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Terry's DRSSTC - Bench Test

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi All,

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


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



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:


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!!


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:


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.