Re: Recent s.s.t.c. work

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>

Changing the connections of D8 & D9 and upping R6 to ~5 ohms appears 
to have eliminated the apparent oscillation problem; with no h.v. 
applied, everything now remains cool.  But...when I turn up the 
IGBTs' h.v. to perhaps 15% of max., I still find too much dissipation 
in Q2, D8 & R6.  This totally baffles me since the duty cycle is only 
~1.1%, the h.v. only ~15% of full mains, and simulation indicates an 
rms current in R6 of only about 1.7A--but that at (simulated) >full< 
h.v. and 100% d.c.  So the operational rms should be miniscule  The 
scope (connected differentially because of the mains v. present) 
shows a clean gate waveform while those components are getting 
hot.  So something is badly amiss: the circuits should coast along 
under those conditions.

Still at it, altho slowly...

KCH

Tesla list wrote:
> Original poster: "K. C. Herrick" <mailto:kchdlh@xxxxxxx><kchdlh@xxxxxxx>
>
> ...and further:  I find, in the simulation (and on further 
> consideration in the real world), that D8/D9 ought to be connected 
> right at the IGBT gate rather than separated from it by R6.  Moving 
> them in the simulation and upping R6 to 5 ohms or so cuts the 
> oscillation in D8/Q2--but there's some still present in 
> D9/Q3.  Raising R6's resistance to 15 ohms or so also greatly 
> improves the phase-shift problem--but I'd like a better way to do 
> that since such a large R6 starts to roll off the rise/fall of the gate drive.
>
> Maybe more later...
>
> KCH
>
> Tesla list wrote:
> > Original poster: "K. C. Herrick" <mailto:kchdlh@xxxxxxx><kchdlh@xxxxxxx>
> >
> > Here's a bit of a puzzle; perhaps someone can offer a clue toward 
> > solving it.  I post
> >
> > <http://www.hot-streamer.com/temp/tch-drvr.jpg>http://
> [snipped]