matter, last i heard he burnt up his MMCs and
managed something like 96" sparks from his 30" secondary. I suppose
that all the recycled energy does stress out the MMC a bit more than
is needed.
Anyway, my thoughts on this whole thing... It seems that at low power
that indeed quite a bit of energy goes back into the filters at the
end of a burst, but when you start to really get some big streamers,
it seems that is not such an issue anymore. I believe that the
secondary (when using HIGH coupling) is pretty much sucking out energy
so fast that when the burst is over, the left over energy is small. I
need to double check with my scope looking at the primary current (and
bridge output voltage) to double check, but let me tell you, the RF
envelope output definitely changes. You can see that the waveform
gets clamped by the streamer loading it down (streamers seem to be
produced after about 2 cycles when the coil is really blasting them
out ;-)). But, there is almost NO ringdown after the burst, unlike at
low power where there often is a dramatic ringdown afterwards.
Interesting. Like my auto quench coil that just does not get to the second
notch... I don't think my little toy will get as big of streamers as
your's though ;-))
Got the back ordered box for the pulse controller today too but to late to
mill it out. All the H-bridge boards and stuff are due tomorrow so I
should get the H-bridge done then!! Probably two to three weeks away now...
Cheers,
Terry
Hope that makes some sense.
Steve