Terry's DRSSTC - Bench Test

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Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi All,

Tonight I ran everything on the bench just off four 9V batteries to check 
operation:

http://drsstc.com/~terrell/pictures/BenchTest-01.JPG

It all worked pretty much just as expected.  Here is the output at 40kHz 
and 300kHz:

http://drsstc.com/~terrell/pictures/BenchTest-02-40kHz.gif

http://drsstc.com/~terrell/pictures/BenchTest-03-300kHz.gif

I have the dead times set really high and the load is only a 1k ohm 
resistor so things look a little odd, but this does verify remote control 
to bridge output operation. Yea!!

Interesting to look at the IGBT turn on and off times:

http://drsstc.com/~terrell/pictures/BenchTest-04-Times.gif

The turn on is super fast!  You can see the blip at about 10V where the 
doping regions are tearing themselves on!  The load is trivial here, but 
that will have to be slowed down or the IGBTs will tear themselves apart 
under a real load.  Just a trivial bigger gate resistor...  Turn on is 
rather dull since with such a low load you are just seeing the output 
capacitance and the output MOV discharge curve.  A little cross conduction 
would fix that >:o)

Look at the gates!!

http://drsstc.com/~terrell/pictures/BenchTest-04-Gates.gif

The "pumped" TLP250's and the opto-isolated floating gate drivers have no 
problem at all pushing the gates!  Infact, they drive "too" fast...  Again, 
more gate drive resistance will slow that to a tame speed.  Not sure what 
the bonus down spike is on the turn off...  Might be due to the drive power 
supplies floating or inductance.  It only helps here ;-)  Since I am just 
running off batteries, the gate drive signals here are far less than the 
actual 27V drives:

http://drsstc.com/~terrell/pictures/IGBT-DriveCards-01.gif

So I need to tighten the dead time and play with gate drive resistance.  A 
few more measurements and then I will start bolting it all into the box!


Interesting that Antonio found that the freewheeling thing did not seem to 
help much.  The added electronics to do that is pretty complex and I will 
not miss it ;-))

Steve Ward's data and experiments were really exciting!!!  With 27V of gate 
drive I can run pretty high currents at high speed ;-))  I was planning on 
running very low currents and slow (the exact opposite), but it can run 
just about anything...

Steve Conner's PLL circuit is really cool too!  I think one would have to 
preset the free running frequency pretty close to Fo so it could sync and 
lock in "really fast" (only have 10 cycles according to Steve Ward).  I 
think the start up would also have to be synced with the free running 
oscillator too so the very first turn-ons start together so the PLL error 
signals get off to a good start.

I am still looking into getting those MMC cap PC boards.  Not too many 
people want them so it is sort of on the edge.  I think I can drop the 
order to 16 and still get them for like $37 which might be just right.

Cheers,

	Terry