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Re: Recent s.s.t.c work
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- Subject: Re: Recent s.s.t.c work
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- Date: Mon, 17 Oct 2005 20:07:58 -0600
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Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>
Update #2: Adding 20 uF to the 3 uF drive-xfmr coupling capacitor
did bupkus for the phase shift between the H-bridge supply current
and the primary current. So I looked further and took the photo at
http://www.hot-streamer.com/temp/KCH_TCH7.jpg
It appears that the "phase shift" that has been puzzling me is
nothing more than the to-be-expected turn-on delay in the
IGBTs. Surprise, surprise!
That seems quite clear from the photo: Turn-on of a pair of the
IGBTs occurs about 1 us after the beginning of the + gate
excursion. And turn-off of that pair's reverse-diodes begins about 2
us after the turn-on. Do I have that right?
So...how is one to compensate for that? Does one need to? Can't do
it (that's what I think)? Anyone...?
KCH
And by the way, I realize why the waveforms in my photos appear to
overlap the scope bezel: What appears to be the bezel is actually a
frame in the phosphor of the CRT, not the exterior bezel of the scope.